The (Almost) Definitive 486DX/50 Article

(Source: Infoworld, 25th May 1992, p56)

We need to start at the beginning, because understanding the timeline of the 486 - Intel's 4th generation x86 CPU - is key to understanding the story of the DX/50. (I also can't not start at the beginning, so "I'm sorry" or "you're welcome!" depending on how you feel about that.) This entire article is actually a complete accident. It was supposed to be the preface to the article I wanted to write, which was everything I found out from benchmarking and comparing a DX/50 against its closest competitors. I have, at least, made this a separate article, so you if you just want to look at the findings of my tests, you can go to the other one (once its completed I'll add the link). I'm not going to get massively technical here - look at the datasheet for that - but I will try to get as much information as possible in one place while clarifying dates and clearing up misconceptions, because there are a few.

The 486 Revolution

Intel initially finalised the specifications of their next gen 486 in June 1987¹, with a somewhat vague arrival date of 1990. Speculation about the chip continued for the next couple of years until Chicago's Comdex Spring in April of 1989, when Intel finally revealed the first samples of their new CPU, priced at $950 in quantities of 1,000². Actual systems including the 486 weren't expected until Q4 that year when production would begin in full, though IBM showed a prototype system at the end of April. The 486 was actually a pretty big leap ahead of its predecessor, despite few new instructions being added, thanks to some architectural enhancements. Through the use of a more precise 1 micron manufacturing process, Intel were able to integrate a co-processor into the die (most 386 systems did not ship with a co-processor²). It also used the RISC-inspired technique of pipelining, which allows a new instruction to be worked on before the previous one has completed - this was a step closer to the superscalar design of the future Pentium. The other significant enhancement was internal cache memory. Cache was introduced with the 386 and was external SRAM at this time. While it provided improved RAM access times, there was still some latency. By integrating 8K of cache onto the die of the CPU itself, access to the data and instructions stored there was instantaneous. This internal cache was also called 'level 1', while the external SRAM was called 'level 2'. Some early or cheap 486 systems didn't include this.

These enhancements meant a 486 was about twice as fast as a 386 running at the same clock speed.

(Source: Infoworld, 8th May 1989, p38)

The first 486 system to be announced was Apricot's VX FT server, as early as June, with the initial 25MHz model³. It's hard to imagine an DX/25 being at the heart of a high-end server today, but remember that this was the fastest x86 CPU in the world at the time. It wasn't all plain-sailing, however: the first teething troubles appeared as early as October that year, when it became apparent there were bugs in the FPU of the B4-stepping of the chip⁴. This delayed systems for at least a month, but this coincided nicely with Comdex Fall so everyone got to show their systems off anyway.

Volume shipping of the fixed 486 began in early December 1989⁵ and the first 33MHz systems began appearing in February '90, the month that a second bug was discovered in systems with the new EISA bus⁶. April then saw the release of the co-pro-less 20MHz 486SX and complementary 487 co-processor upgrade (technically a DX with a different pinout - Intel never made a discrete co-pro for the 486) and the first mention of their 50MHz model, said to be capable of 40 million instructions per second (MIPS)⁷. Considering that the DX/20 was capable of 20 MIPS, it's pretty impressive that Intel were planning to deliver double the power within a couple of years. By pricing the SX model at less than half the cost of the existing DX models, Intel was aggressive in its efforts to establish the 486 as the mainstream desktop CPU. This was somewhat ambitious, as most users around this were contemplating upgrading their 286 to a 386, and AMD were selling the best-value chips on that platform. For context, 386-based systems accounted for half of all PC unit sales in 1992, but by 1993 the 486 took over with 66% of sales so Intel's strategy ultimately worked⁸. What helped was that they had no competition at that time. Aside from a very specific agreement with Cyrix, Intel was, for the first time, not legally obliged to license its 486 designs to anyone else, as had been the case with the 8088, 80286 and 80386. This did land them with a number of antitrust lawsuits, however, which usually only arose when they tried to sue a competitor.

