x86-64 is an extension of the x86 instruction set. It supports vastly larger virtual and physical address spaces than are possible on x86, thereby allowing programmers to conveniently work with much larger data sets. x86-64 also provides
64-bit64-bit is a word size that defines certain classes of computer architecture, buses, memory and CPUs, and by extension the software that runs on them. 64-bit CPUs have existed in supercomputers since the 1970s and in RISC-based workstations and servers since the early 1990s...
general purpose registers and numerous other enhancements. The original specification was created by
AMDAdvanced Micro Devices, Inc. or AMD is an American multinational semiconductor company based in Sunnyvale, California, that develops computer processors and related technologies for commercial and consumer markets...
, and has been implemented by AMD,
IntelIntel Corporation is an American multinational semiconductor chip maker corporation headquartered in Santa Clara, California, United States and the world's largest semiconductor chip maker, based on revenue. It is the inventor of the x86 series of microprocessors, the processors found in most...
,
VIAVIA Technologies is a Taiwanese manufacturer of integrated circuits, mainly motherboard chipsets, CPUs, and memory, and is part of the Formosa Plastics Group. It is the world's largest independent manufacturer of motherboard chipsets...
, and others. It is fully backwards compatible with
32-bitThe range of integer values that can be stored in 32 bits is 0 through 4,294,967,295. Hence, a processor with 32-bit memory addresses can directly access 4 GB of byte-addressable memory....
code. Because the full 32-bit instruction set remains implemented in hardware without any intervening emulation, existing 32-bit x86
executableIn computing, an executable file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a data file that must be parsed by a program to be meaningful. These instructions are traditionally machine code instructions for a physical CPU...
s run with no compatibility or performance penalties,
although existing applications that are recoded to take advantage of new features of the processor design may see significant performance increases.
After launching the architecture under the "x86-64" name, AMD renamed it
AMD64 in 2003; Intel initially used the names
IA-32e and
EM64T before finally settling on
Intel 64 for their implementation. x86-64 is still used by many in the industry as a vendor-neutral term, while others, notably
Sun MicrosystemsSun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
(now
Oracle CorporationOracle Corporation is an American multinational computer technology corporation that specializes in developing and marketing hardware systems and enterprise software products – particularly database management systems...
) and
MicrosoftMicrosoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
, use
x64.
The
AMD K8The AMD K8 is a computer processor microarchitecture designed by AMD as the successor to the AMD K7 microarchitecture. The K8 was the first implementation of the AMD64 64-bit extension to the x86 processor architecture.Processors based on the K8 core include:...
core was the first to implement the architecture; this was the first significant addition to the x86 architecture designed by a company other than Intel. Intel was forced to follow suit and introduced a modified NetBurst family which was fully software-compatible with AMD's design and specification.
VIA TechnologiesVIA Technologies is a Taiwanese manufacturer of integrated circuits, mainly motherboard chipsets, CPUs, and memory, and is part of the Formosa Plastics Group. It is the world's largest independent manufacturer of motherboard chipsets...
introduced x86-64 in their VIA Isaiah architecture, with the
VIA NanoThe VIA Nano is a 64-bit CPU for personal computers. The VIA Nano was released by VIA Technologies in 2008 after five years of development by its CPU division, Centaur Technology...
.
The x86-64 specification is distinct from the Intel
ItaniumItanium is a family of 64-bit Intel microprocessors that implement the Intel Itanium architecture . Intel markets the processors for enterprise servers and high-performance computing systems...
(formerly
IA-64) architecture, which is not compatible on the native instruction set level with the x86 architecture.
AMD64
The AMD64 instruction set is implemented in AMD's
Athlon 64The Athlon 64 is an eighth-generation, AMD64-architecture microprocessor produced by AMD, released on September 23, 2003. It is the third processor to bear the name Athlon, and the immediate successor to the Athlon XP...
,
Athlon 64 FXThe Athlon 64 is an eighth-generation, AMD64-architecture microprocessor produced by AMD, released on September 23, 2003. It is the third processor to bear the name Athlon, and the immediate successor to the Athlon XP...
,
Athlon 64 X2The Athlon 64 X2 is the first dual-core desktop CPU designed by AMD. It was designed from scratch as native dual-core by using an already multi-CPU enabled Athlon 64, joining it with another functional core on one die, and connecting both via a shared dual-channel memory controller/north bridge and...
,
Athlon IIAthlon II is a family of AMD multi-core 45 nm central processing units, which is aimed at the midrange to budget market and is a complementary product lineup to the Phenom II.-Features:...
, Athlon X2,
OpteronOpteron is AMD's x86 server and workstation processor line, and was the first processor which supported the AMD64 instruction set architecture . It was released on April 22, 2003 with the SledgeHammer core and was intended to compete in the server and workstation markets, particularly in the same...
,
PhenomPhenom is the 64-bit AMD desktop processor line based on the K10 microarchitecture, in what AMD calls family 10h processors, sometimes incorrectly called "K10h". Triple-core versions belong to the Phenom 8000 series and quad cores to the AMD Phenom X4 9000 series...
,
Phenom IIPhenom II is a family of AMD's multi-core 45 nm processors using the AMD K10 microarchitecture, succeeding the original Phenom. Advanced Micro Devices released the Socket AM2+ version of Phenom II in December 2008, while Socket AM3 versions with DDR3 support, along with an initial batch of...
, Turion 64, Turion 64 X2, and later
SempronSempron has been the marketing name used by AMD for several different budget desktop CPUs, using several different technologies and CPU socket formats. The Sempron replaced the AMD Duron processor and competes against Intel's Celeron series of processors...
processors.
History of AMD64
AMD64 was created as an alternative to the radically different IA-64 architecture, which was designed by Intel and Hewlett Packard. Originally announced in 1999 with a full specification in August 2000, the architecture was positioned by AMD from the beginning as an evolutionary way to add 64-bit computing capabilities to the existing x86 architecture, as opposed to Intel's approach of creating an entirely new 64-bit architecture with IA-64.
The first AMD64-based processor, the
OpteronOpteron is AMD's x86 server and workstation processor line, and was the first processor which supported the AMD64 instruction set architecture . It was released on April 22, 2003 with the SledgeHammer core and was intended to compete in the server and workstation markets, particularly in the same...
, was released in April 2003.
Architectural features
The primary defining characteristic of AMD64 is the availability of 64-bit general-purpose
processor registerIn computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are addressed by mechanisms other than main memory and can be accessed more quickly...
s, e.g. rax, rbx etc., 64-bit
integerIn computer science, an integer is a datum of integral data type, a data type which represents some finite subset of the mathematical integers. Integral data types may be of different sizes and may or may not be allowed to contain negative values....
arithmetic and logical operations, and 64-bit virtual addresses. The designers took the opportunity to make other improvements as well. The most significant changes include:
- 64-bit integer capability: All general-purpose registers (GPRs) are expanded from 32 bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
s to 64 bits, and all arithmetic and logical operations, memory-to-register and register-to-memory operations, etc., can now operate directly on 64-bit integers. Pushes and popsIn computer science, a stack is a last in, first out abstract data type and linear data structure. A stack can have any abstract data type as an element, but is characterized by only three fundamental operations: push, pop and stack top. The push operation adds a new item to the top of the stack,...
on the stackA stack register is a computer central processor register whose purpose is to keep track of a call stack. On an accumulator-based architecture machine, this may be a dedicated register such as SP on an Intel x86 machine. On a general register machine, it may be a register which is reserved by...
are always in 8-byte strides, and pointers are 8 bytes wide.
- Additional registers: In addition to increasing the size of the general-purpose registers, the number of named general-purpose registers is increased from eight (i.e. eax, ebx, ecx, edx, ebp, esp, esi, edi) in x86 to 16 (i.e. rax, rbx, rcx, rdx, rbp, rsp, rsi, rdi, r8, r9, r10, r11, r12, r13, r14, r15). It is therefore possible to keep more local variables in registers rather than on the stack, and to let registers hold frequently accessed constants; arguments for small and fast subroutines may also be passed in registers to a greater extent. However, AMD64 still has fewer registers than many common RISC ISAs (which typically have 32–64 registers) or VLIW-like machines such as the IA-64 (which has 128 registers); note, however, that because of register renaming
In computer architecture, register renaming refers to a technique used to avoid unnecessary serialization of program operations imposed by the reuse of registers by those operations.-Problem definition:...
the number of physical registers is often much larger than the number of registers exposed by the instruction set.
