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64-bit CPUs have existed in supercomputers since the 1960s and in RISC-based workstations and server
Server (computing)

A server is a computer program that provides services to other computer programs , in the same or other computer. The physical computer that runs a server program is also often referred to as server....
s since the early 1990s. In 2003 they were introduced to the (previously 32-bit
32-bit

The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295 or -2,147,483,648 through 2,147,483,647 using two's complement encoding....
) mainstream personal computer
Personal computer

A personal computer is any general-purpose computer whose original sales price, size, and capabilities make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator....
 arena, in the form of the x86-64
X86-64

x86-64 is a superset of the x86. x86-64 Central processing units can run existing 32-bit or 16-bit x86 programs at full speed, but also support new programs written with a 64-bit address space and other additional capabilities....
 and 64-bit PowerPC
PowerPC

PowerPC is a RISC instruction set architecture created by the 1991 Apple Inc.?IBM?Motorola alliance, known as AIM alliance. Originally intended for personal computers, PowerPC CPUs have since become popular embedded system and high-performance processors....
 processor architectures.

Without further qualification, a 64-bit computer architecture generally has integer and addressing registers
Processor register

In computer architecture, a processor register is a small amount of Computer storage available on the CPU whose contents can be accessed more quickly than storage available elsewhere....
 that are 64 bits wide, allowing direct support for 64-bit data types and addresses.






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64-bit CPUs have existed in supercomputers since the 1960s and in RISC-based workstations and server
Server (computing)

A server is a computer program that provides services to other computer programs , in the same or other computer. The physical computer that runs a server program is also often referred to as server....
s since the early 1990s. In 2003 they were introduced to the (previously 32-bit
32-bit

The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295 or -2,147,483,648 through 2,147,483,647 using two's complement encoding....
) mainstream personal computer
Personal computer

A personal computer is any general-purpose computer whose original sales price, size, and capabilities make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator....
 arena, in the form of the x86-64
X86-64

x86-64 is a superset of the x86. x86-64 Central processing units can run existing 32-bit or 16-bit x86 programs at full speed, but also support new programs written with a 64-bit address space and other additional capabilities....
 and 64-bit PowerPC
PowerPC

PowerPC is a RISC instruction set architecture created by the 1991 Apple Inc.?IBM?Motorola alliance, known as AIM alliance. Originally intended for personal computers, PowerPC CPUs have since become popular embedded system and high-performance processors....
 processor architectures.

Without further qualification, a 64-bit computer architecture generally has integer and addressing registers
Processor register

In computer architecture, a processor register is a small amount of Computer storage available on the CPU whose contents can be accessed more quickly than storage available elsewhere....
 that are 64 bits wide, allowing direct support for 64-bit data types and addresses. However, a CPU might have external data buses or address bus
Address bus

An address bus is a computer bus that is used to specify a memory address. When a central processing unit or direct memory access-enabled device needs to read or write to a memory location, it specifies that memory location on the address bus ....
es with different sizes than the registers, even larger (the 32-bit Pentium
Pentium

Introduced on March 22, 1993, the original Pentium was the first superscalar x86 architecture microprocessor. Its fifth-generation x86 microarchitecture was a direct extension of the 80486 architecture with dual integer pipeline s, a faster FPU unit, wider data bus, and features for further reduced address calculation latency....
 had a 64-bit data bus, for instance). The term may also refer to the size of low-level data types, such as 64-bit floating-point
Floating point

In computing, floating point describes a system for numerical representation in which a String of digits represents a rational number.The term floating point refers to the fact that the radix point can "float": that is, it can be placed anywhere relative to the Significant figures of the number....
 numbers.

Architectural implications

Processor registers are typically divided into several groups: integer, floating-point, SIMD
SIMD

In computing, SIMD is a technique employed to achieve data level parallelism....
, control, and often special registers for address arithmetic which may have various uses and names such as address, index or base registers. However, in modern designs, these functions are often performed by more general purpose integer registers. In most processors, only integer and/or address-registers can be used to address data in memory, the other types cannot. The size of these registers therefore normally limit the amount of directly addressable memory, even if there are registers, such as floating-point registers, that are wider.

Most high performance 32-bit and 64-bit processors (some notable exceptions are most ARM
ARM architecture

The ARM architecture is a 32-bit RISC central processing unit architecture developed by ARM Limited that is widely used in embedded system designs....
 and 32-bit MIPS
MIPS architecture

MIPS is a RISC instruction set architecture developed by MIPS Technologies . In the mid to late 1990s, it was estimated that one in three RISC microprocessors produced were MIPS implementations....
 CPUs) have integrated floating point hardware, which is often but not always, based on 64-bit units of data. For example, although the x86/x87
X87

x87 is a math-related instruction subset of the x86 architecture of Central processing unit. It is so called because initially such instructions were processed by an coprocessor#Intel coprocessors chip 8087....
 architecture has instructions capable of loading and storing 64-bit (and 32-bit) floating-point values in memory, the internal data and register format is 80-bit wide. In contrast, the 64-bit Alpha
DEC Alpha

Alpha, originally known as Alpha AXP, was a 64-bit reduced instruction set computer instruction set architecture developed by Digital Equipment Corporation , designed to replace the 32-bit VAX complex instruction set computer ISA and its implementations....
 family uses a 64-bit floating-point data and register format (as well as 64-bit integer registers).

History

Most CPUs are designed so that the contents of a single integer register can store the address
Memory address

In computer science, a memory address is an identifier for a computer memory location, at which a computer program or a hardware device can store a piece of data and later retrieve it....
 (location) of any datum in the computer's virtual memory
Virtual memory

Virtual memory is a computer system technique which gives an application program the impression that it has contiguous working memory , while in fact it may be physically fragmented and may even overflow on to disk storage....
. Therefore, the total number of addresses in the virtual memory — the total amount of data the computer can keep in its working area — is determined by the width of these registers. Beginning in the 1960s with the IBM
IBM

International Business Machines Corporation, abbreviated IBM and nicknamed "Big Blue" , is a multinational corporation computer technology and consulting corporation headquartered in Armonk, New York, New York, United States....
 System/360
System/360

The IBM System/360 is a mainframe computer system family announced by IBM on April 7, 1964. It was the first family of computers making a clear distinction between computer architecture and implementation, allowing IBM to release a suite of compatible designs at different price points....
, then (amongst many others) the DEC
Digital Equipment Corporation