(Source: Computerworld)

50Mhz... But Not From Intel

Hilariously, the first 50MHz 486 showed up in October 1990, a full 8 months months before Intel even announced their official model⁹. In fact at least two cheeky companies - Velox and Cambion - sold peltier-based products that upped the voltage and cooled a DX/33 effectively enough that it could be overclocked to 50MHz¹⁰. I think this is one of the earliest extreme overclocking products I've ever heard of. There was talk that Intel might sue them considering that their product would be in direct competition with the real deal, but I don't think there was a huge amount of buyer confidence in running chips outside their spec. Certainly makes me wonder if the performance would match a genuine chip.

Business Only

Intel officially announced their 50MHz model at PC Expo in June 1991 (on the same day AMD announced their 25MHz 386SX clone!), and it was received with enthusiasm by some system builders and caution by others¹¹. With the Q4 arrival date some way off on the horizon, a few OEMs preferred to focus on selling the existing DX/33, while others had plans for multi-CPU systems. Intel also announced a custom cache module to optimise their newest CPU and help reduce 'design issues', though it's unclear how many manufacturers actually adopted it - cost was cited as a significant issue - and some manufacturers chose to design their own cache solution instead. It was clear from the off that this CPU was going to be used predominantly, if not exclusively, in servers and mainframe-class systems and there were two big reasons for this:

1. Cache: a 50MHz bus requires at least 20ns SRAM for its external cache, and this was pretty expensive in 1991. As an example, a slower 64KB of cache for a 25MHz system would set you back $150 in August of '91, and 256K was considered an optimal amount so that's $600 alone (the equivalent of $1,300 today). Goodness knows how much 20ns chips would be. By comparison, DRAM was $100 per megabyte at the time, so normal speed SRAM was 24 times the cost¹². Complementing components, such as video and I/O, would also need to be 'server grade' and that meant EISA, SCSI, etc. It wasn't so much of an issue to match the 50MHz bus speed because the local bus was in its infancy at this time, and didn't really mature until late 1993.
2. The FCC, at least in the US market. All computers produce electromagnetic emissions capable of causing interference and must be tested to conform to certain limitations before they can be authorised for sale. The two main categories for computers are class A (business) and class B (residential). Class B is much more stringent and, therefore, more costly to meet. System manufacturers anticipated that the 50MHz frequency of the DX would make it harder to meet class B, so they didn't bother wasting the time and money. This meant that it would not be authorised for sale to individuals, making it a de facto 'business only' CPU¹³.

Some desktop suppliers of the latest chip actually considered it to be 'too powerful', which definitely contributed to the general view that the DX/50 would be limited to only the most high-end business applications¹⁴. The speed bump wasn't the only improvement made in the 50MHz model. It also received a JTAG test access port (TAP) and although a reason for this isn't documented, it's likely it was so that manufacturers could test bus stability of their systems with the new CPU.

(Source: Infoworld)

Clock-Doubling on the Horizon

The DX/50's release was overshadowed somewhat by plans for a 66MHz model due to arrive in autumn the following year (plus talk of the next-gen P5¹³). This is actually the first time 'clock-doubling' is publicly mentioned by Intel, though it wasn't called that at the time - this new method of having an internal clock that was double the speed of the external clock was initially named the 'double clutch', 'dual clock' or 'clock doubler' depending on which magazine you were reading.

NCR, among others, had big plans for Intel's new CPU. Their 3600 system was designed with massively parallel processing in mind, to deal with 'large transaction processing operations' for big retail clients like K Mart. This computer used thirty two 486DX/33 CPUs along with the same number of multi-CPU cards, each with two to eight of the new 50MHz chips for up to 288 processors in total¹⁵. This was due for release in December '91 and was a scalable design, costing between $850,000 and $8,000,000. Obviously this wasn't going to be running Windows - a new flavour of UNIX was to be developed specifically for this system. NCR are the people that invented WiFi alongside AT&T, and were one of the earliest successful adopters of SCSI, amongst other industry-shaping innovations. If you only looked at the stories from publications focusing on desktop computing, you would think the DX/50 was a flop, but that was far from the truth. Unfortunately I've been unable to obtain historical sales figures for each 486 chip so I can't back this up with data - there is plenty of anecdotal evidence such as reviews and adverts.