- Additional XMM (SSE) registers: Similarly, the number of 128-bit XMM registers (used for Streaming SIMD
In computing, Streaming SIMD Extensions is a SIMD instruction set extension to the x86 architecture, designed by Intel and introduced in 1999 in their Pentium III series processors as a reply to AMD's 3DNow! . SSE contains 70 new instructions, most of which work on single precision floating point...
instructions) is also increased from 8 to 16.
- Larger virtual address space: The AMD64 architecture defines a 64-bit virtual address format, of which the low-order 48 bits are used in current implementations. This allows up to 256 TB
The terabyte is a multiple of the unit byte for digital information. The prefix tera means 1012 in the International System of Units , and therefore 1 terabyte is , or 1 trillion bytes, or 1000 gigabytes. 1 terabyte in binary prefixes is 0.9095 tebibytes, or 931.32 gibibytes...
(248 byteThe byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
s) of virtual address space. The architecture definition allows this limit to be raised in future implementations to the full 64 bits, extending the virtual address space to 16 EBThe exabyte is a unit of information or computer storage equal to one quintillion bytes . The unit symbol for the exabyte is EB...
(264 bytes). This is compared to just 4 GBThe gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
(232 bytes) for the x86. This means that very large files can be operated on by mappingA memory-mapped file is a segment of virtual memory which has been assigned a direct byte-for-byte correlation with some portion of a file or file-like resource. This resource is typically a file that is physically present on-disk, but can also be a device, shared memory object, or other resource...
the entire file into the process' address space (which is often much faster than working with file read/write calls), rather than having to map regions of the file into and out of the address space.
- Larger physical address space: The original implementation of the AMD64 architecture implemented 40-bit physical addresses and so could address up to 1 TB (240 bytes) of RAM. Current implementations of the AMD64 architecture (starting from AMD 10h microarchitecture
The AMD Family 10h is a microprocessor microarchitecture by AMD. Though there were once reports that the K10 had been canceled, the first third-generation Opteron products for servers were launched on September 10, 2007, with the Phenom processors for desktops following and launching on November...
) extend this to 48-bit physical addresses and therefore can address up to 256 TB of RAM. The architecture permits extending this to 52 bits in the future (limited by the page table entry format); this would allow addressing of up to 4 PBA petabyte is a unit of information equal to one quadrillion bytes, or 1000 terabytes. The unit symbol for the petabyte is PB...
of RAM. For comparison, 32-bit x86 processors are limited to 64 GB of RAM in Physical Address ExtensionIn computing, Physical Address Extension is a feature to allow x86 processors to access a physical address space larger than 4 gigabytes....
(PAE) mode, or 4 GB of RAM without PAE mode.
- Larger physical address space in legacy mode: When operating in legacy mode
In computing, legacy mode is a state in which a computer system, component, or software application behaves in a way different from its standard operation in order to support older software, data, or expected behavior...
the AMD64 architecture supports Physical Address ExtensionIn computing, Physical Address Extension is a feature to allow x86 processors to access a physical address space larger than 4 gigabytes....
(PAE) mode, as do most current x86 processors, but AMD64 extends PAE from 36 bits to an architectural limit of 52 bits of physical address. Any implementation therefore allows the same physical address limit as under long mode.
- Instruction pointer relative data access: Instructions can now reference data relative to the instruction pointer (RIP register). This makes position independent code, as is often used in shared libraries and code loaded at run time, more efficient.
- SSE instructions: The original AMD64 architecture adopted Intel's SSE
In computing, Streaming SIMD Extensions is a SIMD instruction set extension to the x86 architecture, designed by Intel and introduced in 1999 in their Pentium III series processors as a reply to AMD's 3DNow! . SSE contains 70 new instructions, most of which work on single precision floating point...
and SSE2SSE2, Streaming SIMD Extensions 2, is one of the Intel SIMD processor supplementary instruction sets first introduced by Intel with the initial version of the Pentium 4 in 2001. It extends the earlier SSE instruction set, and is intended to fully supplant MMX. Intel extended SSE2 to create SSE3...
as core instructions. SSE3SSE3, Streaming SIMD Extensions 3, also known by its Intel code name Prescott New Instructions , is the third iteration of the SSE instruction set for the IA-32 architecture. Intel introduced SSE3 in early 2004 with the Prescott revision of their Pentium 4 CPU...
instructions were added in April 2005. SSE2 is an alternative to the x87x87 is a floating point-related subset of the x86 architecture instruction set. It originated as an extension of the 8086 instruction set in the form of optional floating point coprocessors that worked in tandem with corresponding x86 CPUs. These microchips had names ending in "87"...
instruction set's IEEE 80-bit precisionIEEE 754–1985 was an industry standard for representingfloating-pointnumbers in computers, officially adopted in 1985 and superseded in 2008 byIEEE 754-2008. During its 23 years, it was the most widely used format for...
with the choice of either IEEE 32-bit or 64-bit floating-point mathematics. This provides floating-point operations compatible with many other modern CPUs. The SSE and SSE2 instructions have also been extended to operate on the eight new XMM registers. SSE and SSE2 are available in 32-bit mode in modern x86 processors; however, if they're used in 32-bit programs, those programs will only work on systems with processors that have the feature. This is not an issue in 64-bit programs, as all AMD64 processors have SSE and SSE2, so using SSE and SSE2 instructions instead of x87 instructions does not reduce the set of machines on which x86-64 programs can be run. SSE and SSE2 are generally faster than, and duplicate most of the features of the traditional x87 instructions, MMX, and 3DNow!3DNow! is an extension to the x86 instruction set developed by Advanced Micro Devices . It adds single instruction multiple data instructions to the base x86 instruction set, enabling it to perform simple vector processing, which improves the performance of many graphic-intensive applications...
.
- No-Execute bit
The NX bit, which stands for No eXecute, is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions or for storage of data, a feature normally only found in Harvard architecture processors...
: The "NX" bit (bit 63 of the page table entry) allows the operating system to specify which pages of virtual address space can contain executable code and which cannot. An attempt to execute code from a page tagged "no execute" will result in a memory access violation, similar to an attempt to write to a read-only page. This should make it more difficult for malicious code to take control of the system via "buffer overrunIn computer security and programming, a buffer overflow, or buffer overrun, is an anomaly where a program, while writing data to a buffer, overruns the buffer's boundary and overwrites adjacent memory. This is a special case of violation of memory safety....
" or "unchecked buffer" attacks. A similar feature has been available on x86 processors since the 80286 as an attribute of segment descriptors; however, this works only on an entire segment at a time. Segmented addressing has long been considered an obsolete mode of operation, and all current PC operating systems in effect bypass it, setting all segments to a base address of 0 and (in their 32 bit implementation) a size of 4 GB. AMD was the first x86-family vendor to implement no-execute in linear addressing mode. The feature is also available in legacy mode on AMD64 processors, and recent Intel x86 processors, when PAE is used.
- Removal of older features: A number of "system programming" features of the x86 architecture are not used in modern operating systems and are not available on AMD64 in long (64-bit and compatibility) mode. These include segmented addressing (although the FS and GS segments are retained in vestigial form for use as extra base pointers to operating system structures), the task state switch
The task state segment is a special structure on x86-based computers which holds information about a task. It is used by the operating system kernel for task management...
mechanism, and Virtual 8086 modeIn the 80386 microprocessor and later, virtual 8086 mode allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running a protected mode operating system.VM86 mode uses a segmentation scheme identical to that of real mode In...
. These features remain fully implemented in "legacy mode," thus permitting these processors to run 32-bit and 16-bit operating systems without modification.
