5 ms·

My father wanted a computer for doing CAD, so of course he needed a 387 beside the 386. From what I remember, unlike the 386, for which both Intel and AMD mode

My father wanted a computer for doing CAD, so of course he needed a 387 beside the 386. From what I remember, unlike the 386, for which both Intel and AMD models were available, the 387 was produced only by Intel, which meant that the cheaper and more performant 40MHz AMD processor had not a corresponding FPU, so if you needed floating point operations you had to spend more money for a slower CPU. What he ended up doing instead, was to get a relative to assemble him a PC with a 40MHz AMD 386 and a 20MHz Intel 387. Surprisingly it did work, as long as one would remember to press the "Turbo" button to slow the 386 to 20MHz before using the CAD software otherwise it would crash. The rest of the software would happily work at 40MHz

deleted 3y ago
[deleted]
Narishma 3y ago
IIRC you could have a 386 with a 287 co-processor.
- scruffyherder 3y ago
  Yeah, although it was apparently really early 386 boards. I’m not sure how it would work electronically though.
  - bombcar 3y ago
    Iirc the FPU was basically a second processor that the first would send data to and get an interrupt when it was done (or similar).
oaktowner 3y ago
OMG I had forgotten all about the "Turbo" button. Great story, and thanks for the trip down memory lane.
- enobrev 3y ago
  I remember them well enough. But this is the first time I've ever heard of an actual use for it.
  - plasticchris 3y ago
    It was useful for some old games where the frame rate was tied to the cpu frequency.
ChrisClark 3y ago
That's interesting. I specifically remember buying a math coprocessor for my AMD 386DX-40. My motherboard definitely had the slot for a dedicated co-processor though, maybe that was the difference.
- mrighele 3y ago
  I was a kid listening to "grown-up talking" so I could remember the wrong reason for the funny pairing, or maybe I'm getting old :-) (it's been 30+ years). English Wikipedia isn't very helpful on the regard but I found a page in German [1] that lists a number of 387DX-compatible chips running at 40MHz, so maybe it was just a matter of price, local availability, or lack of trust in the brands. [1] https://de.wikipedia.org/wiki/Liste_der_x86er-Koprozessoren https://de.wikipedia.org/wiki/Liste_der_x86er-Koprozessoren
- yuhong 3y ago
  AFAIK while AMD didn't produce the 387 there was alternatives from for example Cyrix and IIT at the time.
  - lproven 3y ago
    And the socket-compatible, better-than-the-original Weitek 3167. http://www.weitek.com/textual/products/wtl3167.html http://www.weitek.com/textual/products/wtl3167.html
NiloCK 3y ago
Low value comment, but I'm astounded some 30 years later to learn there's such a thing as a 387 processor. ... one more!
- ngcc_hk 3y ago
  It is a different game to play according to crossing the chasm. There were 8087, 80187, 80287 and 80387 is the last one. I do not know that only intel has 387 though.
takinola 3y ago
IIRC, the 386 and 387 were exactly the same chip. The difference between them being the 387 had an activated math processor while the 386 did not. If you plugged in a 387, it would disable the 386 chip and take over all the work of computation. Apparently, happened because the math coprocessor was where most of the manufacturing errors occurred so Intel just sold the defective chips as 386s in order to increase throughput
- KayEss 3y ago
  I think you're thinking of upgrading the 486sx which didn't have the on die coprocessor. That did disable the old chip as you basically replaced it with a 486dx
  - lproven 3y ago
    You're close but not quite. See above.
- lproven 3y ago
  You're wrong, and so is the first comment. Sorry (and to @KayEss). You're thinking of the 486. The 80386DX was the first x86 CPU to be 32-bit and have an on-chip MMU. And nothing else: no cache, no FPU. The FPU was a discrete part, the 80387DX. Because OS/2 1.x didn't support the 80386, and so couldn't run DOS apps well, and so flopped, the 16-bit 80286 kept selling well. It ran DOS fast and it could run Windows 2/286 and Windows 3 in Standard Mode which was good enough. It could only address 16MB of RAM but that was fantastically expensive and it was more than enough for DOS and Windows 3. So, because DOS still ruled, Intel made a cost-reduced version of the 80386DX, the 80386SX. This had a 16-bit data bus, so it could use cheaper 16-bit motherboards and 16-bit wide RAM, still limited to a max of 16MB. Still enough. That needed a maths copro for hardware floating point, too: a different part, the 80387SX. Then Windows 3 came along, which was also good enough, and started a move in PC apps to GUIs. Windows 3.1 (1992) was better still. So Intel had a 2nd go at the 32-bit chip market with the 80486, marketed as the "486". This integrated a better 386DX-compatible CPU core with a few extra instructions, complete with MMU, plus a 387-style FPU, plus a small amount of L1 cache, all onto one die. But it was expensive, and didn't sell well. Also, all the 3rd party x86 makers leapt on the bandwagon and integrated the extra instructions into 16-bit bus 386SX compatible chips and branded them as 486s: the Cyrix and IBM "486slc" for instance. This ate into sales of the real 486. So Intel came up with an ethically very dodgy borderline scam: it shipped 486s with the FPU disabled, calling them the "486DX" to reuse the branding that distinguished the 32-bit-bus models of 386 from the 16-bit-bus. People don't understand stuff like bus widths or part numbers, as your post demonstrates, and I mean no offense. They don't. So now there was a new model of 486, the 486SX with a disabled FPU, and the 486DX with it still turned on. The "SX" model needed a new motherboard with a 2nd CPU socket that accepted a "floating point co-processor", called the "487", which was nothing of the kind. The "SX" was a lie and so was the "487 copro". The 487 was a 2nd complete 486 chip that disabled the original and took over. But it reused the older branding, which is what you've remembered. Later, briefly, Intel made a cheaper cost-reduced 486SX with a smaller die with no FPU present, but not many of them. The clock-doubled 486DX2 took over quite quickly and killed the 486DX and 486SX market. Some commentators speculated that the 486DX vs 486SX marketing thing allowed Intel to sell defective 486s in which the FPU didn't work but if it did that was a tiny tiny number: a rounding error.