Too Hot to Handle

In August '91, not long after volume production began, Intel had to cease production of the DX/50 because initial shipments were getting too hot and shutting systems down. This was attributed to Intel's existing suite of tests being inadequate when testing the 50MHz CPU¹⁶. It's pretty well known today that the DX/50 was the first 486 that really required a heatsink, not that Intel was telling anyone that - quite the opposite, in fact (can't find the reference right now). It's quite plausible that system builders simply weren't installing sufficient cooling, or indeed any. Either way, Intel and Dell, the only suppliers selling systems equipped with the chip at that time, said they would not be recalling systems and hadn't experienced complaints from their customers¹⁷.

1.0 Micron or 0.8 Micron?

I've seen multiple people saying that the first stepping of the DX/50 was manufactured using a 1.0 micron process and then moved to 0.8 micron because of overheating problems, but I've found no evidence whatsoever to support this. There is even a discussion over at CPU World about an engineering sample of the chip that was apparently the earliest example of a die-shrunk DX/50 but, again, no sources are given. Every available press article I've read, however, talks about the 0.8 micron process being a necessary factor in the speed increase, just like the additional metal layer it facilitates to reduce the vertical size of the die¹⁸. Changing the layer construction is a significant effort and isn't the kind of thing you casually do between steppings, as far as I know. Even the 486DX datasheet doesn't elaborate, only stating that the CHMOS IV and V processes were used in the making of the 25, 33 and 50MHz chips, but not which ones applied. It's possible that a 1.0 micron initial run of chips only made it into the hands of OEMs but if this did happen then it's likely that they were all recalled and destroyed. Intel themselves stated that there was "virtually no chance" that anyone would encounter one of these chips as a result¹⁹. These early samples also lacked the enamelled Intel logo. I would love to come across one of these, because one way to prove it definitively would be to compare an early chip with a later one and looking at the gold cap on the bottom of the CPU - a chip made with the 1.0 micron process will need a larger cap than one made using 0.8 micron. I have not yet found anyone who has made such a comparison so, for now, it's completely unproven that the DX/50's manufacturing process changed between steppings.

Left: a 1.0 micron DX/33. Right: a 0.8 micron DX/50.

Weirdly, one publication mentioned Intel demonstrating a 100MHz chip¹⁸. I know what you're thinking - they must mean a clock-doubled model, except they go on to talk about DX2s separately in the next paragraph, so they're either confused or Intel really did plan to go for a 100MHz front side bus. Such a thing seems absurd on so many levels, however. The same article suggested that a DX2/40 would be part of the future line-up and another mag speculated over the possibility of a DX2/100¹⁹.

DX2 & OverDrive

At least one supplier in Feb '92 said that Intel had effectively 'hit the wall' with the DX/50²⁰, just as mainstream systems had begun shipping. Vendors had also begun turning their attention to the OverDrive range of CPUs - due to be announced in March '92 - which would be a 'drop in' upgrade allowing users to increase the speed of their existing systems without having to change any of the other components. As an aside, system vendors did not like Intel selling CPUs directly to consumers if it meant those users were delaying the purchase of a new PC for a couple more years. Intel's CPUs were not retail parts and were usually only sold through OEMs as part of systems. The OverDrive range effectively marked Intel's entry into the retail sector and that may explain why there were so expensive - $699 for the DX2/50 when it was released and $549 for the 33 and 40MHz models. It was a strategy to deter most users from upgrading, while placating those that wanted to pay for more speed without spending thousands on a new PC. As such there aren't many around these days, relatively.

Just as the DX/50 was hitting its stride, the DX2 line was officially announced in March '92. Sold initially as an OEM part running at 50MHz internally²¹ (25MHz externally), the consumer OverDrive part was due to follow at a later date. System manufacturers loved it because they could ship existing systems unmodified with the new chip installed for a claimed 70% performance improvement and no FCC pain-in-the-ass²².

