486 Central processing unit
The exposed die of an Intel 80486DX2 microprocessor.
Produced:	From 1989 to 2007
Common Manufacturers: Intel AMD
CPU Speeds:	33 Mhz to 100 Mhz
FSB Speeds:	25 Mhz to 50 Mhz
Architecture:	x86 (i386)
Sockets: Socket 1 Socket 2 Socket 3

The Intel i486 (also called 486 or 80486) is a range of 32-bit scalar Intel CISC microprocessors which is part of the Intel x86 family of processors. The i486's predecessor was the Intel 80386 processor. The first line of 486 processors was introduced in 1989 containing 1.2 million transistors (0.8 micron technology). The i486 was so named without the usual 80-prefix, because of a court ruling that prohibited trademarking numbers (like 80486). Intel dropped number-based naming altogether with the successor to the i486 – the Pentium processor. CPU redirects here. ... Image File history File links Download high resolution version (1341x1002, 803 KB) Summary Macro shot of an Intel 80486DX2 die in its packaging. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... Advanced Micro Devices, Inc. ... CPU redirects here. ... A megahertz (MHz) is one million (106) hertz, a measure of frequency. ... A megahertz (MHz) is one million (106) hertz, a measure of frequency. ... In computers, the front side bus (FSB) is a term for the physical bi-directional data bus that carries all electronic signal information between the central processing unit (CPU) and other devices within the system such as random access memory (RAM), the system BIOS, AGP video cards, PCI expansion cards... A megahertz (MHz) is one million (106) hertz, a measure of frequency. ... A megahertz (MHz) is one million (106) hertz, a measure of frequency. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... The Intel 80386 is a microprocessor which was used as the central processing unit (CPU) of many personal computers from 1986 until 1994 and later. ... Socket 1 was the second of a series of standard sockets created by Intel into which various x86 microprocessors were plugged. ... Socket 2 was one of the series of standard sockets into which various x86 microprocessors were plugged. ... Intels Socket 3 was a type of CPU socket into which various x86 microprocessors were inserted. ... 32-bit is a term applied to processors, and computer architectures which manipulate the address and data in 32-bit chunks. ... Scalar processors represent the simplest class of computer processors. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... A complex instruction set computer (CISC) is a microprocessor instruction set architecture (ISA) in which each instruction can execute several low-level operations, such as a load from memory, an arithmetic operation, and a memory store, all in a single instruction. ... A microprocessor (sometimes abbreviated µP) is a digital electronic component with transistors on a single semiconductor integrated circuit (IC). ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... Intel 80386 DX, 33MHz, foreground The Intel 80386 is a microprocessor which was used as the central processing unit (CPU) of many personal computers from 1986 until 1994 and later. ... Pentium logo, with MMX enhancement The Pentium is a fifth-generation x86 architecture microprocessor by Intel. ...

Improvements

From a software point of view, the instruction set of the i486 family is very similar to its predecessor, the Intel 80386, with the addition of only a few extra instructions. An instruction set, or instruction set architecture (ISA), describes the aspects of a computer architecture visible to a programmer, including the native datatypes, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O (if any). ... Intel 80386 DX, 33MHz, foreground The Intel 80386 is a microprocessor which was used as the central processing unit (CPU) of many personal computers from 1986 until 1994 and later. ...

From a hardware point of view, however, the architecture of the i486 is a vast improvement. It has an on-chip unified instruction and data cache, an optional on-chip floating-point unit (FPU) (DX models only), and an enhanced bus interface unit. In addition, under optimal conditions, the processor core can sustain an execution rate of one instruction per clock cycle. These improvements yield a rough doubling in performance over an Intel 80386 at the same clock rate. However, some low-end i486 models were actually slower than the highest-speed 386s, especially so with the 'SX' i486s. Diagram of a CPU memory cache A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. ... A floating point unit (FPU) is a part of a CPU specially designed to carry out operations on floating point numbers. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers and typically is controlled by device driver software. ... It has been suggested that this article or section be merged into Clock signal. ...

The 486DX2 architecture.

Image File history File links Download high resolution version (1409x994, 70 KB) The i486DX2 architecture. ... Image File history File links Download high resolution version (1409x994, 70 KB) The i486DX2 architecture. ...

Differences between the 386 and 486

• Data/Instruction Cache - An 8192-byte (8 kB) SRAM built into the processor core, designed to store the most commonly used instructions. The 386 supported an off-chip cache, but this was much slower.
• Pipelining - This allows the processor to handle a Locate-Fetch-Execute each clock cycle. The pipeline is offset meaning the execute step required information from the previous two clock cycles. A locate would feed the next fetch, the fetch would feed the next execute. The 386 needs to do each step separately.
• Improvements to MMU performance
• Integrated FPU- (DX models only) Added accelerated high end math functions.

