Four. Eight. Six
It was the first mainstream CPU to hit the one million transistor mark and marked a huge turning point in PC performance at the time
Today’s PC CPU market is a well-oiled manufacturing and marketing machine, with new iterations appearing yearly, almost like clockwork. In fact, any slide in launch date is guaranteed to make news. Yet, wind the clock back to 1989 and the four-year wait for new PC tech was finally over, as Intel launched one of its most important processors. It’s the first mainstream CPU to crack the one-million transistor mark, the first chip to feature an on-board floating-point unit (FPU) and will go on to become joint-first x86 CPU to break the 100MHz barrier. It will also be embroiled in one of the most fiercely contested technology patent/antitrust battles in history. It is the Intel 80486 processor.
The need for speed
By the late-1980s, the future of IBM’s ‘personal computer’ concept was assured. Its rapidly-growing combination of software and ‘IBM-compatible’ clone machines had dealt a hammer-blow to the 8-bit home computer market. Intel’s 80386 CPU of 1985 had also been a roaring success – not least for nascent PC brand Compaq. Having launched the PC in 1981, IBM would always be the PC’s spiritual home. However, Compaq’s release of the Deskpro 386, the first 80386 computer, in 1986 signalled a seismic shift in who had actual control of the PC market. The 80386 chip delivered to the PC its first taste of 32-bit processing that would power the industry for more than 20 years. But despite its success, it was still a long way from the processor architecture we’d recognise today.
The 80386 produced a 50% jump in Millions of Instructions Per Second (MIPS)/MHz performance over the 80286 CPU (0.33 vs 0.21). However, with no on-board floating-point unit (FPU), no on-board cache RAM and growing demand for more performance, the 386’s 275,000 transistors had little left to give.
The arrival of the 80486 in April 1989 provided only a minor nudge in advancing the 80386 instruction set, but it packed a
sizeable wallop for speed. The launch chip ran at a comparatively sedate 25MHz, yet blitzed the higher-clocked 33MHz 80386 CPU in performance tests. By delivering the first on-board L1 cache RAM (a modest 8KB), plus the first integrated FPU, the 80486 more than doubled the average MIPS/MHz performance of the 80386, peaking at 1MIPS/ MHz for the first time. The fastest 80386 then available, the 386DX-33, delivered just under 10MIPS of performance. Those who could afford the 25MHz 80486 (the 486 cost nearly three times the 386 at time of launch) could tap into an average 20MIPS, peaking at 25MIPS.
The 80486 had a number of other architecture tricks up its sleeve also, including faster burst-mode memory loading that filled up 16 bytes of cache inside five clock cycles, three cycles faster than its predecessor. Like the 80386, its 32-bit addressing enabled the 80486 to handle 4GB of RAM, but with RAM prices as they were, most systems were lucky to see 16MB of RAM. Nevertheless, the 80486 would give many users their first taste of the future, through Microsoft’s new Windows 3.1, as well as 3D gaming, via new titles such as Wolfenstein 3D. Many would also eventually be upgraded to Windows 95.
Share and share alike
IBM’s decision to design a new ‘personal computer’ using only off-the-shelf components from multiple suppliers – and then allow key partners, Intel and Microsoft, to on-sell their components to other brands – brought the phrase ‘IBMcompatible’ to every computer buyer’s lexicon. As long as a computer was ‘IBM-compatible’, it had ready-access to a fastgrowing wealth of software. Software incompatibility was the scourge of the ‘80s home computer user and ‘IBMcompatible’ revolutionised the market.
The original 1981 IBM 5150 PC was an instant hit from the start and ‘Big Blue’ couldn’t make them fast enough. However, with its huge success, supply chain worries were never far from mind for IBM and in awarding Intel the contract to supply CPUs, IBM also required Intel to bring in a second source to supply chips in the event that Intel couldn’t keep up. Intel chose AMD, the deal giving AMD access to the Intel 8086/88 and new 80286 processor technology. However, it was a partnership that would eventually sour into one of the fiercest technology legal battles in history.
