i486
SQFP | |
History | |
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Predecessor(s) | Intel 386 |
Successor(s) | Pentium/i586 (P5) |
Support status | |
Unsupported |
The
.It was the first tightly-
When it was announced, the initial performance was originally published between 15 and 20 VAX MIPS, between 37,000 and 49,000 dhrystones per second, and between 6.1 and 8.2 double-precision megawhetstones per second for both 25 and 33 MHz version.[2] A typical 50 MHz i486 executes 41 million instructions per second Dhrystone MIPS and SPEC integer rating of 27.9.[4] It is approximately twice as fast as the i386 or i286 per clock cycle. The i486's improved performance is thanks to its five-stage pipeline with all stages bound to a single cycle. The enhanced FPU unit on the chip was significantly faster than the i387 FPU per cycle. The Intel 80387 FPU ("i387") was a separate, optional math coprocessor that was installed in a motherboard socket alongside the i386.
The i486 was succeeded by the original Pentium. Orders were discontinued for the i486 on March 30, 2007 and the last shipments were on September 28, 2007.[5]
History
The concept of this microprocessor generation was discussed with Pat Gelsinger and John Crawford shortly after the release of 386 processor in 1985. The team started the computer simulation in early 1987. They finalized the logic and microcode function during 1988. The team finalized the database in February 1989 until the tape out on March 1. They received the first silicon from the fabrication on March 20.[6]
The i486 was announced at Spring Comdex in April 10, 1989.[2] At the announcement, Intel stated that samples would be available in the third quarter and production quantities would ship in the fourth quarter.[7] The first i486-based PCs were announced in late 1989.[8]
In fall of 1991, Intel introduced the 50-MHz i486 DX using the three layer 800-nm process CHMOS-V technology. They were available for USD $665 in 1,000-unit quantities.[9]
In that season, Intel introduced low-power 25 MHz Intel486 DX microprocessor. This one was available for USD $471. Also, there were low-power 16, 20, and 25 MHz Intel486 SX microprocessors. They were available USD $235, USD $266, and USD $366 for these frequency range respectfully. All pricing were in quantities of 1,000 pieces. These low-power microprocessor reduces between 50 and 75% of power consumption with similar regular version of these CPUs.[10]
The first major update to the i486 design came in March 1992 with the release of the clock-doubled 486DX2 series.[11] It was the first time that the CPU core clock frequency was separated from the system bus clock frequency by using a dual clock multiplier, supporting 486DX2 chips at 40 and 50 MHz. The faster 66 MHz 486DX2-66 was released that August.[11]
The fifth-generation Pentium processor launched in 1993, while Intel continued to produce i486 processors, including the triple-clock-rate 486DX4-100 with a 100 MHz clock speed and a L1 cache doubled to 16 KB.[11]
Earlier, Intel had decided not to share its 80386 and 80486 technologies with AMD. However, AMD believed that their technology sharing agreement extended to the 80386 as a derivative of the 80286.[11] AMD reverse-engineered the 386 and produced the 40 MHz Am386DX-40 chip, which was cheaper and had lower power consumption than Intel's best 33 MHz version.[11] Intel attempted to prevent AMD from selling the processor, but AMD won in court, which allowed it to establish itself as a competitor.[12]
AMD continued to create clones, releasing the first-generation Am486 chip in April 1993 with clock frequencies of 25, 33 and 40 MHz. Second-generation Am486DX2 chips with 50, 66 and 80 MHz clock frequencies were released the following year.[11] The Am486 series was completed with a 120 MHz DX4 chip in 1995.[11]
AMD's long-running 1987 arbitration lawsuit against Intel was settled in 1995, and AMD gained access to Intel's 80486 microcode.[11] This led to the creation of two versions of AMD's 486 processor - one reverse-engineered from Intel's microcode, while the other used AMD's microcode in a clean room design process. However, the settlement also concluded that the 80486 would be AMD's last Intel clone.[11]
Another 486 clone manufacturer was
In 1995, both Cyrix and AMD began looking at a ready market for users wanting to upgrade their processors. Cyrix released a derivative 486 processor called the 5x86, based on the Cyrix M1 core, which was clocked up to 120 MHz and was an option for 486 Socket 3 motherboards.[11][12] AMD released a 133 MHz Am5x86 upgrade chip, which was essentially an improved 80486 with double the cache and a quad multiplier that also worked with the original 486DX motherboards.[11] Am5x86 was the first processor to use AMD's performance rating and was marketed as Am5x86-P75, with claims that it was equivalent to the Pentium 75.[12] Kingston Technology launched a 'TurboChip' 486 system upgrade that used a 133 MHz Am5x86.[11]