(Source: PC Mag, 15th Sep '92, p154)

To see how the DX/50s productions issues affected system vendors, we had to wait until June '92 for PC Magazine's group test of 19 of the first DX/50 machines. This featured systems that were shipping to customers by January that year, 7 months after the chip's initial announcement and 3 months after the 'good' DX/50 became available. The findings were positive: systems were 30% higher than the previous fastest 486, the DX/33, with a typical spec of 8MB RAM, a 300MB hard disk, SVGA graphics, plus DOS 5.0 & Windows 3.0. The DX/50's place as a server-grade CPU was confirmed - though it was claimed that the new DX2/50's raw performance was 'virtually identical'²³, its lack of I/O performance meant it was intended for the masses, and not seen as a threat to the DX. The linked article also provides a really good explanation of the technical challenges vendors faced in creating 50MHz systems, on page 116, and a look a the production process.

"Intel's step up from the 33MHz 486DX chip to a 50-MHz version required additional technical refinements. Both chips contain essentially the same processor logic, with a math coprocessor, an 8K memory cache, and 1.2 million transistors. In order to coax faster performance from the 486, the 50-MHz part uses a submicron (0.8 of a micron), three-layer chip design (versus the 33-MHz's 1 micron, 2-layer approach)." (p116)

PC Magazine's group test in September 1992, however, pitted the DX and DX2s against each other to provide a direct performance comparison²⁴.

"Just how important is an external, secondary processor cache? So important that PC Magazine Labs found DX2s with a well-designed 128K (or larger) cache run at 96 percent the processor performance level of a 50-MHz 486DX ... [T]he difference is almost unnoticeable if you're not performing memory-intensive tasks..." (p115)

"The average memory performance for all the DX2s was 6,314 kilobytes per second (compared with 8,017 KBps for the DX/50s)--78 percent of the performance of true 50-MHz systems ... Under most applications, PCs utilising the clock-doubler technology should perform nearly on the same level as a true 50-MHz 486 when the DX2 chip is used with an appropriately designed external cache." (p127)

(Source: Infoworld, 17th Sep '92, p32)

The Competition Heats Up

(It literally did - the DX2 ran a lot hotter than the DX). It seems that the writing was on the wall. Already it was obvious that the imminent 66MHz DX2 was likely to pose a threat once it arrived. Systems built around the DX2/66 began to show up in November, but it wasn't as clear cut as you would think. Infoworld's group test of 17 PCs shows why²⁵. Firstly, Intel Priced the DX2/66 $100 higher than the DX/50, so it wasn't a no-brainer. Secondly, they acknowledged a 9% performance increase over 50MHz systems but said:

"[S]ynchronising the timing between internal and external operations can be tricky. It's possible that some operations, particularly those that involve memory- or disk-intensive access, may actually be slower with the DX2/66 than with the DX/33." (p114)

Personally I think that's a bit of a bonkers thing for a tech rag to say, especially when they haven't actually provided any numbers to back it up. Tricky timing issues? May be slower? What they're probably referring to is wait states undermining the internal speed of the DX2, but it's almost as if Intel asked them to create a veil of uncertainty around this new 'too good to be true' CPU. Except no, because Intel themselves were publicly discounting the DX/50 back in August.²⁶

"[D]esktop users can expect to see a 30 percent improvement in performance ... when compared with Intel's true 50-MHz 486 processor ... the DX2/66 requires less engineering expertise and uses less costly components than a true 50-MHz-based system does ... many of the design issues that appeared with the 50-MHz system have now disappeared." (p32)

These were the words of Anand Chandrasekher, product marketing manager for the DX2/66, so either he was pissing off a lot of people at Intel who were behind the DX/50, or Intel had chosen to cut their losses and move on to this more reliable technology.