IBM was Intel’s major customer in those early years and IBM owned the PC market. But while IBM-compatibility killed off the 8-bit home computer market, it also loosened IBM’s grip on the
PC market as competitors, such as Compaq, began to successfully muscle in, especially following Intel’s launch of the 80386 in 1985. Compaq’s Deskpro 386 launched the following year was a watershed moment in this new IBM-compatible world, as consumers began to realise the CPU inside the box mattered more than the brand on the outside of the box. What’s more, having sole effective control of CPU development, Intel found itself with a winning hand – and was ready to play it.
Don’t mention the war
With IBM’s grip on the market loosening and Intel’s tightening, Intel chose not to share with AMD details of its new 80386 jewel.
AMD claimed this contravened their existing technology-sharing arrangement and sought legal arbitration in 1987. Astonishingly, both companies would continue to square off in the courts for much of the next 22 years before Intel paid AMD $US1.25billion as part of a final settlement, ending the war in November 2009. Forget ‘Apple v Samsung’ – ‘Intel v AMD’ remains the gold standard for longevity of tech legal battles. What makes it all the more surprising is that the founders of Intel and AMD had all at one time worked at pioneering chip company, Fairchild Semiconductor – Gordon Moore and Robert Noyce left Fairchild and founded Intel in 1968, while Jerry Sanders left and started AMD the following year.
Intel Inside
The 80486 design was also responsible for innovations that are part of the PC fabric today. Aside from its integrated FPU and L1 cache, the first significant performance update arrived in March 1992 with the release of the 486DX2 series. This marked the first time a CPU core clock speed was decoupled from the front-side system bus and clocked at a higher multiple. Thanks to this double-clock multiplier, 486DX2-40 and -50 chips could drop in place of the original (now-designated ‘486DX’) 5-volt parts and deliver more speed. The hugely popular 486DX2-66 arrived in August that year.
Despite launching the new fifth-generation Pentium CPU in 1993, Intel continued to release new 486 parts with the DX4series in early 1994. The new triple-clock-rate DX4-100 doubled the L1 cache RAM to 16KB, with clock speeds reaching 100MHz for the first time alongside the new Pentium-100. The 80486 was also the initial focus of the famous ‘Intel Inside’ market campaign launched in 1991.
Attack of the clones
The decision not to share its 80386 tech with AMD gave Intel a free swing at the booming PC market. However, AMD believed its previous tech-sharing agreement covered the 80386, as a derivative of the 80286. So, AMD reverse-engineered its own ‘Am386’ chip. The process reportedly took 18 months but with further legal woes, the first chips weren’t shipped until 1991. Still, they were a success, with the 40MHz part faster than Intel’s best 33MHz version, while lower in power consumption and price.
AMD’s first-generation Am486 was also a clone of the Intel design, with the launch ‘Am486DX’ chips appearing in April 1993 as 25, 33 and 40MHz models. Second-gen ‘DX2’ units appeared at 50, 66 and 80MHz the following year and topped 120MHz for the third-gen ‘DX4’ in 1995.
However, the path to market for AMD’s 486 efforts was also anything but smooth. AMD’s original 1987 arbitration claim blew out into an eight-year legal war between the two chipmakers. While AMD won the case brought by Intel over the Am386, the 80486 battle dragged on before the two antagonists settled in early 1995, with AMD gaining access to Intel 80486 microcode. This reportedly led to two versions of AMD’s 486 – one cloned from Intel microcode, another using AMD microcode via a ‘cleanroom design’ process. Importantly for Intel, the settlement confirmed the 80486 would be the last Intel CPU cloned by AMD.
Enter Cyrix
In a parallel universe, the Intel 486 also caught the eye of recently-minted Cyrix Corporation, which had to this point specialised in co-processor chips for 80286/386 systems. Cyrix was a fab-less chipmaker, relying on SGS-Thomson (now ST Microelectronics), Texas Instruments and IBM to make its chips. The first Cyrix 486SLC/ DLC versions of the 80486 appeared in 1992 loaded into an 80386 package. With PCs far more expensive than today, a ready market existed for users
wanting to keep their current system and just upgrade the processor. The Cyrix 486xLC chips, however, with only 1KB of L1 cache and no FPU, couldn’t match the genuine Intel 486 versions. However, Cyrix released Cx486DX and DX2 versions in 1993 that were closer to Intelequivalents. Nevertheless, Intel and Cyrix sued each other, with claims of antitrust behaviour against the former and patent infringement by the latter. By January 1994, existing license deals between Intel and chipmakers Texas Instruments and SGS-Thomson delivered a court victory for Cyrix, which also dropped the antitrust claim.