Intel responded by making a Pentium OverDrive upgrade chip for 486 motherboards, which was a modified Pentium core that ran up to 83 MHz on boards with a 25 or 33 MHz front-side bus clock. OverDrive wasn't popular due to speed and price.[11] The 486 was declared obsolete as early as 1996, with a Florida school district's purchase of a fleet of 486DX4 machines in that year sparking controversy. New computers equipped with 486 processors in discount warehouses became scarce, and an IBM spokesperson called it a "dinosaur".[13] Even after the Pentium series of processors gained a foothold in the market, however, Intel continued to produce 486 cores for industrial embedded applications. Intel discontinued production of i486 processors in late 2007.[11]
Improvements
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The
The i486's performance architecture is a vast improvement over the i386. It has an on-chip unified instruction and data
ALU reg,reg
and ALU reg,im
) could sustain single-clock-cycle throughput (one instruction completed every clock). In other words, it was running about 1.8 clocks per instruction.[6] These improvements yielded a rough doubling in integer ALU performance over the i386 at the same clock rate. A 16 MHz i486 therefore had performance similar to a 33 MHz i386. The older design had to reach 50 MHz to be comparable with a 25 MHz i486 part.[d]Differences between i386 and i486
- An 8 level 2 cachebecause i386 had no internal level 1 cache).
- An enhanced external bus protocol to enable cache coherency and a new burst mode for memory accesses to fill a cache line of 16 bytes within five bus cycles. The 386 needed eight bus cycles to transfer the same amount of data.
- Tightly coupledpipeliningcompletes a simple instruction like ALU reg,reg or ALU reg,im every clock cycle (after a latency of several cycles). The i386 needed two clock cycles.
- Integrated i387combination.
- Improved MMU performance.
- New instructions: XADD, BSWAP, CMPXCHG, INVD, WBINVD, INVLPG.
Just as in the i386, a flat 4 GB memory model could be implemented. All "segment selector" registers could be set to a neutral value in
On a typical PC
Models
Intel offered several suffixes and variants (see table). Variants include:
- 80387FPU.
- i486SL-NM: i486SL based on i486SX.
- i487SX (P23N): i486DX with one extra pin sold as an FPU upgrade to i486SX systems; When the i487SX was installed, it ensured that an i486SX was present on the motherboardbut disabled it, taking over all of its functions.
- i486 OverDrive (P23T/P24T): 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. Fitted to a coprocessor or "OverDrive" socket on the motherboard, they worked the same as the i487SX.
The maximal internal clock frequency (on Intel's versions) ranged from 16 to 100 MHz. The 16 MHz i486SX model was used by
One of the few i486 models specified for a 50 MHz bus (486DX-50) initially had overheating problems and was moved to the 0.8-
More powerful i486 iterations such as the OverDrive and
Model CPU/bus
clock speedVoltageL1 cache*Introduced Notes i486DX (P4) 20, 25 MHz
33 MHz
50 MHz5 V 8 KB WT April 1989
May 1990
June 1991The original chip without clock multiplier i486SL 20, 25, 33 MHz 5 V or 3.3 V 8 KB WT November 1992 Low-power version of the i486DX, reduced VCore, SMM (System Management Mode), stop clock, and power-saving features — mainly for use in portable computers i486SX (P23) 16, 20, 25 MHz
33 MHz5 V 8 KB WT September 1991
September 1992An i486DX with the FPU part disabled; later versions had the FPU removed from the die to reduce area and hence cost. i486DX2 (P24) 40/20, 50/25 MHz
66/33 MHz5 V 8 KB WT March 1992
August 1992The internal processor clock runs at twice the clock rate of the external bus clock i486DX-S (P4S) 33 MHz; 50 MHz 5 V or 3.3 V 8 KB WT June 1993 SL Enhanced 486DX i486DX2-S (P24S) 40/20 MHz,
50/25 MHz,
(66/33 MHz)5 V or 3.3 V 8 KB WT June 1993 SL Enhanced 486DX2 i486SX-S (P23S) 25, 33 MHz 5 V or 3.3 V 8 KB WT June 1993 SL Enhanced 486SX i486SX2 50/25, 66/33 MHz 5 V 8 KB WT March 1994 i486DX2 with the FPU disabled IntelDX4 (P24C) 75/25, 100/33 MHz 3.3 V 16 KB WT March 1994 Designed to run at triple clock rate (not quadruple, as often believed; the DX3, which was meant to run at 2.5× the clock speed, was never released). DX4 models that featured write-back cache were identified by an "&EW" laser-etched into their top surface, while the write-through models were identified by "&E". i486DX2WB (P24D) 50/25 MHz,
66/33 MHz5 V 8 KB WB October 1994 Enabled write-back cache. IntelDX4WB 100/33 MHz 3.3 V 16 KB WB October 1994 i486DX2 (P24LM) 90/30 MHz,
100/33 MHz2.5–2.9 V 8 KB WT 1994 i486GX up to 33 MHz 3.3 V 8 KB WT Embedded ultra-low-power CPU with all features of the i486SX and 16-bit external data bus. This CPU is for embedded battery-operated and hand-held applications.