Digital Equipment Corporation was a pioneering United States company in the computer industry. It is often referred to within the computing industry as DEC ....
 VAX
VAX

VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs....
 minicomputer in the 1970s, and then with the Intel 80386
Intel 80386

The Intel 80386, otherwise known as the i386 or just 386, is a microprocessor which has been used as the central processing unit of many personal computers and workstations since 1986....
 in the mid-1980s, a de facto consensus developed that 32 bits was a convenient register size. A 32-bit address register meant that 232 addresses, or 4 GB
Gigabyte

Gigabyte is an SI prefix-multiple of the unit byte for Computer data storage. Since the giga- prefix means 109, gigabyte means 1,000,000,000 bytes ....
 of RAM, could be referenced. At the time these architectures were devised, 4 GB of memory was so far beyond the typical quantities (16 MB) available in installations that this was considered to be enough "headroom" for addressing. 4 GB addresses were considered an appropriate size to work with for another important reason: 4 billion integers are enough to assign unique references to most physically countable things in applications like database
Database

A database is a structured collection of records or data that is stored in a computer system. The structure is achieved by organizing the data according to a database model....
s.

Some supercomputer
Supercomputer

A supercomputer is a computer that is at the frontline of current processing capacity, particularly speed of calculation. Supercomputers introduced in the 1960s were designed primarily by Seymour Cray at Control Data Corporation , and led the market into the 1970s until Cray left to form his own company, Cray Research....
 processor architectures of the 1970s and 80s used registers up to 64 bits wide. However, 32 bits remained the norm until the early 1990s, when the continual reductions in the cost of memory led to installations with quantities of RAM approaching 4 GB, and the use of virtual memory spaces exceeding the 4-gigabyte ceiling became desirable for handling certain types of problems. In response, MIPS and DEC developed 64-bit microprocessor architectures, initially for high-end workstation
Workstation

A workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems....
 and server
Server (computing)

A server is a computer program that provides services to other computer programs , in the same or other computer. The physical computer that runs a server program is also often referred to as server....
 machines. By the mid-1990s, HAL Computer Systems
HAL Computer Systems

HAL Computer Systems, Inc was a Campbell, California-based computer manufacturer. It was founded in 1990 by Andrew Heller, a principal designer of the original IBM POWER architecture....
, Sun Microsystems
Sun Microsystems

Sun Microsystems, Inc. is a multinational corporation vendor of computers, computer components, computer software, and information technology services, founded on February 24, 1982....
, IBM
IBM

International Business Machines Corporation, abbreviated IBM and nicknamed "Big Blue" , is a multinational corporation computer technology and consulting corporation headquartered in Armonk, New York, New York, United States....
 and Hewlett Packard had developed 64-bit architectures for their workstation and server systems. A notable exclusion to this trend were mainframes
Mainframe computer

Mainframes are computers used mainly by large organizations for critical applications, typically bulk data processing such as census, industry and consumer statistics, Enterprise Resource Planning, and financial transaction processing....
 from IBM, which remained 32-bit. During the 1990s, several low-cost 64-bit microprocessors were used in consumer electronics and embedded applications. Notably, the Nintendo 64
Nintendo 64

The , often abbreviated as N64, is Nintendo's third home video game console for the international market. Named for its 64-bit CPU, it was released on June 23, 1996 in Japan, September 29, 1996 in North America, March 1, 1997 in Europe and Australia, September 1, 1997 in France and December 10, 1997 in Brazil....
 and PlayStation 2
PlayStation 2

The PlayStation 2 is a History of video game consoles video game console manufactured by Sony. The successor to the PlayStation, and the predecessor to the PlayStation 3, the PlayStation 2 forms part of the PlayStation of video game consoles....
 both had 64-bit microprocessors before its introduction in personal computers. High-end printers and network equipment, as well as industrial computers also used 64-bit microprocessors such as the Quantum Effect Devices
Quantum Effect Devices

Quantum Effect Devices was a company originally named Quantum Effect Design, incorporated in 1991. The three founders, Tom Riordan, Earl Killian and Ray Kunita, were senior managers at MIPS Computer Systems Inc.....
 R5000. 64-bit computing started to drift down to the personal computer desktop from 2003 onwards, when some models in Apple's Macintosh lines switched to PowerPC 970
PowerPC 970

The PowerPC 970, PowerPC 970FX, PowerPC 970GX, and PowerPC 970MP, are 64-bit Power Architecture central processing unit from IBM introduced in 2002....
 processors (termed "G5" by Apple) and the launch of AMD
Advanced Micro Devices

Advanced Micro Devices, Inc. is an United States multinational corporation semiconductor industry company based in Sunnyvale, California, that develops Central processing unit and related technologies for commercial and consumer markets....
's 64-bit x86-64
X86-64

x86-64 is a superset of the x86. x86-64 Central processing units can run existing 32-bit or 16-bit x86 programs at full speed, but also support new programs written with a 64-bit address space and other additional capabilities....
 extension to the x86 architecture, processors based on this architecture becoming common in high-end PC
IBM PC

The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform ....
s.

The emergence of the 64-bit architecture effectively increases the memory ceiling to 264 addresses, equivalent to approximately 17.2 billion gigabytes, 16.8 million terabyte
Terabyte

A terabyte is a measurement term for computer storage. The value of a terabyte based upon a decimal radix is defined as one 1000000000000 bytes, or 1000 gigabytes....
s, or 16 exabyte
Exabyte

An exabyte is a unit of information or computer storage equal to one quintillion bytes. It is commonly abbreviated EB. When used with byte multiples, the SI prefix may indicate a power of either 1000 or 1024, so the exact number may be either:...
s of RAM. To put this in perspective, in the days when 4 MB
Megabyte

Megabyte is a SI prefix-multiple of the unit byte for digital information computer storage or transmission and is equal to 106 bytes....
 of main memory was commonplace, the maximum memory ceiling of 232 addresses was about 1,000 times larger than typical memory configurations. Today, when over 2 GB
Gigabyte

Gigabyte is an SI prefix-multiple of the unit byte for Computer data storage. Since the giga- prefix means 109, gigabyte means 1,000,000,000 bytes ....
 of main memory is common, the ceiling of 264 addresses is about ten trillion times larger, i.e., ten billion times more headroom than the 232 case.