Canonical form addresses
Although virtual addresses are 64 bits wide in 64-bit mode, current implementations (and all chips known to be in the planning stages) do not allow the entire virtual address space of 2
64 bytes (16 EB) to be used. Most operating systems and applications will not need such a large address space for the foreseeable future (for example, Windows implementations for AMD64 are only populating 16 TB, or 44 bits' worth), so implementing such wide virtual addresses would simply increase the complexity and cost of address translation with no real benefit. AMD therefore decided that, in the first implementations of the architecture, only the least significant 48 bits of a virtual address would actually be used in address translation (
page tableA page table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual addresses and physical addresses. Virtual addresses are those unique to the accessing process...
lookup). Further, bits 48 through 63 of any virtual address must be copies of bit 47 (in a manner akin to
sign extensionSign extension is the operation, in computer arithmetic, of increasing the number of bits of a binary number while preserving the number's sign and value...
), or the processor will raise an exception. Addresses complying with this rule are referred to as "canonical form." Canonical form addresses run from 0 through 00007FFF'FFFFFFFF, and from FFFF8000'00000000 through FFFFFFFF'FFFFFFFF, for a total of 256 TB of usable virtual address space.
This "quirk" allows an important feature for later scalability to true 64-bit addressing:
many operating systems (including, but not limited to, the
Windows NTWindows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
family) take the higher-addressed half of the address space (named kernel space) for themselves and leave the lower-addressed half (user space) for application code, user mode stacks, heaps, and other data regions. The "canonical address" design ensures that every AMD64 compliant implementation has, in effect, two memory halves: the lower half starts at 00000000'00000000 and "grows upwards" as more virtual address bits become available, while the higher half is "docked" to the top of the address space and grows downwards. Also, fixing the contents of the unused address bits prevents their use by operating system as flags, privilege markers, etc., as such use could become problematic when the architecture is extended to implement more bits of virtual addresses.
Current 48-bit implementation
 |
56-bit implementation
 |
Full 64-bit implementation
 |
|
Page table structure
The 64-bit addressing mode ("
long modeIn the x86-64 computer architecture, long mode is the mode where a 64-bit application can access 64-bit instructions and registers...
") is a superset of
Physical Address ExtensionIn computing, Physical Address Extension is a feature to allow x86 processors to access a physical address space larger than 4 gigabytes....
s (PAE); because of this,
pageIn computer operating systems, paging is one of the memory-management schemes by which a computer can store and retrieve data from secondary storage for use in main memory. In the paging memory-management scheme, the operating system retrieves data from secondary storage in same-size blocks called...
sizes may be 4
KBThe kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
(2
12 bytes) or 2
MBThe megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
(2
21 bytes). Long mode also supports page sizes of 1
GBThe gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
(2
30 bytes). Rather than the three-level
page tableA page table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual addresses and physical addresses. Virtual addresses are those unique to the accessing process...
system used by systems in PAE mode, systems running in
long modeIn the x86-64 computer architecture, long mode is the mode where a 64-bit application can access 64-bit instructions and registers...
use four levels of page table: PAE's
Page-Directory Pointer Table is extended from 4 entries to 512, and an additional
Page-Map Level 4 (PML4) Table is added, containing 512 entries in 48-bit implementations. In implementations providing larger virtual addresses, this latter table would either grow to accommodate sufficient entries to describe the entire address range, up to a theoretical maximum of 33,554,432 entries for a 64-bit implementation, or be over ranked by a new mapping level, such as a PML5. A full mapping hierarchy of 4 KB pages for the whole 48-bit space would take a bit more than 512 GB of RAM (about 0.196% of the 256 TB virtual space).
Operating system limits
The operating system can also limit the virtual address space. Details, where applicable, are given in the "Operating system compatibility and characteristics" section.
Physical address space details
Current AMD64 implementations support a physical address space of up to 2
48 bytes of RAM, or 256 TB,. A larger amount of installed RAM allows the operating system to keep more of the workload's pageable data and code in RAM, which can improve performance, though various workloads will have different points of diminishing returns.
The upper limit on RAM that can be used in a given x86-64 system depends on a variety of factors and can be far less than that implemented by the processor. For example, as of June 2010, there are no known
motherboardIn personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...
s for x86-64 processors that support 256 TB of RAM. The operating system may place additional limits on the amount of RAM that is usable or supported. Details on this point are given in the "Operating system compatibility and characteristics" section of this article.
Operating modes
| Operating mode |
Operating system An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
required |
Compiled-application rebuild required |
Default address size |
Default operand size |
Register extensions |
Typical GPR width |
| Long mode In the x86-64 computer architecture, long mode is the mode where a 64-bit application can access 64-bit instructions and registers...
|
64-bit mode |
OS with 64-bit support, or bootloader for 64-bit OS |
Yes |
64 |
32 |
Yes |
64 |
| Compatibility mode |
No |
32 |
32 |
No |
32 |
| 16 |
16 |
16 |
| Legacy mode |
Protected mode In computing, protected mode, also called protected virtual address mode, is an operational mode of x86-compatible central processing units...
|
Legacy 16-bit or 32-bit OS; or bootloader for 16, 32, or 64-bit OS |
No |
32 |
32 |
No |
32 |
| 16 |
16 |
16 |
| Virtual 8086 mode In the 80386 microprocessor and later, virtual 8086 mode allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running a protected mode operating system.VM86 mode uses a segmentation scheme identical to that of real mode In...
|
Legacy 16-bit or 32-bit OS |
16 |
16 |
16 |
| Real mode Real mode, also called real address mode, is an operating mode of 80286 and later x86-compatible CPUs. Real mode is characterized by a 20 bit segmented memory address space and unlimited direct software access to all memory, I/O addresses and peripheral hardware...
|
Legacy 16-bit OS; or bootloader for 16, 32, or 64 bit OS |
The architecture has two primary modes of operation:
Long mode
The architecture's intended primary mode of operation; it is a combination of the processor's native 64-bit mode and a combined 32-bit and 16-bit compatibility mode. It is used by 64-bit operating systems. Under a 64-bit operating system, 64-bit programs run under 64-bit mode, and 32-bit and 16-bit protected mode applications (that do not need to use either real mode or virtual 8086 mode in order to execute at any time) run under compatibility mode. Real-mode programs and programs that use virtual 8086 mode at any time cannot be run in long mode unless they are emulated in software.
Since the basic instruction set is the same, there is almost no performance penalty for executing protected mode x86 code. This is unlike Intel's IA-64, where differences in the underlying ISA means that running 32-bit code must be done either in emulation of x86 (making the process slower) or with a dedicated x86 core. However, on the x86-64 platform, many x86 applications could benefit from a 64-bit recompile, due to the additional registers in 64-bit code and guaranteed SSE2-based FPU support, which a
compilerA compiler is a computer program that transforms source code written in a programming language into another computer language...
can use for optimization. However, applications that regularly handle integers wider than 32 bits, such as cryptographic algorithms, will need a rewrite of the code handling the huge integers in order to take advantage of the 64-bit registers.
Legacy mode
The mode used by 16-bit (protected mode or real mode) and 32-bit operating systems. In this mode, the processor acts like a 32-bit x86 processor, and only 16-bit or 32-bit code can be executed. Legacy mode allows for a maximum of 32 bit virtual addressing which limits the virtual address space to 4 GB. 64-bit programs cannot be run from legacy mode.
AMD64 implementations
The following processors implement the AMD64 architecture:
- AMD Athlon 64
The Athlon 64 is an eighth-generation, AMD64-architecture microprocessor produced by AMD, released on September 23, 2003. It is the third processor to bear the name Athlon, and the immediate successor to the Athlon XP...
- AMD Athlon 64 X2
The Athlon 64 X2 is the first dual-core desktop CPU designed by AMD. It was designed from scratch as native dual-core by using an already multi-CPU enabled Athlon 64, joining it with another functional core on one die, and connecting both via a shared dual-channel memory controller/north bridge and...
- AMD Athlon 64 FX
The Athlon 64 is an eighth-generation, AMD64-architecture microprocessor produced by AMD, released on September 23, 2003. It is the third processor to bear the name Athlon, and the immediate successor to the Athlon XP...
- AMD Athlon II
Athlon II is a family of AMD multi-core 45 nm central processing units, which is aimed at the midrange to budget market and is a complementary product lineup to the Phenom II.-Features:...
(followed by 'X2', 'X3', or 'X4' to indicate the number of cores, and XLT models)
- AMD Opteron
Opteron is AMD's x86 server and workstation processor line, and was the first processor which supported the AMD64 instruction set architecture . It was released on April 22, 2003 with the SledgeHammer core and was intended to compete in the server and workstation markets, particularly in the same...
