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Today, we've decided to revisit some of the worst CPUs ever built. To make it on to this list, a CPU needed to be fundamentally broken, as opposed to simply being poorly positioned or slower than expected. The annals of history are already stuffed with mediocre products that didn't quite meet expectations but weren't truly bad.
Note: Plenty of people will bring up the Pentium FDIV bug here, but the reason we didn't include it is simple: Despite being an enormous marketing failure for Intel and a huge expense, the actual bug was tiny. It impacted no one who wasn't already doing scientific computing and the scale and scope of the problem in technical terms was never estimated to be much of anything. The incident is recalled today more for the disastrous way Intel handled it than for any overarching problem in the Pentium micro-architecture.
We also include a few dishonourable mentions. These chips may not be the worst of the worst, but they ran into serious problems or failed to address key market segments. With that, here's our list of the worst CPUs ever made.
- Intel Itanium
- Intel Pentium 4 (Prescott)
- AMD Bulldozer
- Cyrix 6×86
- Cyrix MediaGX
- Texas Instruments TMS9900
Which CPUs make up your list of Worst CPUs Ever Made?
(Score: 5, Informative) by bzipitidoo on Thursday April 23 2020, @01:37PM (6 children)
I'd rate Intel's 386SX and 486SX as pretty bad. They were lobotimized versions of the 386DX and 486DX, for purposes of filling a perceived low end market niche.
With the 486DX, Intel finally got rid of another of their marketing ploys, the splitting out of the floating point math, in order to sell that separately for a whole lot more money, 8087 to go with the 8086, 80287 to go with the 80286. etc. Only, almost no one bought them. You could get a little emulator software package, good enough to fool AutoCAD which refused to run if there was no math coprocessor. Yeah, emulating an 8087 on an 8086 was about 1/50th the speed, but it saved you over $500. I remember there was a one week period in which the price of the 80387 collapsed. Started the week at $600 (with the Cyrix 387 going for $500), and ended the week at $200, and they still weren't worth buying. Everyone knew the 486 was coming soon. Then what does Intel do? Try one more time to extort people for floating point math in hardware, by removing it from the 486DX and calling that a 486SX. You could add that back in by buying an 80387.
The 386SX was a different cut. No 386 had floating point math. They all needed a 387 for that. Instead, one of the selling points of the 386 was full 32bit -- in the 386DX. The 386SX backtracked on that. Still had all the 32bit functionality, but the bus was only 16bit. The SX alternated between sending out the low and the high half of a word in order to squeeze 32bit addresses and memory fetches onto that 16bit bus. That's what the 386SX was, a 386DX running at half the speed whenever any use of the bus was needed.
(Score: 3, Interesting) by RS3 on Thursday April 23 2020, @04:22PM (2 children)
My first '386 board came with a 287. It surprised me at the time- I thought it had to be a 387 to go with a 386, but evidently 287 is bus compatible.
Q: was the 386SX pretty much bus compatible with 286 glue logic? IE, could you pretty much drop a 386SX into a 286 MB design?
(Score: 0) by Anonymous Coward on Friday April 24 2020, @06:53PM (1 child)
The entire point of the 386SX, unlike the later 486SX was that it was bus compatible with the 286, allowing the clone box manufacturers to reuse existing 286 chipset designs with the 386 processor.
I know this because I have a 1989 Gateway 2000 386SX/16 sitting above me in storage. The motherboard got swapped out over the years, but as originally sold it had a 250W industrial power supply with a giant mechanical switch out the side. A full height (10.5"?) 60 megabyte MFM hard disk with a paper bad sector list in a pouch atop it, 4 megabytes of ram on either 2x2MB or 4x1MB SIMMs (had either 4 or 8 simm sockets, I forget which.) with a full length MFM/SERIAL/Parallel I/O card and a I think half length (only reached to the end of the motherboard, not the full length guides on the inner front face of the case.) The video card was an ATI VGA/EGA Combo card, maybe a Wonder? It had no audio onboard except the old style PC speaker which could do some really low fidelity mono-channel modulated sound, but usually was only used for different tones of beep. No Sound card. I eventually got a Thunderboard (8 bit Sound Blaster Clone) which netted me a game port, and later some secondhand ethernet cards for it. Managed to run windows 3.11 and later WFW 3.11 on it. Played Space Quest III and then IV (barely, got a 486 around that time that most of that game was played on.) all kinds of shareware games, my first internal 2400 baud modem, and a variety of other fun stuff after.
The soldered on-board battery eventually died on it and after jumpering it to get the system to boot I think the RTC blew up. Either that or when I tried to swap the memory back I used the wrong speed simms. One of these days I will examine it and see if I can get it booting again. For the record that 250W power supply still runs good and hard, but I have had more compact cases to use in the years since. That original was about the footprint of a 26-32" TV and took up most of a wide desk or table. But it was heavy enough to handle a large monitor set atop it :)
(Score: 2) by RS3 on Saturday April 25 2020, @02:07AM
Soldered-on battery one of those 3-cell shrink-wrapped ones? If so, likely a NiCad and might be leaking. If so, it's usually fairly easily cleaned. I use warm water, dish detergent, and an old toothbrush. Dry it well of course. There may be a connector for an external battery. RTC might be fairly easily replaced.
(Score: 2, Informative) by Anonymous Coward on Thursday April 23 2020, @04:25PM (1 child)
Not quite... you could not use the 80387 with the 486SX... you had to buy an "80487SX" which was literally just a full-featured 486DX chip packaged with an extra pin to prevent it from fitting in the same sockets.
When you added the 487SX the original 486SX is simply disabled and all processing is done on the "co-processor".
To be fair to Intel they almost certainly had a run of bad FPUs and this seems like a reasonably clever way to market the broken chips instead of scrapping them (just need to design the "upgradable" motherboard -- back in the early 90s this was probably not a huge ask because motherboards were fairly simple designs at the time). Obviously this proved to be fairly successful because they respun the 486SX several times (the later tapeouts would have the FPU removed instead of broken).
(Score: 2) by toddestan on Friday April 24 2020, @12:07AM
There was even a 486SX2, which was exactly what it sounded like - a 486DX2 with the FPU removed. I'm not sure if they were actually 486DX2's with a bad/disabled FPU, or they never had a FPU from the start. They were pretty rare, and I only remember seeing them in low end OEM systems like Packard Bell, possibly suggesting that they were actually 486DX2's with bad FPU's, and their rarity coming from Intel getting better yields later in the 486's run. As far as I'm aware there was never a 486SX4.
(Score: 2) by TheRaven on Friday April 24 2020, @03:38PM
The 386SX was lobotomised so that it could work with cheaper motherboards. It had a 16-bit external bus, significantly reducing the cost of motherboards and a bunch of other on-board peripherals.
The 486SX was intended to help with yields. Intel's 486 yields were quite low. Any that had broken FPUs could be sold as 486SX chips, any with working FPUs but broken 486 cores could be sold as 487s. As the yields increased, 486SX and 487 parts ended up just having the other parts disabled. The later 487s were actually 486DXs that took over from the original 486SX entirely.
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