Limitations

Most 64-bit microprocessors on the market today have an artificial limit on the amount of memory they can address, because physical constraints make impossible to support the full 16.8 million terabyte capacity. For example, the AMD Athlon X2 has a 40-bit address bus and recognizes only 48 bits of the 64-bit virtual address. The newer Barcelona X4 supports a 48-bit of physical address and 48 bits of the 64-bit virtual address.

64-bit processor timeline


  • 1961: IBM delivers the IBM 7030 Stretch supercomputer
    Supercomputer

    A supercomputer is a computer that is at the frontline of current processing capacity, particularly speed of calculation. Supercomputers introduced in the 1960s were designed primarily by Seymour Cray at Control Data Corporation , and led the market into the 1970s until Cray left to form his own company, Cray Research....
    , which uses 64-bit data words and 32- or 64-bit instruction words.


  • 1974: Control Data Corporation
    Control Data Corporation

    Control Data Corporation was one of the pioneering supercomputer firms. For most of the 1960s, it built the fastest computers in the world by far, only losing that crown in the 1970s to what was effectively a spinoff, after Seymour Cray left the company to found Cray Research, Inc....
     launches the CDC Star-100
    CDC STAR-100

    The STAR-100 was a supercomputer from Control Data Corporation , one of the first machines to use a vector processor for improved math performance....
     vector supercomputer, which uses a 64-bit word architecture (previous CDC systems were based on a 60-bit architecture).


  • 1974: International Computers Limited launches the ICL 2900 Series
    ICL 2900 Series

    The ICL 2900 Series was a range of mainframe computer computer systems announced by the UK manufacturer International Computers Limited on 9 October 1974....
     with 32-bit, 64-bit, and 128-bit twos-complement integers; 64-bit and 128-bit floating point; 32-bit, 64-bit and 128-bit packed decimal and a 128-bit accumulator register. The architecture has survived through a succession of ICL and Fujitsu machines. The latest is the Fujitsu Supernova, which emulates the original environment on 64-bit Intel processors.


  • 1976: Cray Research delivers the first Cray-1
    Cray-1

    The Cray-1 was a supercomputer designed by a team including Seymour Cray for Cray Research. The first Cray-1 system was installed at Los Alamos National Laboratory in 1976, and it went on to become one of the best known and most successful supercomputers in history....
     supercomputer, which is based on a 64-bit word architecture and would form the basis for later Cray vector supercomputers.


  • 1983: Elxsi
    Elxsi

    Elxsi was a minicomputer manufacturing company established in the late 1970s along with a host of other competitors . The Elxsi processor was an Emitter Coupled Logic design that featured a 50 nanosecond clock, a 25 nanosecond backpanel bus, IEEE floating point arithmetic and a 64-bit architecture....
     launches the Elxsi 6400 parallel minisupercomputer
    Minisupercomputer

    Minisupercomputers constituted a class of computers that emerged in the mid-1980s. As scientific computing using vector processors became more popular, the need for lower-cost systems that might be used at the departmental level instead of the corporate level created an opportunity for new computer vendors to enter the market....
    . The Elxsi architecture has 64-bit data registers but a 32-bit address space.


  • 1991: MIPS Technologies
    MIPS Technologies

    MIPS Technologies, Inc. , formerly MIPS Computer Systems, is most widely known for developing the MIPS architecture and a series of pioneering Reduced instruction set computer Central processing unit....
     produces the first 64-bit microprocessor, the R4000, which implements the MIPS III ISA, the third revision of their MIPS architecture
    MIPS architecture

    MIPS is a RISC instruction set architecture developed by MIPS Technologies . In the mid to late 1990s, it was estimated that one in three RISC microprocessors produced were MIPS implementations....
    . The CPU is used in SGI
    Silicon Graphics

    Silicon Graphics, Inc. is a company manufacturer high-performance computing solutions, including computer hardware and computer software. SGI was founded by James H....
     graphics workstations starting with the IRIS Crimson
    SGI Crimson

    The IRIS Crimson, code named Diehard2, is a Silicon Graphics computer released in the early 1990s. It was the world's first 64-bit workstation....
    . However, 64-bit support for the R4000 would not be included in the IRIX
    IRIX

    IRIX is a computer operating system developed by Silicon Graphics, Inc. to run natively on their 32- and 64-bit MIPS architecture workstations and servers....
     operating system
    Operating system

    An operating system is an interface between hardware and applications; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer....
     until IRIX 6.2, released in 1996. Kendall Square Research
    Kendall Square Research

    Kendall Square Research was a supercomputer company headquartered originally in Kendall Square in Cambridge, Massachusetts in 1986, near Massachusetts Institute of Technology....
     deliver their first KSR1 supercomputer, based on a proprietary 64-bit RISC processor architecture running OSF/1.


  • 1992: Digital Equipment Corporation
    Digital Equipment Corporation

    Digital Equipment Corporation was a pioneering United States company in the computer industry. It is often referred to within the computing industry as DEC ....
     (DEC) introduces the pure 64-bit Alpha
    DEC Alpha

    Alpha, originally known as Alpha AXP, was a 64-bit reduced instruction set computer instruction set architecture developed by Digital Equipment Corporation , designed to replace the 32-bit VAX complex instruction set computer ISA and its implementations....
     architecture which was born from the PRISM
    DEC PRISM

    PRISM was a 32-bit RISC Central processing unit design from Digital Equipment Corporation . It was the final outcome of a number of DEC-internal research projects from the 1982-1985 time-frame, and was at the point of delivering silicon in 1988 when the management canceled the project....
     project.


  • 1993: DEC releases the 64-bit DEC OSF/1 AXP Unix-like
    Unix-like

    A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
     operating system (later renamed Tru64 UNIX).


  • 1994: Intel announces plans for the 64-bit IA-64 architecture (jointly developed with Hewlett-Packard
    Hewlett-Packard

    The Hewlett-Packard Company , commonly referred to as HP, is a technology corporation headquartered in Palo Alto, California, United States....
    ) as a successor to its 32-bit IA-32
    IA-32

    IA-32 , often generically called x86 or x86-32, is the instruction set architecture of Intel's most commercially successful microprocessors....
     processors. A 1998 to 1999 launch date is targeted. SGI releases IRIX 6.0, with 64-bit support for the R8000
    R8000

    The R8000 is a microprocessor chip set implementing the MIPS architecture instruction set architecture jointly developed by MIPS Technologies , then a subsidiary of Silicon Graphics, Inc....
     chip set.