- AMD Turion 64
- AMD Turion 64 X2
- AMD Sempron
Sempron has been the marketing name used by AMD for several different budget desktop CPUs, using several different technologies and CPU socket formats. The Sempron replaced the AMD Duron processor and competes against Intel's Celeron series of processors...
("Palermo" E6 stepping and all "Manila" models)
- AMD Phenom
Phenom is the 64-bit AMD desktop processor line based on the K10 microarchitecture, in what AMD calls family 10h processors, sometimes incorrectly called "K10h". Triple-core versions belong to the Phenom 8000 series and quad cores to the AMD Phenom X4 9000 series...
(followed by 'X3' or 'X4' to indicate the number of cores)
- AMD Phenom II
Phenom II is a family of AMD's multi-core 45 nm processors using the AMD K10 microarchitecture, succeeding the original Phenom. Advanced Micro Devices released the Socket AM2+ version of Phenom II in December 2008, while Socket AM3 versions with DDR3 support, along with an initial batch of...
(followed by 'X2', 'X3', 'X4' or 'X6' to indicate the number of cores)
Intel 64
Intel 64 is Intel's implementation of x86-64. It is used in newer versions of
Pentium 4Pentium 4 was a line of single-core desktop and laptop central processing units , introduced by Intel on November 20, 2000 and shipped through August 8, 2008. They had a 7th-generation x86 microarchitecture, called NetBurst, which was the company's first all-new design since the introduction of the...
, Celeron D,
XeonThe Xeon is a brand of multiprocessing- or multi-socket-capable x86 microprocessors from Intel Corporation targeted at the non-consumer server, workstation and embedded system markets.-Overview:...
and Pentium Dual-Core processors, the
AtomIntel Atom is the brand name for a line of ultra-low-voltage x86 and x86-64 CPUs from Intel, designed in 45 nm CMOS and used mainly in netbooks, nettops, embedded application ranging from health care to advanced robotics and Mobile Internet devices...
D510, N450, and N550, and in all versions of the Pentium Extreme Edition, Core 2, Core i7, Core i5, and Core i3 processors.
History of Intel 64
Historically, AMD has developed and produced processors patterned after Intel's original designs, but with x86-64, roles were reversed: Intel found itself in the position of adopting the architecture which AMD had created as an extension to Intel's own x86 processor line.
Intel's project was originally codenamed
Yamhill (after the
Yamhill RiverThe Yamhill River is an tributary of the Willamette River, in the U.S. state of Oregon. Formed by the confluence of the South Yamhill River and the North Yamhill River about east of McMinnville, it drains part of the Northern Oregon Coast Range...
in Oregon's Willamette Valley). After several years of denying its existence, Intel announced at the February 2004
IDFIntel Developer Forum , is a gathering of technologists to discuss Intel products and products based around Intel products. The first IDF was in 1997...
that the project was indeed underway. Intel's chairman at the time,
Craig BarrettCraig R. Barrett is an American business executive who served as the chairman of the board of the Intel Corporation until May 2009. He became CEO of Intel in 1998, a position he held for seven years...
, admitted that this was one of their worst kept secrets.
Intel's name for this instruction set has changed several times. The name used at the IDF was
CT (presumably for
Clackamas Technology, another codename from an
Oregon riverThe Clackamas River is an approximately tributary of the Willamette River in northwestern Oregon, in the United States. As it drains an area of about , the Clackamas passes through mostly forested and rugged mountainous terrain in its upper reaches, and passes through agricultural and urban areas...
); within weeks they began referring to it as
IA-32e (for
IA-32IA-32 , also known as x86-32, i386 or x86, is the CISC instruction-set architecture of Intel's most commercially successful microprocessors, and was first implemented in the Intel 80386 as a 32-bit extension of x86 architecture...
extensions) and in March 2004 unveiled the "official" name
EM64T (Extended Memory 64 Technology). In late 2006 Intel began instead using the name
Intel 64 for its implementation, paralleling AMD's use of the name AMD64.
Intel 64 implementations
The first processor to implement Intel 64 was the multi-socket processor
XeonThe Xeon is a brand of multiprocessing- or multi-socket-capable x86 microprocessors from Intel Corporation targeted at the non-consumer server, workstation and embedded system markets.-Overview:...
code-named
Nocona in June 2004. In contrast, the initial Prescott chips (February 2004) did not enable this feature. Intel subsequently began selling Intel 64-enabled Pentium 4s using the E0 revision of the Prescott core, being sold on the OEM market as the Pentium 4, model F. The E0 revision also adds eXecute Disable (XD) (Intel's name for the
NX bitThe NX bit, which stands for No eXecute, is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions or for storage of data, a feature normally only found in Harvard architecture processors...
) to Intel 64, and has been included in then current Xeon code-named
Irwindale. Intel's official launch of Intel 64 (under the name EM64T at that time) in mainstream desktop processors was the N0 Stepping Prescott-2M. All 9xx, 8xx, 6xx, 5x9, 5x6, 5x1, 3x6, and 3x1 series CPUs have Intel 64 enabled, as do the Core 2 CPUs, as will future Intel CPUs for workstations or servers. Intel 64 is also present in the last members of the Celeron D line.
The first Intel
mobile processorA mobile processor is a CPU designed to save power. It is found in mobile computers and cellphones.A CPU chip designed for portable computers, it is typically housed in a smaller chip package, but more importantly, in order to run cooler, it uses lower voltages than its desktop counterpart and has...
implementing Intel 64 is the
MeromMerom is the code name for various Intel processors that are sold as Core 2 Duo, Core 2 Solo, Pentium Dual-Core and Celeron. It was the first mobile processor to be based on the Core microarchitecture, replacing the Enhanced Pentium M based Yonah processor. Merom has product code 80537, which is...
version of the Core 2 processor, which was released on 27 July 2006. None of Intel's earlier notebook CPUs (Core Duo,
Pentium MThe Pentium M brand refers to a family of mobile single-core x86 microprocessors introduced in March 2003 , and forming a part of the Intel Carmel notebook platform under the then new Centrino brand...
, Celeron M,
Mobile Pentium 4Pentium 4 was a line of single-core desktop and laptop central processing units , introduced by Intel on November 20, 2000 and shipped through August 8, 2008. They had a 7th-generation x86 microarchitecture, called NetBurst, which was the company's first all-new design since the introduction of the...
) implements Intel 64.
The following processors implement the Intel 64 architecture:
- Intel NetBurst microarchitecture
- Intel Xeon
The Xeon is a brand of multiprocessing- or multi-socket-capable x86 microprocessors from Intel Corporation targeted at the non-consumer server, workstation and embedded system markets.-Overview:...
(all models since "Nocona")
- Intel Celeron
Celeron is a brand name given by Intel Corp. to a number of different x86 computer microprocessor models targeted at budget personal computers....
(some models since "Prescott")
- Intel Pentium 4
Pentium 4 was a line of single-core desktop and laptop central processing units , introduced by Intel on November 20, 2000 and shipped through August 8, 2008. They had a 7th-generation x86 microarchitecture, called NetBurst, which was the company's first all-new design since the introduction of the...
(some models since "Prescott")
- Intel Pentium D
The Pentium D brand refers to two series of desktop dual-core 64-bit x86-64 microprocessors with the NetBurst microarchitecture manufactured by Intel. Each CPU comprised two dies, each containing a single core, residing next to each other on a multi-chip module package. The brand's first processor,...
- Intel Pentium Extreme Edition
- Intel Core microarchitecture
- Intel Xeon
The Xeon is a brand of multiprocessing- or multi-socket-capable x86 microprocessors from Intel Corporation targeted at the non-consumer server, workstation and embedded system markets.-Overview:...
(all models since "Woodcrest")
- Intel Core 2
Core 2 is a brand encompassing a range of Intel's consumer 64-bit x86-64 single-, dual-, and quad-core microprocessors based on the Core microarchitecture. The single- and dual-core models are single-die, whereas the quad-core models comprise two dies, each containing two cores, packaged in a...