(Source: PC Mag, 26th Jan '93, p183)

Infoworld and others noticed that systems with at least 128K of cache would perform better than those with 64K or none. While it may be inconceivable 30 years later that OEMs were selling 486 systems with little or no level 2 cache, cost - or, rather, value - was a huge deal and if consumers didn't really understand or appreciate the relevance of cache, then they wouldn't consider it a worthy investment.

The biggest reason Infoworld could give for choosing a DX2/66 over a DX/50 was the price: the average 50MHz system was around $2,000 more. This is unsurprising as such systems were usually servers and would therefore be better-equipped, with features like more cache, SCSI, greater storage and caching drive controllers. They also cite local bus performance as a factor because the VESA local bus was brand new at the time and didn't support 50MHz operation yet, along with all the other proprietary local buses. The bottom line here is that there was very little emphasis on comparing the actual performance of Intel's top-end chips at this point, almost like they were apples and oranges.

The DX/50 Marches On

Moving forward to January 1993, PC Magazine conducted a massive test of 74 systems that showed the DX2/66 in its stride. Local bus graphics was still in its infancy, but system vendors had learned quickly how to get the most out of the new CPU²⁷. You would think that everyone was ready to dethrone the DX/50 by this point, but apparently not.

"[F]ast video performance not only makes PCs run faster, it makes them seem faster still. We've rarely seen that demonstrated so well as with these 66-MHz DX2s. While their average performance is only about 15 percent to 20 percent ahead of the 50-MHz 486DXs that were our previous speed champs--a margin of improvement that does not stir much interest in most PC users--the fast video subsystems of these machines often makes them appear far faster." (p122)

They've basically discounted a measurable performance improvement as... perceived? Insignificant? At this point I'm confused - surely most people would say that a 20% improvement had some merit? They seem to double down in their article on local bus video in the same issue, saying that "a local-bus 486DX/50 should outperform a local-bus 486DX2/66 because the clock-doubled DX2/66's local bus stops as 33MHz." Again, no numbers to back this up; lots of 'should' and 'may' being thrown around. Yet ask anyone today which system will perform better and the DX/50 will quickly be discounted for multiple reasons, despite very few people properly testing their systems from what I've seen (yes that's a dig). What about GUI performance? Hard drive transfers? There are many factors that can be compared.

Pentium Cometh

(Source: PC Mag, 11th May '93, p215)

In the meantime, on March 22 of '93, Intel unveiled their Pentium CPU and really put the cat amongst the pigeons²⁸. Competitors, such as IBM and Cyrix, had only just started to released their own 486 clones (under license from Intel) and suddenly (well, not suddenly - the P5 had been talked about since June '91, remember?) Intel had released their next-gen chip. At $900 in volume purchases, it was never going to threaten the healthy 486 market, but it did make the DX/50 Intel's 3rd-fastest chip behind the DX2/66.

PC Magazine did a group test of servers in May 1993, relatively late in the life of the DX/50, and found that "systems with 486DX/50 processors should have a performance advantage over 486DX2/66 systems in reading data from disk cache memory²⁹." These magazines really overuse the term 'should'. Anyway, of 9 servers tested, 3 were equipped with the DX/50, and the 'editor's choice', the Zenith Z-Server 450DE, was one of them, scoring 10 to 15 percent faster on the I/O throughput tests than its competitors. Not bad, all things considered.

In July 1993, the DX/50 reached its second birthday. PC Magazine ran an article on The Perfect PC and, to show how things had moved on in the last year, an entry-level system was considered to have a 486SX rather than a 386³⁰. They also labelled the DX2/66 as "the value choice for power users".

"In the hierarchy of computing, comparing a 50-MHz DX to a 66-MHz DX2 is problematic. The DX2 is better at processor-intensive tasks (calculation- and graphic-intensive programs); the plain DX is faster at memory intensive applications. Because 50-Mhz motherboards are difficult to design and manufacture, many PC makers have focused their attention on the 486DX2/66 and orphaned the 486DX/50." (Page 127)

It was true - Red Hill Technology shared their own experience of the DX/50: they only sold one but had to underclock it at 40MHz just to get it to run without issues³¹. Systems featuring the DX/50 were still being produced in December of 1993, according to PC Magazine's 486 buyers guide³², though out of 89 lines being produced by the various manufacturers, only 4 offered a DX/50 option, while 83 featured the DX2/66. Taking a look at the distribution of scores, the DX/50 put in a strong showing.