  • 1995: Sun
    Sun Microsystems

    Sun Microsystems, Inc. is a multinational corporation vendor of computers, computer components, computer software, and information technology services, founded on February 24, 1982....
     launches a 64-bit SPARC
    SPARC

    SPARC is a Reduced Instruction Set Computer microprocessor instruction set Computer architecture originally designed in 1985 by Sun Microsystems....
     processor, the UltraSPARC. Fujitsu
    Fujitsu

    is a Japanese company specializing in semiconductors, air conditioners, computers , telecommunications, and Service , and is headquartered in Minato, Tokyo, Tokyo....
    -owned HAL Computer Systems
    HAL Computer Systems

    HAL Computer Systems, Inc was a Campbell, California-based computer manufacturer. It was founded in 1990 by Andrew Heller, a principal designer of the original IBM POWER architecture....
     launches workstations based on a 64-bit CPU, HAL's independently designed first-generation SPARC64. IBM releases the A10 and A30 microprocessors, 64-bit PowerPC AS processors. IBM also releases a 64-bit AS/400 system upgrade, which can convert the operating system, database and applications. DEC releases OpenVMS
    OpenVMS

    OpenVMS , previously known as VAX-11/VMS, VAX/VMS or VMS, is the name of a high-end computer server operating system that runs on the VAX and DEC Alpha families of computers, developed by Digital Equipment Corporation of Maynard, Massachusetts, Massachusetts , and most recently on Hewlett-Packard systems built around the In...
     7.0, the first full 64-bit version of OpenVMS for Alpha.


  • 1996: Nintendo
    Nintendo

    is a global company located in Kyoto, Japan founded on September 23, 1889 by Fusajiro Yamauchi to produce handmade hanafuda cards. By 1963, the company had tried several small niche businesses, such as a cab company and a love hotel....
     introduces the Nintendo 64
    Nintendo 64

    The , often abbreviated as N64, is Nintendo's third home video game console for the international market. Named for its 64-bit CPU, it was released on June 23, 1996 in Japan, September 29, 1996 in North America, March 1, 1997 in Europe and Australia, September 1, 1997 in France and December 10, 1997 in Brazil....
     video game console, built around a low-cost variant of the MIPS R4000. HP releases an implementation of the 64-bit 2.0 version of their PA-RISC processor architecture, the PA-8000.


  • 1997: IBM releases the RS64 line of 64-bit PowerPC
    PowerPC

    PowerPC is a RISC instruction set architecture created by the 1991 Apple Inc.?IBM?Motorola alliance, known as AIM alliance. Originally intended for personal computers, PowerPC CPUs have since become popular embedded system and high-performance processors....
    /PowerPC AS processors.


  • 1998: IBM releases the POWER3
    POWER3

    The POWER3 chip is a CPU, designed and exclusively manufactured by IBM, that implements the 32/64-bit PowerPC instruction set architecture, including all of the optional instructions of the ISA such as the POWER2....
     line of full-64-bit PowerPC/POWER
    IBM POWER

    POWER is a RISC instruction set architecture designed by International Business Machines. The name is a backronym for Performance Optimization With Enhanced RISC....
     processors. Sun releases Solaris 7, with full 64-bit UltraSPARC support.


  • 1999: Intel releases the instruction set
    Instruction set

    An instruction set is a list of all the instruction , and all their variations, that a processor can execute.Instructions include:* Arithmetic such as add and subtract...
     for the IA-64 architecture. AMD publicly discloses its set of 64-bit extensions to IA-32, called x86-64
    X86-64

    x86-64 is a superset of the x86. x86-64 Central processing units can run existing 32-bit or 16-bit x86 programs at full speed, but also support new programs written with a 64-bit address space and other additional capabilities....
     (later renamed AMD64).


  • 2000: IBM ships its first 64-bit ESA/390
    ESA/390

    ESA/390 was introduced in September 1990 and is IBM's last 31-bit-address/32-bit-data IBM mainframe computing design, copied by Amdahl, Hitachi, Ltd., and Fujitsu among other competitors....
    -compatible mainframe
    Mainframe computer

    Mainframes are computers used mainly by large organizations for critical applications, typically bulk data processing such as census, industry and consumer statistics, Enterprise Resource Planning, and financial transaction processing....
    , the zSeries
    ZSeries

    IBM System z, or earlier IBM eServer zSeries, is a brand name designated by IBM to all its mainframe computers.In 2000, IBM rebranded the existing System/390 to IBM eServer zSeries with the e depicted in IBM's red trademarked symbol....
     z900, and its new z/OS
    Z/OS

    z/OS is a 64-bit operating system for mainframe computers, created by IBM. It is the successor to OS/390, which in turn followed MVS and combined a number of formerly separate, related products....
     operating system. 64-bit Linux on zSeries
    Linux on zSeries

    Linux on System z is the collective term for the Linux operating system compiled to run on IBM mainframes, especially System z machines. Other terms with the same meaning include Linux on System z10, Linux on System z9, Linux on zSeries, Linux/390, zLinux, z/Linux, etc....
     follows almost immediately.


  • 2001: Intel finally ships its 64-bit processor line, now branded Itanium
    Itanium

    Itanium is the brand name for 64-bit Intel microprocessors that implement the Intel Itanium architecture . Intel has released two processor families using the brand: the original Itanium and the Itanium 2....
    , targeting high-end servers. It fails to meet expectations due to the repeated delays in getting IA-64 to market. Linux
    Linux

    Linux is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed by anyone under the terms of the GNU GPL license...
     is the first operating system to run on the processor at its release.


