Am386
Encyclopedia
The Am386 CPU
was a 100%-compatible clone
of the Intel 80386
design released by AMD in 1991. It sold millions of units, positioning AMD
as a legitimate competitor to Intel
, rather than being merely a second source for x86 CPUs (then termed 8086-family
).
, Intel 80186
and Intel 80286
designs, and AMD's interpretation of the contract, made up in 1982, was that it covered all derivatives of them. Intel, however, claimed that the contract only covered the 80286 and prior processors and forbade AMD the right to manufacture 80386 CPUs in 1987. After a few years in the courtrooms, AMD finally won the case and the right to sell their Am386 in 1992. This also paved the way for competition in the 80386
-compatible 32-bit
CPU market and so lowered the cost of owning a PC.
While Intel's 386 design peaked at 33 MHz
, AMD released a 40 MHz version of both its 386DX and 386SX, extending the lifespan of the architecture. The AMD 386DX-40 was popular with small manufacturers of PC clones and with budget-minded computer enthusiasts because it offered near-80486 performance at a much lower price than a real 486.
The 386DX-40 could match or even slightly outperform a 486SX
-25 in popular benchmark
s and many real-world applications, while costing less. Integer performance at 40 MHz thus approached that of low-end 486 CPUs, but rarely exceeded it. This is because the 486 needed fewer clock cycles per instruction, thanks to its tighter pipelining (more overlapping of internal processing) in combination with a crucial on-chip CPU cache
. However, because the Am386DX-40 had the same 32-bit
width on its data bus as an 80486, but operating at the same 40 MHz rate as the processor, (rather than the 25 to 33 MHz buses of the 486 DX-2s) it had comparatively good memory and I/O performance.
performance of the Am386 could be boosted with the addition of a 80387DX or 80387SX coprocessor
, although performance would still not approach that of the on-chip FPU
of the 486DX. This made the Am386DX a suboptimal choice for scientific applications and CAD
using floating point intensive calculations. However, both were niche markets in the early 1990s and the chip sold well, first as a mid-range contender, and then as a budget chip. Although motherboard
s using the older 386 CPUs often had limited memory expansion possibilities and therefore struggled under Windows 95
's memory requirements, boards using the Am386 were sold well into the mid-1990s; at the end as budget motherboards for those who were only interested in running MS-DOS
or Windows 3.1x
applications.
The Am386 and its low-power successors were also popular choices for embedded system
s, for a much longer period than their life span as PC
processors.
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
was a 100%-compatible clone
IBM PC compatible
IBM PC compatible computers are those generally similar to the original IBM PC, XT, and AT. Such computers used to be referred to as PC clones, or IBM clones since they almost exactly duplicated all the significant features of the PC architecture, facilitated by various manufacturers' ability to...
of the Intel 80386
Intel 80386
The Intel 80386, also known as the i386, or just 386, was a 32-bit microprocessor introduced by Intel in 1985. The first versions had 275,000 transistors and were used as the central processing unit of many workstations and high-end personal computers of the time...
design released by AMD in 1991. It sold millions of units, positioning AMD
Advanced Micro Devices
Advanced 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...
as a legitimate competitor to Intel
Intel Corporation
Intel 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...
, rather than being merely a second source for x86 CPUs (then termed 8086-family
Intel 8086
The 8086 is a 16-bit microprocessor chip designed by Intel between early 1976 and mid-1978, when it was released. The 8086 gave rise to the x86 architecture of Intel's future processors...
).
History and design
While the AM386 CPU was essentially ready to be released prior to 1991, Intel kept it tied up in court. AMD had previously been a second-source manufacturer of Intel's Intel 8086Intel 8086
The 8086 is a 16-bit microprocessor chip designed by Intel between early 1976 and mid-1978, when it was released. The 8086 gave rise to the x86 architecture of Intel's future processors...
