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x86 CPU Reference
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This document is intended to provide some reference information on x86-compatible processors. I try to keep it as accurate as possible, but I make no claims it's complete or perfect. Almost no attention has been paid to embedded or mobile processors, as well as Intel OverDrives. Those CPUs labeled with Pentium Ratings (PRs) were listed under their real frequencies; it might be a little harder to recognise a particular model this way, but overall provides with a more clear picture. If you have a more detailed or even correct information, please drop me a note. You're free to use this reference for your needs, just give me a credit! Special thanks:
16 BITS1.1. Intel i8086 In old good days of 1978 Intel introduced i8086 -- a general-purpose processor capable of being used in so-called "personal computers". It operated with a "brand new" logic, had a 16-bit memory bus and a 20-bit address bus, thus allowing to work with 1Mb of memory mapped into 64Kb segments (16-bit offsets). However, both buses were multiplexed (i.e. only one bus could be active at any moment given). IBM, a strategic partner of Intel, soon started manufacturing PCs based on this CPU. Several manufacturers (Compaq, Columbia, Kayro, etc.) also built machines with i8086 inside, and claimed them to be "IBM-compatible" (however, their BIOSes weren't totally compatible with IBM's one). About 14.9 million units were sold (including clones). 1.2. Intel i8088 Later Intel introduced a stripped version of i8086, with a 8-bit memory bus, and called it i8088. Since i8086 was priced somewhat highly, there was a significant demand in a cheaper product, and that was i8088 to stand for. This CPU was widely and successfully used in IBM PC/XT (Personal Computer/eXtended Technology) and compatibles in early 1980s (in a matter of fact, first commercially-available PC of x86 architecture was built by IBM using i8088, in 1981). About 20.5 million units were sold (including clones). 1.3. Intel i80186 and i80188 These chips were successors to i8086\i8088, but weren't used widely in PCs because of their all-in-one nature. The core logic was updated with all the real mode instructions of future i80286, for more convenient low-level programming; was added a fault protection algorithm (original i8086\i8088 would simply hang upon executing an unknown instruction). These chips included a number of peripherals that were usually located onto a motherboard:
But, these chips achieved a great success in the world of embedded processors, and were used in various electronic devices (portables, hard disk controllers, modems, etc.). For example, US Robotics used 20MHz and 25MHz versions of i80186 in Courier V.Everything modems, in late 1990s. 1.4. Intel i80286 i80286 expanded possibilities of i8086\i8088 by implementing some new features: it could operate both in the real mode (to keep compatibility with i8086), and the protected mode, addressing up to 16Mb of the physical memory because of the increased address bus width (now 24-bit). New instructions were added into the logic, mostly to drive the protected mode. The first commercially available machine built with i80286 was from IBM PC/AT (Advanced Technology) line, in August of 1984. About 36.8 million units were sold (including clones). 1.5. Clones In early 1980s Intel's manufacturing facilities weren't capable to satisfy rapidly growing market demand on x86-compatible processors. On the other hand, Intel didn't want computer building companies to use CPUs of different architectures than x86 (mostly, Motorola 68K); thereby, Intel licensed manufacturing rights to several semiconductor companies such as AMD, Harris, Hitachi, Siemens, IBM, and probably others. Their CPUs were exact clones to i8086\i8088, i80186\i80188 and i80286:
1.6. NEC V30 and V20 These chips were first non-licensed clones of Intel i8086 (V30) and i8088 (V20). Intel sued NEC, claiming that it violated the copyright on i8086 and i8088, but lost finally: verdict said that the CPU microcode could be copyrighted, but Intel forfeited all rights because hadn't labeled the processors as such. There were several modifications of these chips (V20H\V30H, V25\V35, V40\V50, V45\V55). These CPUs included the full i80186 instruction set, and performed about 20% faster i8086\i8088 when running at the same clock speed. Also, they could run in the native Z80 mode (i.e. to execute directly software written for Zilog Z80 CPUs). 1.7. Chips & Technologies F8680 This chip was targeted to the notebook and subnotebook market. It consisted of an i80186-compatible CPU, a CGA-compatible display adapter, a universal asynchronous receiver and transimitter, and a PCMCIA circuitry. Due to the optimised internal architecture, it offered performance comparable to i80286.
32 BITS: NON-SCALAR2.1. Intel i386DX i386DX (Double word eXternal, about memory bus) was designed with the 32-bit architecture in mind: a 32-bit non-pipelined IEU (IADD, IMUL, IDIV) with a 64-bit barrel shifter and eight 32-bit general purpose registers, a 32-bit AGU (load\store), and a 32-bit instruction decoder\fetcher. Since the core didn't contain a FPU, a mathprocessor (i387 or compatible) could be installed separately. As of the memory management, in addition to a segmentation unit (like in the previous models) it also incorporated a paging unit, allowing manipulations of the physical address space using 4Kb pages. Was interfaced to two independent 32-bit buses, the memory and the address. When in the protected mode, it could address up to 4Gb of the physical memory. It also supported a protected mode extention called Virtual 8086 (V86), for better multitasking (to set up virtual areas in memory). At the same time, i386DX was completely backwards compatible, being able to execute any 16-bit code. Interesting, but the first available commercially machine with i386DX inside was manufactured by Compaq, not IBM. About 15.5 million units were sold.