  • 2003: AMD introduces its Opteron
    Opteron

    The Opteron is Advanced Micro Devices's x86 server Central processing unit line, and was the first processor to implement the AMD64 instruction set architecture ....
     and Athlon 64
    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....
     processor lines, based on its AMD64 architecture which is the first x86 based 64 bit processor architecture. Apple
    Apple Computer

    Apple Inc., formerly Apple Computer Inc., is an United States multinational corporation which designs and manufactures consumer electronics and software products....
     also ships the 64-bit "G5" PowerPC 970 CPU courtesy of IBM, along with an update to its Mac OS X
    Mac OS X

    Mac OS X is a line of computer operating systems developed, marketed, and sold by Apple Inc., and since 2002 has been included with all new Macintosh computer systems....
     operating system which adds partial support for 64-bit mode. Several Linux
    Linux

    Linux is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed by anyone under the terms of the GNU GPL license...
     distributions
    Linux distribution

    A Linux distribution is a member of the family of Unix-like software distributions built on top of the Linux kernel. Such distributions consist of a large collection of software applications such as word processors, spreadsheets, media players and database applications....
     release with support for AMD64. Microsoft
    Microsoft

    Microsoft Corporation is a multinational corporation computer technology corporation that develops, manufactures, licenses, and supports a wide range of computer software products for computing devices....
     announces plans to create a version of its Windows
    Microsoft Windows

    Microsoft Windows is a series of software operating systems and graphical user interfaces produced by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces ....
     operating system to support the AMD64 architecture. FreeBSD
    FreeBSD

    FreeBSD is a Unix-like free software operating system descended from AT&T Unix via the Berkeley Software Distribution branch through the 386BSD and Berkeley Software Distribution#4.4BSD and descendants operating systems....
     releases with support for AMD64. Intel maintains that its Itanium chips would remain its only 64-bit processors.


  • 2004: Intel, reacting to the market success of AMD, admits it has been developing a clone of the AMD64 extensions named IA-32e (later renamed EM64T). Intel also ships updated versions of its Xeon
    Xeon

    The Xeon brand refers to many families of Intel Corporation's x86 architecture multiprocessing Central processing units ? for dual processor and multi-processor configuration on a single motherboard targeted at non-consumer markets of server and workstation computers, and also at blade servers and embedded systems....
     and Pentium 4
    Pentium 4

    The Pentium 4 brand refers to Intel's line of single-core mainstream Desktop computer and laptop central processing units introduced on November 20, 2000 ....
     processor families supporting the new instructions.


  • 2004: VIA Technologies
    VIA Technologies

    VIA Technologies is a Taiwanese manufacturer of integrated circuits, mainly motherboard chipsets, Central processing unit, and computer memory, and is part of the Formosa Plastics Group....
     announces the Isaiah 64-bit processor.


  • 2005: On January 31, Sun releases Solaris 10 with support for AMD64 and EM64T processors. On April 30, Microsoft releases Windows XP Professional x64 Edition for AMD64 and EM64T processors.


  • 2006: Sony, IBM, and Toshiba begin manufacturing of the 64-bit Cell processor for use in the PlayStation 3
    PlayStation 3

    The PlayStation 3 is the third home video game console produced by Sony Computer Entertainment, and the successor to the PlayStation 2 as part of the PlayStation ....
    , servers, workstations, and other appliances.


32 vs 64 bit

A change from a 32-bit
32-bit

The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295 or -2,147,483,648 through 2,147,483,647 using two's complement encoding....
 to a 64-bit architecture is a fundamental alteration, as most operating system
Operating system

An operating system is an interface between hardware and applications; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer....
s must be extensively modified to take advantage of the new architecture. Other software must also be ported
Porting

In computer science, porting is the process of adapting software so that an executable Computer program can be created for a computing environment that is different from the one for which it was originally designed ....
 to use the new capabilities; older software is usually supported through either a hardware compatibility mode (in which the new processors support the older 32-bit version of the instruction set as well as the 64-bit version), through software emulation, or by the actual implementation of a 32-bit processor core within the 64-bit processor (as with the Itanium processors from Intel, which include an x86 processor core to run 32-bit x86 applications). The operating systems for those 64-bit architectures generally support both 32-bit and 64-bit applications.

One significant exception to this is the AS/400, whose software runs on a virtual ISA, called TIMI (Technology Independent Machine Interface) which is translated to native machine code by low-level software before being executed. The low-level software is all that has to be rewritten to move the entire OS and all software to a new platform, such as when IBM transitioned their line from the older 32/48-bit "IMPI" instruction set to 64-bit PowerPC (IMPI wasn't anything like 32-bit PowerPC, so this was an even bigger transition than from a 32-bit version of an instruction set to a 64-bit version of the same instruction set).

Also, 64-bit processors calculate particular tasks (such as factorials of large figures) twice as fast as working in 32-bit environments (given example is derived from comparison between 32-bit and 64-bit Windows Calculator; noticeable for factorial of say 100,000).

While 64-bit architectures indisputably make working with large data sets in applications such as digital video
Digital video

Digital video is a type of video recording system that works by using a digital rather than an analog signal video signal.The terms camera, video camera, and camcorder are used interchangeably in this article....
, scientific computing, and large database
Database

A database is a structured collection of records or data that is stored in a computer system. The structure is achieved by organizing the data according to a database model....
s easier, there has been considerable debate as to whether they or their 32-bit compatibility modes will be faster than comparably-priced 32-bit systems for other tasks. In x86-64
X86-64

x86-64 is a superset of the x86. x86-64 Central processing units can run existing 32-bit or 16-bit x86 programs at full speed, but also support new programs written with a 64-bit address space and other additional capabilities....
 architecture (AMD64), the majority of the 32-bit operating systems and applications are able to run smoothly on the 64-bit hardware.

Sun's 64-bit Java virtual machines are slower to start up than their 32-bit virtual machines because Sun has only implemented the "server" JIT
Just-in-time compilation

In computing, just-in-time compilation , also known as dynamic translation, is a technique for improving the runtime performance of a computer program....
 compiler (C2) for 64-bit platforms. The "client" JIT compiler (C1), which produces less efficient code but compiles much faster, is unavailable on 64-bit platforms.

It should be noted that speed is not the only factor to consider in a comparison of 32-bit and 64-bit processors. Applications such as multi-tasking, stress testing, and clustering—for HPC (high-performance computing
High-performance computing

High-performance computing uses supercomputers and computer clusters to solve advanced computation problems. Today, computer systems approaching the teraflops-region are counted as HPC-computers....
)—may be more suited to a 64-bit architecture given the correct deployment. 64-bit clusters have been widely deployed in large organizations such as IBM, HP and Microsoft, for this reason.