(including Mobile processors since "Merom")
- Intel Pentium Dual-Core (E2140, E2160, E2180, E2200, E2220, E5200, E5300, E5400, E6300, E6500, T2310, T2330, T2370, T2390, T3200 and T3400)
- Intel Celeron
Celeron is a brand name given by Intel Corp. to a number of different x86 computer microprocessor models targeted at budget personal computers....
(Celeron 4x0; Celeron M 5xx; E3200, E3300, E3400)
- Intel Atom microarchitecture
- Intel Atom
Intel Atom is the brand name for a line of ultra-low-voltage x86 and x86-64 CPUs from Intel, designed in 45 nm CMOS and used mainly in netbooks, nettops, embedded application ranging from health care to advanced robotics and Mobile Internet devices...
200 series (not to be confused with the N200 series, widely used in netbookNetbooks are a category of small, lightweight, legacy-free, and inexpensive laptop computers.At their inception in late 2007 as smaller notebooks optimized for low weight and low cost — netbooks omitted certain features , featured smaller screens and keyboards, and offered reduced computing...
s)
- Intel Atom
Intel Atom is the brand name for a line of ultra-low-voltage x86 and x86-64 CPUs from Intel, designed in 45 nm CMOS and used mainly in netbooks, nettops, embedded application ranging from health care to advanced robotics and Mobile Internet devices...
300 series
- Intel Atom
Intel Atom is the brand name for a line of ultra-low-voltage x86 and x86-64 CPUs from Intel, designed in 45 nm CMOS and used mainly in netbooks, nettops, embedded application ranging from health care to advanced robotics and Mobile Internet devices...
N4xx, N5xx series
- Intel Atom
Intel Atom is the brand name for a line of ultra-low-voltage x86 and x86-64 CPUs from Intel, designed in 45 nm CMOS and used mainly in netbooks, nettops, embedded application ranging from health care to advanced robotics and Mobile Internet devices...
Dxxx series
- Intel Nehalem microarchitecture
- Intel Core i3
- Intel Core i5
- Intel Core i7
- Intel Sandy Bridge microarchitecture
Sandy Bridge is the codename for a microarchitecture developed by Intel beginning in 2005 for central processing units in computers to replace the Nehalem microarchitecture...
- Intel Core i3
- Intel Core i5
- Intel Core i7
VIA's x86-64 implementation
- VIA Technologies
VIA Technologies is a Taiwanese manufacturer of integrated circuits, mainly motherboard chipsets, CPUs, and memory, and is part of the Formosa Plastics Group. It is the world's largest independent manufacturer of motherboard chipsets...
Isaiah microarchitecture, implemented in the VIA NanoThe VIA Nano is a 64-bit CPU for personal computers. The VIA Nano was released by VIA Technologies in 2008 after five years of development by its CPU division, Centaur Technology...
The
VIA Nano (formerly code named
VIA Isaiah) is a
64-bit64-bit is a word size that defines certain classes of computer architecture, buses, memory and CPUs, and by extension the software that runs on them. 64-bit CPUs have existed in supercomputers since the 1970s and in RISC-based workstations and servers since the early 1990s...
CPU for
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s. The
VIA Nano was released by
VIA TechnologiesVIA Technologies is a Taiwanese manufacturer of integrated circuits, mainly motherboard chipsets, CPUs, and memory, and is part of the Formosa Plastics Group. It is the world's largest independent manufacturer of motherboard chipsets...
in 2008 after five years of development by its CPU division,
Centaur TechnologyCentaur Technology is an x86 CPU design company, now a wholly owned subsidiary of VIA Technologies, a member of the Formosa Plastics Group, Taiwan's largest industrial conglomerate.-History:...
. This new Isaiah 64-bit architecture was designed from scratch, unveiled on 24 January 2008, and launched on May 29, including low-voltage variants and the Nano brand name. The processor supports a number of VIA-specific x86 extensions designed to boost efficiency in low-power appliances.
It is expected that the VIA Isaiah will be twice as fast in integer performance and four times as fast in floating-point performance as the previous-generation VIA Esther at an equivalent clock speed. Power consumption is also expected to be on par with the previous-generation VIA CPUs, with
thermal design powerThe thermal design power , sometimes called thermal design point, refers to the maximum amount of power the cooling system in a computer is required to dissipate. For example, a laptop's CPU cooling system may be designed for a 20 watt TDP, which means that it can dissipate up to 20 watts of heat...
ranging from 5 W to 25 W. Being a completely new design, the Isaiah architecture was built with support for features like the x86-64 instruction set and
x86 virtualizationIn computing, x86 virtualization is the facility that allows multiple operating systems to simultaneously share x86 processor resources in a safe and efficient manner, a facility generically known as hardware virtualization...
which were unavailable on its predecessors, the
VIA C7The VIA C7 is an x86 central processing unit designed by Centaur Technology and sold by VIA Technologies.- Product history :The C7 delivers a number of improvements to the older VIA C3 cores but is nearly identical to the latest VIA C3 Nehemiah core. The C7 was officially launched in May 2005,...
line, while retaining their encryption extensions.
Differences between AMD64 and Intel 64
Although nearly identical, there are some differences between the two instruction sets in the semantics of a few seldom used machine instructions (and/or situations), which are mainly used for
system programmingSystem programming is the activity of programming system software. The primary distinguishing characteristic of systems programming when compared to application programming is that application programming aims to produce software which provides services to the user System programming (or systems...
. Compilers generally produce executables (i.e.
machine codeMachine code or machine language is a system of impartible instructions executed directly by a computer's central processing unit. Each instruction performs a very specific task, typically either an operation on a unit of data Machine code or machine language is a system of impartible instructions...
) that avoid any differences, at least for ordinary application programs. This is therefore of interest mainly to developers of compilers, operating systems and similar, which must deal with individual and special system instructions.
Recent implementations
- Intel 64's BSF and BSR instructions act differently when the source is 0 and the operand size is 32 bits. The processor sets the zero flag and leaves the upper 32 bits of the destination undefined.
- AMD64 requires a different microcode update format and control MSRs (model-specific registers) while Intel 64 implements microcode
Microcode is a layer of hardware-level instructions and/or data structures involved in the implementation of higher level machine code instructions in many computers and other processors; it resides in special high-speed memory and translates machine instructions into sequences of detailed...
update unchanged from their 32-bit only processors.
- Intel 64 lacks some MSRs that are considered architectural in AMD64. These include SYSCFG, TOP_MEM, and TOP_MEM2.
- Intel 64 allows SYSCALL and SYSRET only in 64-bit mode (not in compatibility mode). It allows SYSENTER and SYSEXIT in both modes.
- AMD64 lacks SYSENTER and SYSEXIT in both sub-modes of long mode
In the x86-64 computer architecture, long mode is the mode where a 64-bit application can access 64-bit instructions and registers...
.
- Near branches with the 66H (operand size override) prefix behave differently. Intel 64 clears only the top 32 bits, while AMD64 clears the top 48 bits.
- AMD processors raise a floating point Invalid Exception when performing an FLD or FSTP of an 80-bit signalling NaN, while Intel processors do not.
- Intel 64 lacks the ability to save and restore a reduced (and thus faster) version of the floating-point state (involving the FXSAVE and FXRSTOR instructions).
- Recent AMD64 processors have reintroduced limited support for segmentation to ease virtualization of 64-bit guests.
Older implementations
- Early AMD64 processors lacked the CMPXCHG16B instruction, which is an extension of the CMPXCHG8B instruction present on most post-80486 processors. Similar to CMPXCHG8B, CMPXCHG16B allows for atomic operations on octal words. This is useful for parallel algorithms that use compare and swap on data larger than the size of a pointer, common in lock-free and wait-free algorithms. Without CMPXCHG16B one must use workarounds, such as a critical section
In concurrent programming a critical section is a piece of code that accesses a shared resource that must not be concurrently accessed by more than one thread of execution. A critical section will usually terminate in fixed time, and a thread, task or process will have to wait a fixed time to...
or alternative lock-free approaches.http://www.research.ibm.com/people/m/michael/disc-2004.pdf This also prevents 64-bit WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
from having a user-mode address space larger than 8 terabytes.