The 486 has a 32-bit data bus and a 32-bit address bus. This requires either four matched 30-pin SIMMs or one 72-pin SIMM. The 32-bit address bus limits it 4 GB of RAM. Look up cache in Wiktionary, the free dictionary. ... MMU is the initialism (acronym) for: Manchester Metropolitan University Manned Maneuvering Unit, in astronautics Memory management unit, in computer architecture Mono Methyl Urea, in chemistry Multimedia University, a private university in Malaysia Myanmar Maritime University, a school of science and engineering under the Ministry of Transport of Myanmar Government. ... A floating point unit (FPU) is a part of a CPU specially designed to carry out operations on floating point numbers. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers. ... An address bus is (part of) a computer bus, used by CPUs or DMA-capable units for communicating the physical addresses of computer memory elements/locations that the requesting unit wants to access (read/write). ... 30- (top) and 72-pin (bottom) SIMMs. ...

The Intel project manager for the 80486 was Pat Gelsinger.

In May 2006 Intel announced that production of the 80486 would cease at the end of September 2007. [1] Although the chip had long been obsolete for personal computer applications, Intel had continued production for use in embedded systems. An embedded system is a special-purpose computer system, which is completely encapsulated by the device it controls. ...

Models

An Intel 80486DX-33 microprocessor

There are several suffixes and variants including: Image File history File linksMetadata Download high resolution version (980x1004, 670 KB)Intel_80486DX-33 This picture is taken by Weihao. ... Image File history File linksMetadata Download high resolution version (980x1004, 670 KB)Intel_80486DX-33 This picture is taken by Weihao. ...

• Intel 80486SX - a i486DX with its FPU disabled, although the earlier variants were simply normal i486s with defective FPUs. In later versions, the FPU was removed from the die to reduce its area and thus reduce cost.
• Intel 80486DX - same as above, with a working FPU.
• Intel 80486DX2 - the internal processor clock runs at twice the clock rate of the external bus clock.
• Intel 80486SX2 - same as the i486DX2, but with the FPU disabled.
• Intel 80486SL - i486SX with power conservation circuitry. Mainly for use in portable computers.
• Intel 80486SL-NM - i486SX with power conservation circuitry; SL enhanced suffix, denotes a i486 with special power conservation circuitry similar to that in the i486SL processors.
• Intel 80487 - i486DX with a slightly different pinout for use in i486SX systems as a FPU.
• Intel 80486 OverDrive - i486SX, i486SX2, i486DX2 or i486DX4. Marked as upgrade processors, some models had different pinouts or voltage handling abilities from 'standard' chips of the same speed stepping.
• Intel 80486DX4 - designed to run at triple clock rate (not quadruple as often believed; the DX3, which was meant to run at 2.5x the clock speed, was never released).

Internal clock rates included 16, 20, 25, 33, 40, 50, 66, 75 and 100 MHz, although the 100 MHz versions could be somewhat unstable. The 486DX2 66 MHz was the most widespread high-end 486 chip, while more powerful iterations such as the OverDrive and DX4 were less used in favour of the succeeding Pentium. The only 486 that ran a 50 MHz bus, the 486DX 50 MHz chip, had compatibility problems with boards and components because of this high bus speed requirement. 486DX 50 MHz was a rather unpopular chip and was quickly replaced by the clock-doubled 486 DX2 chips which ran the bus at half of the CPU clock speed. The Intel 80486SX is an Intel 486DX microprocessor with its floating-point unit (FPU) disconnected. ... Integrated circuit showing memory blocks, logic and input/output pads around the periphery A monolithic integrated circuit (also known as IC, microchip, silicon chip, computer chip or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) which has been manufactured in the surface... A floating point unit (FPU) is a part of a CPU specially designed to carry out operations on floating point numbers. ... An Intel i486DX2-66 Microprocessor, top view ... and bottom view with gold plated pins. ... It has been suggested that this article or section be merged into Clock signal. ... The Intel 80486SL is the power-saving variant of the Intel 80486DX microprocessor. ... The Intel 80487, or 487 (i487), was the floating-point arithmetic coprocessor for the Intel 486SX chips. ... Intel 80486 OverDrive processors were a category of various Intel 80486s that were produced with the designated purpose of being used to upgrade personal computers. ... The Intel DX4 is a clock-tripled 80486 microprocessor chip. ... Pentium logo, with MMX enhancement The Pentium is a fifth-generation x86 architecture microprocessor by Intel. ... An Intel i486DX2-66 Microprocessor, top view ... and bottom view with gold plated pins. ...