Pros and cons

A common misconception is that 64-bit architectures are no better than 32-bit architectures unless the computer has more than 4 GB of memory. This is not entirely true:

  • Some operating systems reserve portions of process
    Process (computing)

    In computing, a process is an Object of a computer program that is being sequentially executed by a computer system that has the ability to run several computer programs Concurrency ....
     address space
    Address space

    In computing, an address space defines a range of discrete addresses, each of which may correspond to a physical or virtual memory register, a Node , peripheral device, disk sector or other logical or physical entity....
     for OS use, effectively reducing the total address space available for mapping memory for user programs. For instance, Windows XP DLLs and userland OS components are mapped into each process's address space, leaving only 2 to 3.8 GB (depending on the settings) address space available, even if the computer has 4 GB of RAM. This restriction is not present in 64-bit operating systems. (This also applies to computers running Windows Vista with Service Pack 1 as it only shows the installed RAM not the usable.)


  • Memory-mapped file
    Memory-mapped file

    A 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....
    s are becoming more difficult to implement in 32-bit architectures, especially due to the introduction of relatively cheap recordable DVD technology. A 4 GB file is no longer uncommon, and such large files cannot be memory mapped easily to 32-bit architectures; only a region of the file can be mapped into the address space, and to access such a file by memory mapping, those regions will have to be mapped into and out of the address space as needed. This is a problem, as memory mapping remains one of the most efficient disk-to-memory methods, when properly implemented by the OS.
  • Some programs such as data encryption software can benefit greatly from 64-bit registers (if the software is 64-bit compiled) and effectively execute 3 to 5 times faster on 64-bit than on 32-bit.


  • Some complex numerical analysis
    Numerical analysis

    Numerical analysis is the study of algorithms for the problems of continuous mathematics .One of the earliest mathematical writings is the Babylonian tablet YBC 7289, which gives a sexagesimal numerical approximation of , the length of the diagonal in a unit square....
     algorithms are limited in their precision by the errors that can creep in because not all floating point numbers can be accurately represented with a small number of bits. Creeping inaccuracies can lead to incorrect results, often leading to attempts to divide by zero, or to not identify two quantities as being identical for practical purposes. International Computers Limited added 128-bit support to the ICL 2900 Series
    ICL 2900 Series

    The ICL 2900 Series was a range of mainframe computer computer systems announced by the UK manufacturer International Computers Limited on 9 October 1974....
     in 1974 largely as a result of requests from the scientific community.


The main disadvantage of 64-bit architectures is that relative to 32-bit architectures the same data occupies more space in memory (due to swollen pointers and possibly other types and alignment padding). This increases the memory requirements of a given process and can have implications for efficient processor cache utilization. Maintaining a partial 32-bit model is one way to handle this and is in general reasonably effective. In fact, the highly performance-oriented z/OS
Z/OS

z/OS is a 64-bit operating system for mainframe computers, created by IBM. It is the successor to OS/390, which in turn followed MVS and combined a number of formerly separate, related products....
 operating system takes this approach currently, requiring program code to reside in any number of 32-bit
32-bit

The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295 or -2,147,483,648 through 2,147,483,647 using two's complement encoding....
 address spaces while data objects can (optionally) reside in 64-bit regions.

Currently, most commercial x86 software is compiled into 32-bit code, not 64-bit code, so it does not take advantage of the larger 64-bit address space or wider 64-bit registers and data paths on x86 processors, or the additional registers in 64-bit mode. However, users of most RISC platforms, and users of free
Free software

Free Software or software libre is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with minimal restrictions only to ensure that further recipients can also do these things and to prevent consumer-facing hardware...
 or open source
Open source

Open source is an approach to design, development, and distribution offering practical accessibility to a product's source . Some consider open source as one of various possible design approaches, while others consider it a critical Strategy element of their business operations....
 operating systems (where the source code
Source code

In computer science, source code is any collection of statements or declarations written in some human-readable computer programming language....
 is available for recompiling with a 64-bit compiler) have been able to use exclusive 64-bit computing environments for years. Not all such applications require a large address space nor manipulate 64-bit data items, so they wouldn't benefit from the larger address space or wider registers and data paths. The main advantage to 64-bit versions of such applications is the ability to access more registers in the x86-64
X86-64

x86-64 is a superset of the x86. x86-64 Central processing units can run existing 32-bit or 16-bit x86 programs at full speed, but also support new programs written with a 64-bit address space and other additional capabilities....
 architecture.

Software availability

x86-based 64-bit systems sometimes lack equivalents to software that is written for 32-bit architectures. The most severe problem in Microsoft Windows is incompatible device driver
Device driver

In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
s. Although most software can run in a 32-bit compatibility mode (also known as an emulation mode, e.g. Microsoft WoW64
WOW64

WoW64 is a subsystem of the Microsoft Windows operating system that is capable of running 32-bit applications and is included on all 64-bit versions of Windows ? including Windows 2000, Windows XP Professional x64 Edition, IA-64 and x86-64 versions of Windows Server 2003, 64-bit versions of Windows Vista and Windows Server 2008, as well as 6...
 Technology for IA64) or run in 32-bit mode natively (on AMD64), it is usually impossible to run a driver (or similar software) in that mode since such a program
Computer program

Computer programs are Instruction for a computer. A computer requires programs to function. Moreover, a computer program does not run unless its instructions are executed by a Central processing unit; however, a program may communicate an Algorithm#Formalization of algorithms to people without running....
 usually runs in between the OS
Operating system

An operating system is an interface between hardware and applications; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer....
 and the hardware, where direct emulation cannot be employed. Currently the 64-bit versions for many existing device drivers are not available, so using 64-bit Microsoft Windows operating system can become frustrating as a result. However most devices made after February 2007 have 64-bit drivers available as well as many devices made in the later 2006 period.

Because device drivers in operating systems with monolithic kernels, and in many operating systems with hybrid kernel
Hybrid kernel

A hybrid kernel is a Kernel architecture based on combining aspects of microkernel and monolithic kernel architectures used in computer operating systems....
s, execute within the operating system kernel, it is possible to run the kernel as a 32-bit process while still supporting 64-bit user processes. This provides the memory and performance benefits of 64-bit for users without breaking binary compatibility with existing 32-bit device drivers, at the cost of some additional overhead within the kernel. This is the mechanism by which Mac OS X
Mac OS X

Mac OS X is a line of computer operating systems developed, marketed, and sold by Apple Inc., and since 2002 has been included with all new Macintosh computer systems....
 enables 64-bit processes while still supporting 32-bit device drivers.