How the chips stack up (PC Magazine, 7th Dec 1993, p182)

Although it's no surprise that the sole Pentium system in the group murdered the competition, what's interesting is that, while the highest-performing DX2/66 scores about 47, the slowest only manages 27, producing an average of 39. The DX/50, meanwhile, is sitting happily at about 36 and therefore outperforming a fair number of 66MHz machines, and all of the DX2/50s. This just goes to show how important system design is in getting the most out of a CPU. Either way, it was clear that the DX/50 was on the outs, and the release of the clock-tripled DX4 only cemented it. Although not completely. A DX2/100 was actually rumoured around the time the DX4 (then called the DX3) was announced in July '93, which obviously would have had a 50MHz front side bus, and would have been intended to drop into systems that had been designed for the DX/50³³. Sadly nothing more was heard about this CPU, though the DX4 went on to successfully fill the gap between the DX2/66 and the Pentium.

So that's the full story. I think it's kind of sad that CPUs don't get a 'final day' when their manufacturer stops production, celebrates their achievements and sends them out to pasture. I think the DX/50 deserved such a send-off, but we will probably never know when the last one was produced.

As a celebration of its life, I want to discover, once and for all, where it outperformed its clock-doubled rival, where it didn't fare so well, and what the final score is. It will be a bit like what I did with the Tualatin vs Pentium 4 tests, except I'll be doing them myself rather than scraping them from other sources³⁴. It's worth noting, in the context of modern-day, retro benchmarking, that there were multiple versions of the DX2/66. The main model, the P24, originally had the 'write through' scheme on its internal cache, just like the DX. Late in 1994, however, the P24D was released, which used the faster 'write back' scheme. It's important, when benchmarking, to ensure you are comparing like-for-like. The P24D DX2/66 is going to wipe the floor with the DX/50 every time because it was not its contemporary - it was released over 3 years later³⁵.

Footnotes

The official model number of the DX/50 is A80486DX-50.

According to CPU World, there were 10 steppings of the 486DX/50: Q0209, Q302 and SXE69 are engineering samples and SX408, SX409, SX518, SX546, SX547, SX705, SX710 went into full production. These are displayed alphabetically, so it's often hard (or impossible) to work out where engineering samples fit in with the other versions chronologically. I have an SX518 and SX710 and both seem to behave very similarly. 

I have found at least two examples of people overclocking a DX/50 to 60 or 66MHz respectively with varying success and little detail. It makes sense for this to be possible given that the DX/50 was the first of the 0.8 micron CPUs, which should have theoretically given it some headroom - later CPUs on a particular manufacturing process historically have more trouble with higher frequencies (looks at the 1.13GHz Coppermine). It was an uncommon practice to overclock such a chip, though.

As ever, if you have enjoyed reading this, please consider buying me a coffee via Ko-Fi. I try my best to make sure that everything I write is historically accurate by citing primary sources and weaving together some kind of story from everything, but if you do think I've got something wrong, please comment below with a source and I'll be really happy to make corrections. I really enjoy writing about this stuff and it can be really time consuming! Also, I promise to give 20% of every donation to the Internet Archive, without which this article (and others I've written) wouldn't be possible. Thanks for reading :)

References

¹ Intel Finalizes Specifications for 80486 Chip (Infoworld, 15th June 1987, p.6)

² Hot New Chips (Infoworld, 8th May 1989, p.35)

³ Hold Onto Your Hat (And Your Wallet) (Byte Magazine, August 1989, p.8)

⁴ 486 Bugs Derail PC Vendors' Plans (Infoworld, 30th October 1989, p.1)