, Intel 80186
Intel 80186
The 80188 is a version with an 8-bit external data bus, instead of 16-bit. This makes it less expensive to connect to peripherals. The 80188 is otherwise very similar to the 80186. It has a throughput of 1 million instructions per second....
and Intel 80286
Intel 80286
The Intel 80286 , introduced on 1 February 1982, was a 16-bit x86 microprocessor with 134,000 transistors. Like its contemporary simpler cousin, the 80186, it could correctly execute most software written for the earlier Intel 8086 and 8088...
designs, and AMD's interpretation of the contract, made up in 1982, was that it covered all derivatives of them. Intel, however, claimed that the contract only covered the 80286 and prior processors and forbade AMD the right to manufacture 80386 CPUs in 1987. After a few years in the courtrooms, AMD finally won the case and the right to sell their Am386 in 1992. This also paved the way for competition in the 80386
Intel 80386
The Intel 80386, also known as the i386, or just 386, was a 32-bit microprocessor introduced by Intel in 1985. The first versions had 275,000 transistors and were used as the central processing unit of many workstations and high-end personal computers of the time...
-compatible 32-bit
32-bit
The 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....
CPU market and so lowered the cost of owning a PC.
While Intel's 386 design peaked at 33 MHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, AMD released a 40 MHz version of both its 386DX and 386SX, extending the lifespan of the architecture. The AMD 386DX-40 was popular with small manufacturers of PC clones and with budget-minded computer enthusiasts because it offered near-80486 performance at a much lower price than a real 486.
The 386DX-40 could match or even slightly outperform a 486SX
Intel 80486SX
The Intel's i486SX was a modified Intel 486DX microprocessor with its floating-point unit disconnected. All early 486SX chips were actually i486DX chips with a defective FPU...
-25 in popular benchmark
Benchmark (computing)
In computing, a benchmark is the act of running a computer program, a set of programs, or other operations, in order to assess the relative performance of an object, normally by running a number of standard tests and trials against it...
s and many real-world applications, while costing less. Integer performance at 40 MHz thus approached that of low-end 486 CPUs, but rarely exceeded it. This is because the 486 needed fewer clock cycles per instruction, thanks to its tighter pipelining (more overlapping of internal processing) in combination with a crucial on-chip CPU cache
CPU cache
A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations...
. However, because the Am386DX-40 had the same 32-bit
32-bit
The 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....
width on its data bus as an 80486, but operating at the same 40 MHz rate as the processor, (rather than the 25 to 33 MHz buses of the 486 DX-2s) it had comparatively good memory and I/O performance.
Am386DX data
- 32-bit data bus, can select between either a 32-bit bus or a 16-bit bus by use of the BS16 input
- 32-bit physical address space, 4 Gbyte physical memory address space
- fetches code in four-byte units
The various models of the Am386DX, data from Model number Frequency FSB Voltage CPU core voltageThe CPU core voltage is the power supply voltage supplied to the CPU , GPU, or other device containing a processing core...
Power CPU power dissipationCentral processing unit power dissipation or CPU power dissipation is the process in which central processing units consume electrical energy, and dissipate this energy both by the action of the switching devices contained in the CPU and by the energy lost in the form of heat due to the impedance...
Socket CPU socketA CPU socket or CPU slot is a mechanical component that provides mechanical and electrical connections between a microprocessor and a printed circuit board . This allows the CPU to be replaced without soldering....