Meanwhile, the arrival of the Intel Pentium in 1993 with its new CPU socket left increasing numbers of 486 users looking for alternatives. Buoyed by its 1994 legal win, Cyrix became a specialist at the CPU upgrade market, releasing its ‘5x86’ in 1995, with versions clocking at up to 120MHz as a drop-in replacement for 486 systems operating at a 3.3V voltage. The Cyrix 5x86 was a stripped-down power-efficient Pentiumalternative based on its own ‘M1’ core that would go on to power its popular ‘6x86’ chips the following year. The 5x86 delivered performance levels up to a Pentium-75.
After settling its case with Intel in 1995, AMD also had success at the upgrade market, launching the ‘Am5x86’ in November that year. Essentially a 133MHz souped-up 80486, it offered twice the L1 cache and a built-in X4 multiplier to work on original DX boards. Memory brand Kingston Technology launched its shortlived ‘TurboChip’ CPU upgrade range with a 133MHz Am5x86 for 486 systems.
Not surprisingly, Intel saw the trade AMD and Cyrix were doing in upgrades and pulled out its big gun, launching the Pentium OverDrive in 1995. This was a modified Intel Pentium core with a 2.5x-clock multiplier inside an 80486 package, capable of running on boards with a 25 or 33MHz front-side bus at either 5V or 3.3V. Unfortunately, with a top speed of only 83MHz, these OverDrive chips struggled on both speed and price.
How much?
By today’s standards, PCs in the early-90s weren’t cheap. A 486DX2-66 desktop with VGA monitor, 4MB of RAM, 320MB hard drive and dual-speed CD-ROM from brands likes Olivetti or Compaq sold for around $3,500. That said, one of the first PCs I reviewed was a Pentium-133/Windows 95 desktop PC in late-1995 selling for a cool $7,800.
However, one of IBM’s most important decisions from a consumer perspective in developing the ‘personal computer’ concept was to allow Microsoft and Intel to on-sell their tech to other brands. It meant anyone with sufficient knowledge and intestinal fortitude could set themselves up as a PC maker – and many started out this way as one or two-man shows, including iconic brands Gateway and Dell. Buying from these smaller builders could save you up to 40%, dropping the price of a $3,000 big-name-brand 486DX2/66 system to as little as $1,800 and often with more features.
The 486 today
So, after more than 30 years, how does the 80486 stack up against today’s wonder-chips? There’s no doubt the 486’s 1MIPS/MHz performance is pretty modest, particularly up against AMD’s current Ryzen Threadripper 3990X with its 64 cores and claimed 500MIPS per core. Nevertheless, you’ll still find a computer on the market today with 486-equivalent performance.
Say hello to the STM32F103C8T6, a 32-bit Cortex-M3 microcontroller designed by smartphone CPU company ARM and manufactured by ST Microelectronics. It clocks in at 72MHz with a 1.25MIPS/MHz performance rating and I use it in my home-brew Arduino projects. It’s available on Ebay today for just $5. Download the Arduino IDE software (www. arduino.cc) and you can code it using the C++ programming language.
Legacy
With over 70 different versions from Intel, AMD and Cyrix (not including those from IBM, SGS-Thomson, Texas Instruments and others), the 80486 will give the original 8086 a run for its money as the most iterated x86 CPU in history. Yet despite the drop-in clones and upgrades, the 80486 was nearing the end of its run when the Windows 95 revolution arrived, ensuring Intel rode the wave of success aboard its latter Pentium processors as Microsoft’s new operating system changed the way we viewed computers.
Yet, as the Pentium CPU took hold, Intel still found a ready market for its 386/486 cores in industrial applications, only stopping production on both in late 2007 and paving the road for today’s booming embedded processor market.
Nevertheless, despite the CPU families that have passed since, the 80486’s legacy – its bus multiplier, on-board cache and FPU – lives on today. So as we mark issue #486, we also pay tribute to one of the most iconic CPUs of the last 50 years. Nice work, 80486.