⁵ Intel Ships 80486 Chip in Volume (Infoworld, 4th December 1989, p.3)

⁶ Intel Identifies Bug in 486 Systems (Infoworld, 5th February 1990, p.21)

⁷ Intel Bids For High-End PC Market With Aggressively Priced 486SX (Infoworld, 29th April 1991, p.1)

⁸ U.S. Industrial Outlook 1994 (Department of Commerce, p.26-18)

⁹ Everex Set To Show 50-MHz PC (Computerworld, 8th October 1990, p.4)

¹⁰ Computers Hot Up With Cooler Chips (New Scientist, 29th June 1991)

¹¹ Intel Launches 50-MHz 486 at PC Expo (Infoworld, 1st July 1991, p.79)

¹² MIS Computer Systems Advert (Byte Magazine, September 1990, p.308)

¹³ Intel Sets Sights on 586 (Infoworld, 1st July 1991, p.1)

¹⁴ Fast 486s Too Much Too Soon (Computerworld, 3rd June 1991, p.1)

¹⁵ Users Wait for 3600 Reality (Computerworld, 17th June 1991, p.27)

¹⁶ Faulty Chip Test Suites... (Infoworld, 26th August 1991, p.1)

¹⁷ Chip Choice Outnumber User Needs (Computerworld, 26th August 1991, p.1)

¹⁸ The 50MHz 486 is Just One of Several... (PC Magazine, 24th September 1991, p.37)

¹⁹ 50-MHz 486-Based PCs (PC Magazine, 16th June 1992, p.116)

²⁰ Vendors Race to Support Intel's Clock-Doubling Dual-Speed Chips (Infoworld, 10th Feb 1992, p.1)

²¹ Clock-Doubler Blows Into Town (Infoworld, 9th March 1992, p.3)

²² Intel Rolls Out Its OverDrive Processor (Infoworld, 25th May 1992, p.27)

²³ 486/50: The New Performance Leader (PC Magazine, 16th June 1992, p.113)

²⁴ Intel Ups the Ante with Its 50-MHz DX2 (PC Magazine, 15th September 1992, p.111)

²⁵ 66-MHz 486DX2 Computers (Infoworld, 16th November 1992, p.114)

²⁶ Manufacturers Hop Aboard Intel's DX2/66 Bandwagon (Infoworld, 17th August 1992, p.32)

²⁷ DX2/66: The New Speed Limit (PC Magazine, 17th Jan 1993, p.111)

²⁰ Intel Launches Rocket in a Socket (Byte Magazine, May 1993, p.92)

²⁹ To Serve and Protect (PC Magazine, 11th May 1993, p.179)

²² The Perfect System (PC Magazine, July 1993, p.123)

³¹ The Red Hill CPU Guide: 386DX-40 and Competitors (The Red Hill Hardware Guide)

³² 486 Buyers Guide (PC Magazine, 7th December 1993, p.108)

³³ Faster 486 Could Overlap Pentium (Computerworld, 19th June 1993, p.1)

³⁴ The (Almost) Definitive Pentium III Tualatin Article (The Brassic Gamer Blog)

³⁵ Intel to Revamp DX2 With Faster Cache (Infoworld, 27th June 1994, p.1)

1995-12-04 Clock Multiplier (Google Patents)

1992-05-08 Clock Multiplication Circuit and Method (Google Patents)

1987-10-27 Computer Element Performance Enhancer (Google Patents)

1991-07-01 Intel Unveils 50-MHz Chip (Computerworld)

1991-06-17 Cold Shoulder (Computerworld)

1990-10-16 Pushing It To The Limit Dept. (PC Magazine)

1991-04-22 Cache's Motherboard, Icecap Module, Boost 33MHz CPU to 50MHz (Infoworld)

1990-11-05 Supercool Chip (Computerworld)

1991-08-05 Dual-Clock 486SX: Bonanza For Intel? (Computerworld)

1992-04-06 Cyrix gains customers for its 486 chip (Infoworld)

486DX Datasheet (DosDays)

History

2/1/23: First version published