- Early AMD64 and Intel 64 CPUs lacked LAHF and SAHF instructions. AMD introduced the instructions with their Athlon 64, Opteron and Turion 64 revision D processors in March 2005 while Intel introduced the instructions with the Pentium 4 G1 stepping in December 2005.
- Early Intel CPUs with Intel 64 also lack the NX bit
The NX bit, which stands for No eXecute, is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions or for storage of data, a feature normally only found in Harvard architecture processors...
of the AMD64 architecture.
- Early Intel 64 implementations only allowed access to 64 GB of physical memory while original AMD64 implementations allowed access to 1 TB of physical memory. Recent AMD64 and Intel 64 implementations provide 256 TB of physical address space (and AMD plans an expansion to 4 PB.) Physical memory capacities of this size are appropriate for large-scale applications (such as large databases), and high-performance computing (centrally oriented applications and scientific computing.)
- AMD64 originally lacked the MONITOR and MWAIT instructions.
Operating system compatibility and characteristics
The following operating systems and releases support the x86-64 architecture in
long modeIn the x86-64 computer architecture, long mode is the mode where a 64-bit application can access 64-bit instructions and registers...
.
DragonFly BSD
Preliminary infrastructure work was started in February 2004 for a x86-64 port. This development later stalled. Development started again during July 2007 and continued during
Google Summer of CodeThe Google Summer of Code is an annual program, first held from May to August 2005, in which Google awards stipends to hundreds of students who successfully complete a requested free or open-source software coding project during the summer...
2008 and SoC 2009. The first official release to contain x86-64 support was version 2.4.
FreeBSD
FreeBSDFreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
first added x86-64 support under the name "amd64" as an experimental architecture in 5.1-RELEASE in June 2003. It was included as a standard distribution architecture as of 5.2-RELEASE in January 2004. Since then, FreeBSD has designated it as a Tier 1 platform. The 6.0-RELEASE version cleaned up some quirks with running x86 executables under amd64, and most drivers work just as they do on the x86 architecture. Work is currently being done to integrate more fully the x86
application binary interfaceIn computer software, an application binary interface describes the low-level interface between an application program and the operating system or another application.- Description :...
(ABI), in the same manner as the Linux 32-bit ABI compatibility currently works.
NetBSD
x86-64 architecture support was first committed to the
NetBSDNetBSD is a freely available open source version of the Berkeley Software Distribution Unix operating system. It was the second open source BSD descendant to be formally released, after 386BSD, and continues to be actively developed. The NetBSD project is primarily focused on high quality design,...
source tree on 19 June 2001. As of NetBSD 2.0, released on 9 December 2004,
NetBSD/amd64 is a fully integrated and supported port.
OpenBSD
OpenBSDOpenBSD is a Unix-like computer operating system descended from Berkeley Software Distribution , a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD by project leader Theo de Raadt in late 1995...
has supported AMD64 since OpenBSD 3.5, released on 1 May 2004. Complete in-tree implementation of AMD64 support was achieved prior to the hardware's initial release due to AMD's loaning of several machines for the project's
hackathonA hackathon, a hacker neologism, is an event when programmers meet to do collaborative computer programming. The spirit of a hackathon is to collaboratively build programs and applications. Hackathons are typically between several days and a week in length...
that year. OpenBSD developers have taken to the platform because of its support for the
NX bitThe NX bit, which stands for No eXecute, is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions or for storage of data, a feature normally only found in Harvard architecture processors...
, which allowed for an easy implementation of the
W^XW^X is the name of a security feature present in the OpenBSD operating system. It is a memory protection policy whereby every page in a process' address space is either writable or executable, but not both simultaneously...
feature.
The code for the AMD64 port of OpenBSD also runs on Intel 64 processors which contains cloned use of the AMD64 extensions, but since Intel left out the page table NX bit in early Intel 64 processors, there is no W^X capability on those Intel CPUs; later Intel 64 processors added the NX bit under the name "XD bit".
Symmetric multiprocessingIn computing, symmetric multiprocessing involves a multiprocessor computer hardware architecture where two or more identical processors are connected to a single shared main memory and are controlled by a single OS instance. Most common multiprocessor systems today use an SMP architecture...
(SMP) works on OpenBSD's AMD64 port, starting with release 3.6 on 1 November 2004.
DOS
It is possible to enter
long modeIn the x86-64 computer architecture, long mode is the mode where a 64-bit application can access 64-bit instructions and registers...
under
DOSDOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
without a DOS extender, but the user must return to real mode in order to call BIOS or DOS interrupts.
It may also be possible to enter
long modeIn the x86-64 computer architecture, long mode is the mode where a 64-bit application can access 64-bit instructions and registers...
with a
DOS extenderA DOS extender is a computer software program which enables software to run under a protected mode environment even though the host operating system is only capable of operating in real mode....
similar to
DOS/4GWDOS/4G is a 32-bit DOS extender developed by Rational Systems . It allows DOS programs to eliminate the 640 KB conventional memory limit by addressing up to 64 MB of extended memory on Intel 80386 and above machines....
, but more complex since x86-64 lacks
virtual 8086 modeIn the 80386 microprocessor and later, virtual 8086 mode allows the execution of real mode applications that are incapable of running directly in protected mode while the processor is running a protected mode operating system.VM86 mode uses a segmentation scheme identical to that of real mode In...
. DOS itself is not aware of that, and no benefits should be expected unless running DOS in an emulation with an adequate virtualization driver backend, for example: the mass storage interface.
Linux
LinuxLinux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
was the first operating system kernel to run the x86-64 architecture in
long modeIn the x86-64 computer architecture, long mode is the mode where a 64-bit application can access 64-bit instructions and registers...
, starting with the 2.4 version in 2001 (prior to the physical hardware's availability). Linux also provides backward compatibility for running 32-bit executables. This permits programs to be recompiled into long mode while retaining the use of 32-bit programs. Several Linux distributions currently ship with x86-64-native kernels and userlands. Some, such as SUSE,
MandrivaMandriva Linux is a Linux distribution distributed by Mandriva. It uses the RPM Package Manager...
, and
Debian GNU/LinuxDebian is a computer operating system composed of software packages released as free and open source software primarily under the GNU General Public License along with other free software licenses. Debian GNU/Linux, which includes the GNU OS tools and Linux kernel, is a popular and influential...
, allow users to install a set of 32-bit components and libraries when installing off a 64-bit DVD, thus allowing most existing 32-bit applications to run alongside the 64-bit OS. Other distributions, such as
FedoraFedora is a RPM-based, general purpose collection of software, including an operating system based on the Linux kernel, developed by the community-supported Fedora Project and sponsored by Red Hat...
,
SlackwareSlackware is a free and open source Linux-based operating system. It was one of the earliest operating systems to be built on top of the Linux kernel and is the oldest currently being maintained. Slackware was created by Patrick Volkerding of Slackware Linux, Inc. in 1993...
,
UbuntuUbuntu is a computer operating system based on the Debian Linux distribution and distributed as free and open source software. It is named after the Southern African philosophy of Ubuntu...
, and
Arch LinuxArch Linux is an independently developed, Linux-based operating system for i686 and x86-64 computers. It is composed predominantly of free and open source software, and supports community involvement....
, are available in one version compiled for a 32-bit architecture and another compiled for a 64-bit architecture. Fedora and RedHat Enterprise Linux allow concurrent installation of all userland components in both 32 and 64-bit versions on a 64-bit system.
x32 ABI (Application Binary Interface) is an under development Linux project that allows programs compiled for the x32 ABI to run in the 64-bit mode of x86-64 while only using 32-bit pointers and data fields. Though this limits the program to a virtual address space of 4 GB it also decreases the memory footprint of the program and in some cases can allow it to run faster.
64-bit
DebianDebian is a computer operating system composed of software packages released as free and open source software primarily under the GNU General Public License along with other free software licenses. Debian GNU/Linux, which includes the GNU OS tools and Linux kernel, is a popular and influential...
Linux allows up to 128
TBThe terabyte is a multiple of the unit byte for digital information. The prefix tera means 1012 in the International System of Units , and therefore 1 terabyte is , or 1 trillion bytes, or 1000 gigabytes. 1 terabyte in binary prefixes is 0.9095 tebibytes, or 931.32 gibibytes...
of virtual address space for individual processes, and can address approximately 64 TB of physical memory, subject to processor and system limitations.