Competitive alternatives

486 compatible processors have been produced by other companies such as IBM, Texas Instruments, AMD, Cyrix, and Chips and Technologies. Some are almost exact duplicates in specifications and performance, some are not. The 486 was, however, covered by many of Intel's 386 patents as well as some of its own. Intel and IBM have broad cross-licenses of these patents, and AMD was granted rights to the relevant patents in the 1995 settlement of a lawsuit between the companies.[2] International Business Machines Corporation (IBM, or colloquially, Big Blue) (NYSE: IBM) (incorporated June 15, 1911, in operation since 1888) is headquartered in Armonk, New York, USA. The company manufactures and sells computer hardware, software, and services. ... Texas Instruments (NYSE: TXN), better known in the electronics industry (and popularly) as TI, is an American company based in Dallas, Texas, USA, renowned for developing and commercializing semiconductor and computer technology. ... Advanced Micro Devices, Inc. ... Cyrix corporate logo Cyrix was a CPU manufacturer that began in 1988 as a specialist supplier of high-performance math co-processors for 286 and 386 systems. ... Chips and Technologies was the first fabless semiconductor company, a model developed by its founder Gordon Campbell. ...

Platform

With regards to the 486 system platform, early 486 machines were equipped with only 16-bit and 8-bit ISA slots. Later motherboards combined ISA with the high-speed VESA Local Bus (VLB), primarily for video cards and hard drive controllers. Prior to this some motherboards came equipped with 32 bit versions of the ISA standard called: EISA. These were supplanted with VLB and later PCI. The final 486 boards came equipped with PCI and ISA, and sometimes VLB as well (though in this configuration VLB suffered performance-wise). Bus speed was determined by multipliers for ISA, but PCI and VLB bus clocks were often equal to the clock of the 486 bus (some boards had multipliers for these as well). In computer science, 16-bit is an adjective used to describe integers that are at most two bytes wide, or to describe CPU architectures based on registers, address buses, or data buses of that size. ... 8-bit refers to the number of bits used in the data bus of a computer. ... Industry Standard Architecture (in practice almost always shortened to ISA) is a computer bus standard for IBM compatible computers. ... A motherboard, also known as a mainboard, system board, or logic boards on Apple Computers, and sometimes abbreviated as mobo (generally credited to the magazine Maximum PC) is the central or primary circuit board making up a complex electronic system, such as a modern computer. ... The VESA Local Bus (usually shortened to VLB) is a local bus defined by the Video Electronics Standards Association, mostly used in personal computers based on the Intel 80486 CPU. VESA Local Bus worked alongside the ISA bus; it acted as a high-speed conduit for memory-mapped I/O... Three EISA Slots. ... 64-bit PCI expansion slots inside a Power Macintosh G4 The Peripheral Component Interconnect, or PCI Standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. ...

Later 486 boards also supported Plug-and-play, the Microsoft technology that began as a part of Windows 95 designed to make component installation easier for consumers. Plug and Play is a term used in the computer field to describe a computers ability to have new devices, normally peripherals, added to it without having to restart the computer. ... The Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... Windows 95 is a consumer-oriented graphical user interface-based operating system. ...

See also

• List of Intel microprocessors
• Motorola 68040, although not compatible, often considered the Motorola equivalent to the Intel 80486 in terms of performance.

This generational and chronological list of Intel microprocessors attempts to present all of Intels processors (µPs) from the pioneering 4-bit 4004 (1971) to the present high-end offerings, the 64-bit Itanium 2 (2002) and Pentium 4F with EM64T (2004). ... The Motorola 68040 is a microprocessor from Motorola. ... Motorola (NYSE: MOT) is an American international communications company based in Schaumburg, Illinois, a Chicago suburb. ...

References

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. The Free On-line Dictionary of Computing (FOLDOC) is an online, searchable encyclopedic dictionary of computing subjects. ... GNU logo (similar in appearance to a gnu) The GNU Free Documentation License (GNU FDL or simply GFDL) is a copyleft license for free content, designed by the Free Software Foundation (FSF) for the GNU project. ...

External links

• http://users.erols.com/chare/486.htm
• Intel 80486 images and descriptions at cpu-collection.de
• CPU-INFO: 80486, indepth processor history