64-bit data models

Converting application software written in a high-level language from a 32-bit architecture to a 64-bit architecture varies in difficulty. One common recurring problem is that some programmers assume that pointers have the same length as some other data type. These programmers assume they can transfer quantities between these data types without losing information. Those assumptions happen to be true on some 32-bit machines (and even some 16-bit machines), but they are no longer true on 64-bit machines. The C programming language
C (programming language)

C is a general-purpose computer programming language originally developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories to implement the Unix operating system....
 and its descendant C++
C++

C++ is a general-purpose programming language. It is regarded as a middle-level language, as it comprises a combination of both high-level programming language and low-level programming language language features....
 make it particularly easy to make this sort of mistake. Differences between the C89
C (programming language)

C is a general-purpose computer programming language originally developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories to implement the Unix operating system....
 and C99
C (programming language)

C is a general-purpose computer programming language originally developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories to implement the Unix operating system....
 language standards also exacerbate the problem

To avoid this mistake in C and C++, the sizeof operator can be used to determine the size of these primitive types if decisions based on their size need to be made, both at compile- and run-time. Also, the <limits.h
Limits.h

limits.h is the header of the general purpose standard library of the C programming language which includes definitions of the characteristics of common variable types....
> header in the C99
C (programming language)

C is a general-purpose computer programming language originally developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories to implement the Unix operating system....
 standard, and numeric_limits class in <limits> header in the C++ standard, give more helpful info; sizeof only returns the size in chars
Character (computing)

In computer and machine-based telecommunications terminology, a character is a unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written language form of a natural language....
. This used to be misleading, because the standards leave the definition of the CHAR_BIT macro, and therefore the number of bits in a char, to the implementations. However, except for those compilers targeting DSP
Digital signal processor

A digital signal processor is a specialized microprocessor designed specifically for digital signal processing, generally in real-time computing....
s, "64 bits

8 chars of 8 bits each" has become the norm.

One needs to be careful to use the ptrdiff_t type (in the standard header <stddef.h>) for the result of subtracting two pointers; too much code incorrectly uses "int" or "long" instead. To represent a pointer (rather than a pointer difference) as an integer, use uintptr_t where available (it is only defined in C99, but some compilers otherwise conforming to an earlier version of the standard offer it as an extension).

Neither C nor C++ define the length of a pointer, int, or long to be a specific number of bits. C99, however, stdint.h
Stdint.h

stdint.h is a header file in the C standard library introduced in the C99 standard library section 7.18 to allow programmers to write more portable code by providing a set of typedefs that specify exact-width integer types, together with the defined minimum and maximum allowable values for each type, using macros....
 provides names for integer types with certain numbers of bits where those types are available.

In most programming environments on 32-bit machines, pointers, "int" types, and "long" types are all 32 bits wide.

However, in many programming environments on 64-bit machines, "int" variables are still 32 bits wide, but "long"s and pointers are 64 bits wide. These are described as having an LP64 data model
Data model

A data model in software engineering is an abstract model that describes how Data is represented and accessed. Data models formally define data elements and relationships among data elements for a domain of interest....
. Another alternative is the ILP64 data model in which all three data types are 64 bits wide, and even SILP64 where "short" variables are also 64 bits wide. However, in most cases the modifications required are relatively minor and straightforward, and many well-written programs can simply be recompiled for the new environment without changes. Another alternative is the LLP64 model, which maintains compatibility with 32-bit code by leaving both int and long as 32-bit. "LL" refers to the "long long" type, which is at least 64 bits on all platforms, including 32-bit environments.

Many 64-bit compilers today use the LP64 model (including Solaris, AIX, HP, Linux, Mac OS X, FreeBSD, and IBM z/OS native compilers). Microsoft's VC++ compiler uses the LLP64 model. The disadvantage of the LP64 model is that storing a long into an int may overflow. On the other hand, casting a pointer to a long will work. In the LLP model, the reverse is true. These are not problems which affect fully standard-compliant code but code is often written with implicit assumptions about the widths of integer types.

Note that a programming model is a choice made on a per-compiler basis, and several can coexist on the same OS. However typically the programming model chosen by the OS API as primary model dominates.

Another consideration is the data model used for driver
Device driver

In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
s. Drivers make up the majority of the operating system code in most modern operating systems (although many may not be loaded when the operating system is running). Many drivers use pointers heavily to manipulate data, and in some cases have to load pointers of a certain size into the hardware they support for DMA
Direct memory access

Direct memory access is a feature of modern computers and microprocessors that allows certain hardware subsystems within the computer to access system Computer storage for reading and/or writing independently of the central processing unit....
. As an example, a driver for a 32-bit PCI device asking the device to DMA data into upper areas of a 64-bit machine's memory could not satisfy requests from the operating system to load data from the device to memory above the 4 gigabyte barrier, because the pointers for those addresses would not fit into the DMA registers of the device. This problem is solved by having the OS take the memory restrictions of the device into account when generating requests to drivers for DMA, or by using an IOMMU
IOMMU

In computing, an input/output memory management unit is a memory management unit that connects a direct memory access-capable I/O computer bus to the main memory....
.

64-bit data models
Data model short int long long long pointers
LLP64 16 32 32 64 64
LP64 16 32 64 64 64
ILP64 16 64 64 64 64
SILP64 64 64 64 64 64


Current 64-bit microprocessor architectures

64-bit microprocessor architectures include:
  • 64-bit extensions of the Intel x86 architecture, commonly known generically as "x86-64
    X86-64

    x86-64 is a superset of the x86. x86-64 Central processing units can run existing 32-bit or 16-bit x86 programs at full speed, but also support new programs written with a 64-bit address space and other additional capabilities....
    " or "x64":
    • AMD
      Advanced Micro Devices

      Advanced Micro Devices, Inc. is an United States multinational corporation semiconductor industry company based in Sunnyvale, California, that develops Central processing unit and related technologies for commercial and consumer markets....
      's AMD64 extensions (used in Athlon 64
      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....
      , Opteron
      Opteron

      The Opteron is Advanced Micro Devices's x86 server Central processing unit line, and was the first processor to implement the AMD64 instruction set architecture ....
      , Sempron
      Sempron

      Sempron has been the marketing name used by AMD for several different entry level desktop CPUs, using several different technologies and CPU socket formats....
      , Turion 64
      Turion 64

      Turion 64 is the brand name AMD applies to its 64-bit low-consumption Central Processing Unit codenamed K8L. The Turion 64 and Turion 64 X2 processors compete with Intel's mobile processors, initially the Pentium M and currently the Intel Core and Intel Core 2 processors....
       and Phenom
      Phenom (processor)