Mac OS X
Mac OS X v10.4.7 and higher versions of
Mac OS X v10.4Mac OS X v10.4 Tiger is the fifth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. Tiger was released to the public on 29 April 2005 for US$129.95 as the successor to Mac OS X Panther , which had been released 18 months earlier...
run 64-bit command-line tools using the POSIX and math libraries on 64-bit Intel-based machines, just as all versions of Mac OS X v10.4 and 10.5 run them on 64-bit PowerPC machines. No other libraries or frameworks work with 64-bit applications in Mac OS X v10.4. The kernel, and all kernel extensions, are 32-bit only.
Mac OS X v10.5Mac OS X Leopard is the sixth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. Leopard was released on 26 October 2007 as the successor of Tiger , and is available in two variants: a desktop version suitable for personal computers, and a...
supports 64-bit GUI applications using
CocoaCocoa is Apple's native object-oriented application programming interface for the Mac OS X operating system and—along with the Cocoa Touch extension for gesture recognition and animation—for applications for the iOS operating system, used on Apple devices such as the iPhone, the iPod Touch, and...
,
QuartzQuartz specifically refers to a pair of Mac OS X technologies, each part of the Core Graphics framework: Quartz 2D and Quartz Compositor. It includes both a 2D renderer in Core Graphics and the composition engine that sends instructions to the graphics card...
,
OpenGLOpenGL is a standard specification defining a cross-language, cross-platform API for writing applications that produce 2D and 3D computer graphics. The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes from simple primitives. OpenGL...
, and X11 on 64-bit Intel-based machines, as well as on 64-bit
PowerPCPowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM...
machines. All non-GUI libraries and frameworks also support 64-bit applications on those platforms. The kernel, and all kernel extensions, are 32-bit only.
Mac OS X v10.6Mac OS X Snow Leopard is the seventh major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers.Snow Leopard was publicly unveiled on June 8, 2009 at the Apple Worldwide Developers Conference...
is the first version of Mac OS X that supports a 64-bit
kernelIn computing, the kernel is the main component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources...
. However, with its first release (v10.6.0), not all 64-bit computers are currently supported. The 64-bit kernel, like the 32-bit kernel, supports 32-bit applications; both kernels also support 64-bit applications. 32-bit applications have a virtual address space limit of 4 GB under either kernel.
The 64-bit kernel does not support 32-bit
kernel extensionsIn computing, a loadable kernel module is an object file that contains code to extend the running kernel, or so-called base kernel, of an operating system...
, and the 32-bit kernel does not support 64-bit kernel extensions.
Mac OS X uses the
universal binaryA universal binary is, in Apple parlance, an executable file or application bundle that runs natively on either PowerPC or Intel-manufactured IA-32 or Intel 64-based Macintosh computers; it is an implementation of the concept more generally known as a fat binary.With the release of Mac OS X Snow...
format to package 32- and 64-bit versions of application and library code into a single file; the most appropriate version is automatically selected at load time. In Mac OS X 10.6, the universal binary format is also used for the kernel and for those kernel extensions that support both 32-bit and 64-bit kernels.
Mac OS X v10.7 runs the 64-bit kernel by default on supported machines. Older machines that cannot run the 64-bit kernel run the 32-bit kernel. Both seamlessly support 32- and 64-bit applications.
Solaris
SolarisSolaris is a Unix operating system originally developed by Sun Microsystems. It superseded their earlier SunOS in 1993. Oracle Solaris, as it is now known, has been owned by Oracle Corporation since Oracle's acquisition of Sun in January 2010....
10 and later releases support the x86-64 architecture. Just as with the
SPARCSPARC is a RISC instruction set architecture developed by Sun Microsystems and introduced in mid-1987....
architecture, there is only one operating system image for all 32-bit and 64-bit x86 systems; this is labeled as the "x64/x86" DVD-ROM image.
Default behavior is to boot a 64-bit kernel, allowing both 64-bit and existing or new 32-bit executables to be run. A 32-bit kernel can also be manually selected, in which case only 32-bit executables will run. The
isainfo command can be used to determine if a system is running a 64-bit kernel.
Windows
x86-64 editions of Microsoft Windows client and server, Windows XP Professional x64 Edition and
Windows Server 2003Windows Server 2003 is a server operating system produced by Microsoft, introduced on 24 April 2003. An updated version, Windows Server 2003 R2, was released to manufacturing on 6 December 2005...
x64 Edition were released in March 2005. Internally they are actually the same build (5.2.3790.1830 SP1), as they share the same source base and operating system binaries, so even system updates are released in unified packages, much in the manner as Windows 2000 Professional and Server editions for x86.
Windows VistaWindows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
, which also has many different editions, was released in January 2007. Windows 7 was released in July 2009.
Windows Server 2008 R2Windows Server 2008 R2 is a server operating system produced by Microsoft. It was released to manufacturing on July 22, 2009 and launched on October 22, 2009. According to the Windows Server Team blog, the retail availability was September 14, 2009. It is built on Windows NT 6.1, the same core...
and later versions will only be available as x86-64 versions. Windows for x86-64 has the following characteristics:
- 8 TB of "user mode" virtual address space per process. A 64-bit program can use all of this, subject of course to backing-store limits on the system, and provided it is linked with the "large address aware" option. This is a 4096-fold increase over the default 2 GB user-mode virtual address space offered by 32-bit Windows.
- 8 TB of kernel mode virtual address space for the operating system. As with the user mode address space, this is a 4096-fold increase over 32-bit Windows versions. The increased space primarily benefits the file-system cache and kernel-mode "heaps" (non-paged pool and paged pool). Windows only uses a total of 16 TB out of the 256 TB implemented by the processors because early AMD64 processors lacked a CMPXCHG16B instruction.
- Ability to run existing 32-bit applications (
.exe programs) and dynamic link libraries (.dlls) using WoW64WoW64 is a subsystem of the Windows operating system that is capable of running 32-bit applications and is included on all 64-bit versions of Windows—including Windows XP Professional x64 Edition, IA-64 and x64 versions of Windows Server 2003, as well as 64-bit versions of Windows Vista, Windows...
. Furthermore, a 32-bit program, if it was linked with the "large address aware" option, can use up to 4 GB of virtual address space in 64-bit Windows, instead of the default 2 GB (optional 3 GB with /3GB boot option and "large address aware" link option) offered by 32-bit Windows. Unlike the use of the /3GB boot option on x86, this does not reduce the kernel-mode virtual-address space available to the operating system. 32-bit applications can therefore benefit from running on x64 Windows even if they are not recompiled for x86-64.
- Both 32- and 64-bit applications, if not linked with "large address aware," are limited to 2 GB of virtual address space.
- Ability to use up to 128 GB (Windows XP/Vista), 192 GB (Windows 7), 1 TB (Windows Server 2003), or 2 TB (Windows Server 2008) of physical random access memory (RAM).
- LLP64
64-bit is a word size that defines certain classes of computer architecture, buses, memory and CPUs, and by extension the software that runs on them. 64-bit CPUs have existed in supercomputers since the 1970s and in RISC-based workstations and servers since the early 1990s...
data model: "int" and "long" types are 32 bits wide, long long is 64 bits, while pointers and types derived from pointers are 64 bits wide.
- Kernel-mode device drivers must be 64-bit versions; there is no way to run 32-bit kernel-mode executables within the 64-bit operating system. User mode device drivers can be either 32-bit or 64-bit.
- 16-bit Windows (Win16) and DOS applications will not run on x86-64 versions of Windows due to removal of the virtual DOS machine
Virtual DOS machine is Microsoft's technology that allows running legacy DOS and 16-bit Windows programs on Intel 80386 or higher computers when there is already another operating system running and controlling the hardware.-Overview:...
subsystem (NTVDM) which relied upon the ability to use virtual 8086 mode. Virtual 8086 mode cannot be entered while running in long mode.
- Full implementation of the NX
The NX bit, which stands for No eXecute, is a technology used in CPUs to segregate areas of memory for use by either storage of processor instructions or for storage of data, a feature normally only found in Harvard architecture processors...