*WT = write-through cache strategy, WB = write-back cache strategy
Other makers of 486-like CPUs
Processors compatible with the i486 were produced by companies such as IBM, Texas Instruments, AMD, Cyrix, UMC, and STMicroelectronics (formerly SGS-Thomson). Some were clones (identical at the microarchitectural level), others were clean room implementations of the Intel instruction set. (IBM's multiple-source requirement was one of the reasons behind its x86 manufacturing since the 80286.) The i486 was, however, covered by many Intel patents, including from the prior i386. Intel and IBM had 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.[14]
AMD produced several clones using a 40 MHz bus (486DX-40, 486DX/2-80, and 486DX/4-120) which had no Intel equivalent, as well as a part specified for 90 MHz, using a 30 MHz external clock, that was sold only to OEMs. The fastest running i486-compatible CPU, the Am5x86, ran at 133 MHz and was released by AMD in 1995. 150 MHz and 160 MHz parts were planned but never officially released.
Cyrix made a variety of i486-compatible processors, positioned at the cost-sensitive desktop and low-power (laptop) markets. Unlike AMD's 486 clones, the Cyrix processors were the result of clean-room reverse engineering. Cyrix's early offerings included the 486DLC and 486SLC, two hybrid chips that plugged into 386DX or SX sockets respectively, and offered 1 KB of cache (versus 8 KB for the then-current Intel/AMD parts). Cyrix also made "real" 486 processors, which plugged into the i486's socket and offered 2 or 8 KB of cache. Clock-for-clock, the Cyrix-made chips were generally slower than their Intel/AMD equivalents, though later products with 8 KB caches were more competitive, albeit late to market.
The Motorola 68040, while not i486 compatible, was often positioned as its equivalent in features and performance. Clock-for-clock basis the Motorola 68040 could significantly outperform the Intel chip.[15][16] However, the i486 had the ability to be clocked significantly faster without overheating. Motorola 68040 performance lagged behind the later production i486 systems.[citation needed]
Motherboards and buses
Early i486-based computers were equipped with several
Some motherboards came equipped with a
Late i486 boards were normally equipped with both PCI and ISA slots, and sometimes a single VLB slot. In this configuration, VLB or PCI throughput suffered depending on how buses were bridged. Initially, the VLB slot in these systems was usually fully compatible only with video cards (fitting as "VESA" stands for
One of the earliest complete systems to use the i486 chip was the Apricot VX FT, produced by British hardware manufacturer Apricot Computers.[17] Even overseas in the United States it was popularized as "The World's First 486".
Later i486 boards supported
Obsolescence
The
Computers based on the i486 remained popular through the late 1990s, serving as low-end processors for entry-level PCs. Production for traditional desktop and laptop systems ceased in 1998, when Intel introduced the
In the general-purpose desktop computer role, i486-based machines remained in use into the early 2000s, especially as Windows 95 through 98 and Windows NT 4.0 were the last Microsoft operating systems to officially support i486-based systems.[18][19] Windows 2000 could run on a i486-based machine, although with a less than optimal performance, due to the minimum hardware requirement of a Pentium processor.[20] However, as they were overtaken by newer operating systems, i486 systems fell out of use except for backward compatibility with older programs (most notably games), especially given problems running on newer operating systems. However, DOSBox was available for later operating systems and provides emulation of the i486 instruction set, as well as full compatibility with most DOS-based programs.[21]
The i486 was eventually overtaken by the Pentium for
See also
- List of Intel microprocessors
- Motorola 68040, although not compatible, was often positioned as the Motorola equivalent to the Intel 486 in terms of performance and features.