2.2. Intel i386SX i386SX (Single word eXternal, about the memory bus) was marketed as a mainstream CPU. It had the same core compared to i386DX, but the width of both memory and address buses was reduced (to 16-bit and 24-bit, respectively). About 21.9 million units were sold. 2.3. Intel i386SL The low-power version of i386SX, with both cache and memory controllers integrated. Designed exclusively for notebooks and other portables. Intel's second attempt to produce an all-in-one chip since i80186. About 1.8 million units were sold. 2.4. AMD 386 series In the middle of 1980s AMD launched its own microprocessor department, and began designing a 386-class processor. It took several years to release Am386DX, an alternative to i386DX. However, there were some legal issues, because AMD used Intel's microcode without a license.
2.5. IBM 386 series IBM manufactured x86-family CPUs due to a joint-development agreement with Intel, which allowed IBM to produce proprietary cores based upon Intel's ones by optimising some frequently-used instructions, adding new, etc. So, all these CPUs were based on the i386 core. IBM also manufactured Cyrix CPUs, since September of 1993.
2.6. Cyrix 386 series In early 1990s Cyrix Corp. (from Richardson, TX) entered the microprocessor market with both proprietarly-designed 386-class CPU core and microcode. Cyrix's 386 CPUs were marketed as "486", but in fact they were just enhanced with the 486 command set and the little built-in cache. Later appeared that the microcode wasn't completely compatible with Intel's one, and that caused numerous software incompatibilities. Since Cyrix had no manufacturing facilities of its own, so all processors were produced on semiconductor factories of Texas Instruments and SGS-Thomson. Instead of fees, certain amounts of CPUs were sold directly by the manufacturers, and under their brands. IBM started producing Cyrix's chips since September of 1993.
2.7. Chips & Technologies 386 series Several 386-class CPUs were manufactured by Chips & Technologies, using the proprietary microcode:
2.8. Texas Instruments 386 series Texas Instruments manufactured proprietary Potomac series 386-class CPUs based upon the core from Cyrix but with some enhancements, as well as true Cyrix ones. Regardless of their "486" nomenclature, they had a non-pipelined 386 core.
1. First 16MHz i386DX had a clock trouble and were sold as 12MHz. 2. 16 and 20MHz i386SL required 3.3V while 25 and 33MHz -- 5V.
32 BITS: SCALAR3.1. Intel i486DX (P4) i486DX was the first x86-family processor with both FPU and cache (8Kb) integrated into the core. Also it was the first scalar processor, able to execute most integer instructions in the single-clock mode (1 command per 1 clock tick), because of the 5-stage integer pipeline driven by certain RISC techniques. All these improvements resulted in about 100% integer performance increase compared to equally-clocked i386DX. However, the built-in FPU remained non-pipelined. 3.2. Intel i486SX (P23) A low-priced version of i486DX, without FPU. Some initial models had no cache as well. Some models had the built-in FPU, but disabled; most models had no FPU circuitry at all. For hardware floating-point calculations it required a mathprocessor (i487), which was nothing but a fully-featured i486DX with a slightly different pinout; once installed it turned i486SX into indefinite sleep, and performed well for both. 3.3. Intel i486SL Intel's third attempt to produce an all-in-one chip; the core of i486DX + three controllers: memory, ISA and PI (Peripheral Interconnect bus). Like before, exclusively for notebooks and other portables. Of course, i486DX pin-incompatible. 3.4. Intel i486DXL and i486SXL Nothing but power-saving modifications of i486DX and i486SX, respectively. 3.5. Intel i486DX2 (P24) A clock-doubled version of i486DX: the first x86-family CPU to run a FSB at half a core speed. 3.6. Intel i486SX2 A clock-doubled version of i486SX. 3.7. Intel i486DX4 (P24C) A clock-tripled variant of i486DX, with the larger cache. Could run with clock-doubling (CLKMUL pin). 3.8. AMD 486 series Two years after Am386, AMD started manufacturing Am486-family CPUs. All initial models were complete clones of i486 ones, with the same core and microcode. Later, due to numerous legal issues with Intel, AMD invented the proprietary 486-class microcode, and implemented it.
3.9. IBM 486BLX, 486BLX2 and 486BLX3 (Blue Lightning) These CPUs were manufactured by IBM under the same joint-development agreement with Intel as 386 series. Blue Lightning CPUs were designed as i486SX with a 16Kb cache, and with i386DX-compatible pinout. 486BLX2 and 486BLX3 ran with clock-doubling and clock-tripling, respectively. In a matter of fact, they were the fastest CPUs to fit the 386 PGA socket. 3.10. Cyrix 486 series About a year after releasing the proprietary 386 core, Cyrix announced a new one, and released a number of true 486-class CPUs.
3.11. UMC U5SX, U5DX and U5SXL United Microelectronics Corporation (UMC), a Taiwan semiconductor company, started its own line of 486-class CPUs. But since it violated some Intel's patents, these CPUs were restricted for sale on the US market. Pin-compatible with i486SX (U5SX) and i486DX (U5DX); U5SXL was a low-voltage (3.3V) version of U5SX. A mathprocessor (U5) could be installed with U5SX and U5SXL.
3. 50MHz model was introduced in June of 1991, but due to numerous overheating problems and overall system instability was recalled. 4. 80MHz Am486DX2 was released in September of 1994. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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