(No Execute) page protection feature. This is also implemented on recent 32-bit versions of Windows when they are started in PAE mode.
- Instead of FS segment descriptor on x86 versions of the Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
family, GS segment descriptor is used to point to two operating system defined structures: Thread Information Block (NT_TIB) in user mode and Processor Control Region (KPCR) in kernel mode. Thus, for example, in user mode GS:0 is the address of the first member of the Thread Information Block. Maintaining this convention made the x86-64 port easier, but required AMD to retain the function of the FS and GS segments in long mode — even though segmented addressing per se is not really used by any modern operating system.
- Early reports claimed that the operating system scheduler would not save and restore the x87 FPU machine state across thread context switches. Observed behavior shows that this is not the case: the x87 state is saved and restored, except for kernel-mode-only threads (a limitation that exists in the 32-bit version as well). The most recent documentation available from Microsoft states that the x87/MMX/3DNow! instructions may be used in long mode, but that they are deprecated and may cause compatibility problems in the future.
- Some components like Microsoft Jet Database Engine
The Microsoft Jet Database Engine is a database engine on which several Microsoft products have been built. A database engine is the underlying component of a database, a collection of information stored on a computer in a systematic way...
and Data Access ObjectsJet Data Access Objects is a deprecated general programming interface for database access on Microsoft Windows systems. It is unrelated to the data access object design pattern used in object-oriented software design.- History :...
will not be ported to 64-bit architectures such as x86-64 and IA-64.
- Microsoft Visual Studio
Microsoft Visual Studio is an integrated development environment from Microsoft. It is used to develop console and graphical user interface applications along with Windows Forms applications, web sites, web applications, and web services in both native code together with managed code for all...
can compile native applications to target either the x86-64 architecture, which can run only on 64-bit Microsoft Windows, or the IA-32IA-32 , also known as x86-32, i386 or x86, is the CISC instruction-set architecture of Intel's most commercially successful microprocessors, and was first implemented in the Intel 80386 as a 32-bit extension of x86 architecture...
architecture, which can run as a 32-bit application on 32-bit Microsoft Windows or 64-bit Microsoft Windows in WoW64WoW64 is a subsystem of the Windows operating system that is capable of running 32-bit applications and is included on all 64-bit versions of Windows—including Windows XP Professional x64 Edition, IA-64 and x64 versions of Windows Server 2003, as well as 64-bit versions of Windows Vista, Windows...
emulation mode. Managed applicationManaged code is a term coined by Microsoft to identify computer program code that requires and will only execute under the "management" of a Common Language Runtime virtual machine ....
s can be compiled either in IA-32, x86-64 or AnyCPU modes. Software created in the first two modes behave like their IA-32 or x86-64 native code counterparts respectively; When using the AnyCPU mode however, applications in 32-bit versions of Microsoft Windows run as 32-bit applications, while they run as a 64-bit application in 64-bit editions of Microsoft Windows.
Industry naming conventions
Since AMD64 and Intel 64 are substantially similar, many software and hardware products use one vendor-neutral term to indicate their compatibility with both implementations. AMD's original designation for this processor architecture, "x86-64", is still sometimes used for this purpose, as is the variant "x86_64". Other companies, such as
MicrosoftMicrosoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
and
Sun MicrosystemsSun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
, use the contraction "x64" in marketing material.
The term IA-64 refers to the
ItaniumItanium is a family of 64-bit Intel microprocessors that implement the Intel Itanium architecture . Intel markets the processors for enterprise servers and high-performance computing systems...
processor, and should not be confused with x86-64, as it is a completely different instruction set.
Many operating systems and products, especially those that introduced x86-64 support prior to Intel's entry into the market, use the term "AMD64" or "amd64" to refer to both AMD64 and Intel 64.
- BSD systems such as FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
, MidnightBSDMidnightBSD is a free Unix-like, desktop-oriented operating system based on FreeBSD 6.1. It borrows heavily from the NEXTSTEP graphical user interface.- History and development :...
, NetBSDNetBSD is a freely available open source version of the Berkeley Software Distribution Unix operating system. It was the second open source BSD descendant to be formally released, after 386BSD, and continues to be actively developed. The NetBSD project is primarily focused on high quality design,...
and OpenBSDOpenBSD is a Unix-like computer operating system descended from Berkeley Software Distribution , a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD by project leader Theo de Raadt in late 1995...
refer to both AMD64 and Intel 64 under the architecture name "amd64".
- The Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
kernel and DragonFly BSDDragonFly BSD is a free Unix-like operating system created as a fork of FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and a FreeBSD developer between 1994 and 2003, began work on DragonFly BSD in June 2003 and announced it on the FreeBSD mailing lists on July...
refers to 64-bit architecture as "x86_64".
- The GNU Compiler Collection
The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...
refers to 64-bit architecture as "amd64".
- Debian
Debian is a computer operating system composed of software packages released as free and open source software primarily under the GNU General Public License along with other free software licenses. Debian GNU/Linux, which includes the GNU OS tools and Linux kernel, is a popular and influential...
, UbuntuUbuntu is a computer operating system based on the Debian Linux distribution and distributed as free and open source software. It is named after the Southern African philosophy of Ubuntu...
, and GentooGentoo Linux is a computer operating system built on top of the Linux kernel and based on the Portage package management system. It is distributed as free and open source software. Unlike a conventional software distribution, the user compiles the source code locally according to their chosen...
refer to both AMD64 and Intel 64 under the architecture name "amd64".
- Fedora
Fedora is a RPM-based, general purpose collection of software, including an operating system based on the Linux kernel, developed by the community-supported Fedora Project and sponsored by Red Hat...
, PackageKitPackageKit is an open source and free suite of software applications designed to provide a consistent and high-level front end for a number of different package management systems...
, openSUSEopenSUSE is a general purpose operating system built on top of the Linux kernel, developed by the community-supported openSUSE Project and sponsored by SUSE...
, and Arch LinuxArch Linux is an independently developed, Linux-based operating system for i686 and x86-64 computers. It is composed predominantly of free and open source software, and supports community involvement....
refer to 64-bit architecture as "x86_64".
- Haiku
Haiku is a free and open source operating system compatible with BeOS. Its development began in 2001, and the operating system became self-hosting in 2008, with the first alpha release in September 2009, the second in May 2010 and the third in June 2011....
: refers to 64-bit architecture as "x86_64".
- Java Development Kit
The Java Development Kit is an Oracle Corporation product aimed at Java developers. Since the introduction of Java, it has been by far the most widely used Java SDK. On 17 November 2006, Sun announced that it would be released under the GNU General Public License , thus making it free software...
(JDK): The name "amd64" is used in directory names containing x86-64 files.
- Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
: Apple refers to 64-bit architecture as "x86_64", as noted with the Terminal command arch and in their developer documentation. http://developer.apple.com/documentation/Darwin/Reference/ManPages/man1/arch.1.html
- Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
: x86-64 versions of Windows use the AMD64 moniker internally to designate various components which use or are compatible with this architecture. For example, the system directory on a Windows x86-64 Edition installation CD-ROM is named "AMD64", in contrast to "i386" in 32-bit versions.
- Solaris: The "isalist" command in Sun's Solaris operating system identifies both AMD64- and Intel 64–based systems as "amd64".
- T2 SDE refer to both AMD64 and Intel 64 under the architecture name "x86-64", in source code directories and package meta information.
Legal issues
AMD
licenseThe verb license or grant licence means to give permission. The noun license or licence refers to that permission as well as to the document recording that permission.A license may be granted by a party to another party as an element of an agreement...
d its x86-64 design to Intel, where it is marketed under the name
Intel 64. As Intel licenses AMD the right to use the original x86 architecture (upon which AMD's x86-64 is based), these rival companies now rely on each other for 64-bit processor development. Should this agreement collapse, AMD would no longer be authorized to produce any x86 processors, and Intel would no longer be authorized to produce x86-64 processors, forcing it back to the x86 architecture. However, the agreement provides that if one party breaches the agreement, it loses all rights to the other party's technology, while the other party receives perpetual rights to all licensed technology.
In 2009, AMD and Intel settled several lawsuits and cross-licensing disagreements, extending their cross-licensing agreements for the foreseeable future and settling several anti-trust complaints.
External links