- VL86C020, ARM3core of similar time frame and comparable MIPS performance on integer code (25 MHz for both), with 310,000 transistors (in a 1.5 µm process) instead of 1 million
Notes
- ^ AMD versions up to 120 and 160 MHz
- ^ RISC-like" ones, although the most complex also used some dedicated microcodecontrol.
- ^ Simple instructions spend only a single clock cycle at each pipeline stage.[b]
- ^ The pre-DX2 i486 parts did not use a clock multiplier and are therefore comparable to a twice-higher clocked 386/286.
- ^ In general, 8-bit ISA slots in these systems were implemented just by leaving off the shorter "C"/"D" connector of the slot, though the copper traces for a 16-bit slot were still there on the motherboard; the computer could tell no difference between an 8-bit ISA adapter in such a slot and the same adapter in a 16-bit slot, and there were still enough 8-bit adapters in circulation that vendors figured they could save money on a few connectors this way. Also, leaving off the 16-bit extension to the ISA connector allowed use of some early 8-bit ISA cards that otherwise could not be used due to the PCB "skirt" hanging down into that 16-bit extension space. IBM was the first to do this in the IBM AT.
Further reading
- Gamer, Brassic (January 1, 2023). "The Brassic Gamer: The (Almost) Definitive 486DX/50 Article". The Brassic Gamer. Retrieved January 3, 2023.
References
- ^ "Product Change Notification" (PDF). May 2, 2006. Archived from the original (PDF) on October 9, 2006.
- ^ a b c d Lewnes, Ann, "The Intel386 Architecture Here to Stay", Intel Corporation, Microcomputer Solutions, July/August 1989, page 2
- ^ a b c Intel (July 1997). Embedded Intel486 Processor Hardware Reference Manual (273025-001).
- ^ Chen, Allan, "The 50-MHz Intel486 Microprocessor", Intel Corporation, Microcomputer Solutions, September/October 1991, page 2
- ^ "Product Change Notification" (PDF). May 2, 2006. Archived from the original (PDF) on October 9, 2006.
- ^ a b Chen, Allan, "Designing A Mainframe on a Chip: Interview with the i486 Microprocessor Design Team", Intel Corporation, Microcomputer Solutions, July/August 1989, page 12
- ^ 486 32-bit CPU breaks new ground in chip density and operating performance. (Intel Corp.) (product announcement) EDN | May 11, 1989 | Pryce, Dave
- ^ Lewis, Peter H. (October 22, 1989). "THE EXECUTIVE COMPUTER; The Race to Market a 486 Machine". The New York Times. Retrieved May 5, 2010.
- ^ Chen, Allan, "The 50-MHz Intel486 Microprocessor", Intel Corporation, Microcomputer Solutions, September/October 1991, page 2
- ^ Intel Corporation, "New Product Focus: Components: Modified Chips Cuts Portable Power Consumption", Microcomputer Solutions, November/December 1991, page 10
- ^ ISSN 0725-4415.
- ^ a b c d Lilly, Paul (April 14, 2009). "A Brief History of CPUs: 31 Awesome Years of x86". PC Gamer. Retrieved August 7, 2021.
- ^ Chauvet, Berenice D. (July 15, 1996). "School buys outdated computer model". Sun Sentinel. Tribune Publishing. Archived from the original on July 2, 2021.
- ^ "AMD-Intel Litigation History". yannalaw.com.
- ^ "CISC: The Intel 80486 vs. The Motorola MC68040". July 1992. Retrieved May 20, 2013.
- ^ 68040 Microprocessor Archived February 16, 2012, at the Wayback Machine
- ^ Lavin, Paul; Nadeau, Michael E. (September 1989). "The 486s Are Here". Byte. pp. 95–98. Retrieved April 30, 2022.
- ^ "Minimum Hardware Requirements for a Windows 98 Installation". January 24, 2001. Archived from the original on December 5, 2004.
- ^ "Windows NT 4.0 Workstation" (in German). WinHistory.de.
- ^ "WORLD RECORD*: Windows 2000 running on Intel i486 SX 25 MHz". YouTube. July 29, 2013.
- ^ "System Requirements". DOSBox.com.
- ^ Tony Smith (May 18, 2006). "Intel cashes in ancient chips. i386, i486, i960 finally for the chop". HARDWARE. Archived from the original on August 13, 2011. Retrieved May 20, 2012.