Release date AMD Am386DX/DXL-20 20 MHz 20 MHz 5 V 1.05 Watt 132-pin CPGA 1991 AMD Am386DX/DXL-25 25 MHz 25 MHz 5 V 1.31 Watt 132-pin CPGA March 1991 AMD Am386DX/DXL-33 33 MHz 33 MHz 5 V 1.73 Watt 132-pin CPGA 1991 AMD Am386DX/DXL-40 40 MHz 40 MHz 5 V 2.10 Watt 132-pin CPGA 1992 AMD Am386DX-40 40 MHz 40 MHz 5 V 3.03 Watt 132-pin PQFP 1992
AM386 SX
In 1991 AMD also introduced advanced versions of the 386SX processor -again not as a second source production of the Intel chip, but as a reverse engineered pin compatible version. In fact, it was AMD's first entry in the x86 market other than as a second source for Intel. AMD 386SX processors were available at faster clock speeds at the time they were introduced and still cheaper than the Intel 386SX. Produced in 0.8 µm technology and using a static core, their clock speed could be dropped down to 0 MHz, consuming just some mWatts. Power consumption was up to 35% lower than with Intel's design and even lower than the 386SL's, making the AMD 386SX the ideal chip for both desktop and mobile computers. The SXL versions featured advanced power management functions and used even less power.Am386SX data
- 16-bit data bus, no bus sizing option
- 24-bit physical address space, 16 Mbyte physical memory address space
- prefetch unit reads two bytes as one unit (like the 80286).
The various models of the Am386DX, data from Model number Frequency FSB Voltage CPU core voltageThe CPU core voltage is the power supply voltage supplied to the CPU , GPU, or other device containing a processing core...
Power CPU power dissipationCentral processing unit power dissipation or CPU power dissipation is the process in which central processing units consume electrical energy, and dissipate this energy both by the action of the switching devices contained in the CPU and by the energy lost in the form of heat due to the impedance...
Socket CPU socketA CPU socket or CPU slot is a mechanical component that provides mechanical and electrical connections between a microprocessor and a printed circuit board . This allows the CPU to be replaced without soldering....
Release date AMD Am386SX-20 20 MHz 20 MHz 5 V Watt 100-pin PQFP 1991 AMD Am386SX/SXL-25 25 MHz 25 MHz 5 V Watt 100-pin PQFP 29 April 1991 AMD Am386SX/SXL-33 33 MHz 33 MHz 5 V Watt 100-pin PQFP 1992 AMD Am386SX-40 40 MHz 40 MHz 5 V Watt 100-pin PQFP 1991
80387 coprocessor
Floating pointFloating point
In computing, floating point describes a method of representing real numbers in a way that can support a wide range of values. Numbers are, in general, represented approximately to a fixed number of significant digits and scaled using an exponent. The base for the scaling is normally 2, 10 or 16...
performance of the Am386 could be boosted with the addition of a 80387DX or 80387SX coprocessor
Coprocessor
A coprocessor is a computer processor used to supplement the functions of the primary processor . Operations performed by the coprocessor may be floating point arithmetic, graphics, signal processing, string processing, or encryption. By offloading processor-intensive tasks from the main processor,...
, although performance would still not approach that of the on-chip FPU
FPU
FPU may stand for:* Federation of Progressive Unions, a trade union center in Mauritius* Federation of Trade Unions of Ukraine* Fishermen's Protective Union, a left populist political party and later service organization in the former Dominion of Newfoundland from 1908 to the 1960s* Floating-point...
of the 486DX. This made the Am386DX a suboptimal choice for scientific applications and CAD
Computer-aided design
Computer-aided design , also known as computer-aided design and drafting , is the use of computer technology for the process of design and design-documentation. Computer Aided Drafting describes the process of drafting with a computer...
using floating point intensive calculations. However, both were niche markets in the early 1990s and the chip sold well, first as a mid-range contender, and then as a budget chip. Although motherboard
Motherboard
In 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 using the older 386 CPUs often had limited memory expansion possibilities and therefore struggled under Windows 95
Windows 95
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...
's memory requirements, boards using the Am386 were sold well into the mid-1990s; at the end as budget motherboards for those who were only interested in running MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
or Windows 3.1x
Windows 3.1x
Windows 3.1x is a series of 16-bit operating systems produced by Microsoft for use on personal computers. The series began with Windows 3.1, which was first sold during March 1992 as a successor to Windows 3.0...
applications.
The Am386 and its low-power successors were also popular choices for embedded system
Embedded system
An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...
s, for a much longer period than their life span as PC
Personal computer
A 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...
processors.