      Phenom is the Advanced Micro Devices desktop processor line based on the AMD K10 microarchitecture, or Family 10h Processors, as AMD calls them....
       processors)
    • Intel's Intel 64 extensions (used in newer Celeron
      Celeron

      The Celeron brand is a range of x86 CPUs from Intel targeted at budget/value personal computers?with the motto, "delivering great quality at an exceptional value"....
      , Pentium 4
      Pentium 4

      The Pentium 4 brand refers to Intel's line of single-core mainstream Desktop computer and laptop central processing units introduced on November 20, 2000 ....
      , Pentium D
      Pentium D

      The Pentium D brand refers to two series of desktop dual-core 64-bit x86 CPU with the NetBurst microarchitecture manufactured by Intel Corporation....
      , Xeon
      Xeon

      The Xeon brand refers to many families of Intel Corporation's x86 architecture multiprocessing Central processing units ? for dual processor and multi-processor configuration on a single motherboard targeted at non-consumer markets of server and workstation computers, and also at blade servers and embedded systems....
      , Core 2, Core i7
      Intel Core i7

      Intel Core i7 is a family of three Intel desktop x86-64 processors, the first processors released using the Intel Nehalem and the successor to the Intel Core 2 family....
      , and Atom
      Intel Atom

      Intel Atom is the brand name for a line of x86 and x86-64 CPUs from Intel, previously List of Intel codenames Silverthorne and Diamondville processors, designed for a 45 nm CMOS process and intended for use in MIDs, smart phones and ultra-mobile PCs meant for portable and low-power applications....
       processors)
    • VIA's 64-bit extensions, used in the VIA Nano
      VIA Nano

      The VIA Nano is a 64-bit central processing unit for personal computers released by VIA Technologies in 2008 after five years of developmentby its CPU division, Centaur Technology....
       processors
  • Power Architecture
    Power Architecture

    Power Architecture is a broad term to describe similar RISC instruction sets for microprocessors developed and manufactured by such companies as IBM, Freescale, Applied Micro Circuits Corporation, Tundra Semiconductor and P.A....
    :
    • IBM's POWER6
      POWER6

      The POWER6 microprocessor is IBM's follow-on to the POWER5. It is part of the eCLipz, said to have a goal of converging IBM's server hardware where practical ....
       processor
    • IBM's PowerPC 970
      PowerPC 970

      The PowerPC 970, PowerPC 970FX, PowerPC 970GX, and PowerPC 970MP, are 64-bit Power Architecture central processing unit from IBM introduced in 2002....
       processor
    • The Cell Broadband Engine used in the PlayStation 3
      PlayStation 3

      The PlayStation 3 is the third home video game console produced by Sony Computer Entertainment, and the successor to the PlayStation 2 as part of the PlayStation ....
      , designed by IBM, Toshiba
      Toshiba

      is a multinational corporation list of conglomerates manufacturing company, headquartered in Tokyo, Japan. The company's main business is in Infrastructure, Consumer Products, and Electronic devices and components....
       and Sony
      Sony

      is a multinational corporation list of conglomerates corporation headquartered in Minato, Tokyo, Japan, and one of the world's largest media conglomerates with revenue exceeding US$99.1 billion ....
      , combines a 64-bit Power architecture processor with eight 128-bit "Synergistic Processing Elements"
    • IBM's "Xenon
      Xenon (processor)

      Xenon is a Central processing unit that is used in the Xbox 360 game console. The processor, internally codenamed "Waternoose" by IBM and "XCPU" by Microsoft, is based on IBM PowerPC instruction set architecture, consisting of three independent Multi-core on a single die....
      " processor used in the Microsoft
      Microsoft

      Microsoft Corporation is a multinational corporation computer technology corporation that develops, manufactures, licenses, and supports a wide range of computer software products for computing devices....
       Xbox 360
      Xbox 360

      The Xbox 360 is the second video game console produced by Microsoft, and the successor to the Xbox. The Xbox 360 competes with Sony's PlayStation 3 and Nintendo's Wii as part of the History of video game consoles of video game consoles....
       comprises three 64-bit PowerPC cores.
  • SPARC
    SPARC

    SPARC is a Reduced Instruction Set Computer microprocessor instruction set Computer architecture originally designed in 1985 by Sun Microsystems....
     V9 architecture:
    • Sun's UltraSPARC processors
    • Fujitsu's SPARC64 processors
  • IBM's z/Architecture
    Z/Architecture

    z/Architecture, initially and briefly called ESA/390 Modal Extensions , refers to IBM's 64-bit computing architecture for the current generation of IBM mainframe computers....
    , used by IBM zSeries and System z9
    System z9

    IBM System z9 is a line of IBM Mainframe computer. It was announced on July 25, 2005 and the first models were available on September 16, 2005....
     mainframes, a 64-bit version of the ESA/390
    ESA/390

    ESA/390 was introduced in September 1990 and is IBM's last 31-bit-address/32-bit-data IBM mainframe computing design, copied by Amdahl, Hitachi, Ltd., and Fujitsu among other competitors....
     architecture
  • Intel's IA-64 architecture (used in Itanium
    Itanium

    Itanium is the brand name for 64-bit Intel microprocessors that implement the Intel Itanium architecture . Intel has released two processor families using the brand: the original Itanium and the Itanium 2....
     processors)
  • MIPS Technologies' MIPS64 architecture
    MIPS architecture

    MIPS is a RISC instruction set architecture developed by MIPS Technologies . In the mid to late 1990s, it was estimated that one in three RISC microprocessors produced were MIPS implementations....


Most 64-bit processor architectures can execute code for the 32-bit version of the architecture natively without any performance penalty. This kind of support is commonly called bi-arch support or more generally multi-arch support.

Images

In digital imaging, 64-bit refers to 48-bit images
48-bit

Computers with 48-bit Word include CDC 1604 and BESM#BESM-6.The IBM AS/400, in its Complex instruction set computer variants, is a 48-bit addressing system....
 with a 16-bit
16-bit

16-bit architectureThe HP 2100#Descendants and variants , introduced in 1975, was the world's first 16-bit microprocessor.Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816....
 alpha channel.

See also

  • Computer memory
    Computer memory

    Computer memory is usually meant to refer to the semiconductor technology that is used to store information in Electronics devices. Current primary computer memory makes use of integrated circuits consisting of silicon-based transistors....


External links