deleted 3y ago

[deleted]

Narishma 3y ago

IIRC you could have a 386 with a 287 co-processor.

scruffyherder 3y ago
Yeah, although it was apparently really early 386 boards. I’m not sure how it would work electronically though.
- bombcar 3y ago
  Iirc the FPU was basically a second processor that the first would send data to and get an interrupt when it was done (or similar).

oaktowner 3y ago

OMG I had forgotten all about the "Turbo" button. Great story, and thanks for the trip down memory lane.

enobrev 3y ago
I remember them well enough. But this is the first time I've ever heard of an actual use for it.
- plasticchris 3y ago
  It was useful for some old games where the frame rate was tied to the cpu frequency.

ChrisClark 3y ago

That's interesting. I specifically remember buying a math coprocessor for my AMD 386DX-40. My motherboard definitely had the slot for a dedicated co-processor though, maybe that was the difference.

mrighele 3y ago
I was a kid listening to "grown-up talking" so I could remember the wrong reason for the funny pairing, or maybe I'm getting old :-) (it's been 30+ years). English Wikipedia isn't very helpful on the regard but I found a page in German [1] that lists a number of 387DX-compatible chips running at 40MHz, so maybe it was just a matter of price, local availability, or lack of trust in the brands. [1] https://de.wikipedia.org/wiki/Liste_der_x86er-Koprozessoren https://de.wikipedia.org/wiki/Liste_der_x86er-Koprozessoren
yuhong 3y ago
AFAIK while AMD didn't produce the 387 there was alternatives from for example Cyrix and IIT at the time.
- lproven 3y ago
  And the socket-compatible, better-than-the-original Weitek 3167. http://www.weitek.com/textual/products/wtl3167.html http://www.weitek.com/textual/products/wtl3167.html

NiloCK 3y ago

Low value comment, but I'm astounded some 30 years later to learn there's such a thing as a 387 processor. ... one more!

ngcc_hk 3y ago
It is a different game to play according to crossing the chasm. There were 8087, 80187, 80287 and 80387 is the last one. I do not know that only intel has 387 though.

takinola 3y ago

IIRC, the 386 and 387 were exactly the same chip. The difference between them being the 387 had an activated math processor while the 386 did not. If you plugged in a 387, it would disable the 386 chip and take over all the work of computation. Apparently, happened because the math coprocessor was where most of the manufacturing errors occurred so Intel just sold the defective chips as 386s in order to increase throughput

KayEss 3y ago
I think you're thinking of upgrading the 486sx which didn't have the on die coprocessor. That did disable the old chip as you basically replaced it with a 486dx
- lproven 3y ago
  You're close but not quite. See above.
lproven 3y ago
You're wrong, and so is the first comment. Sorry (and to @KayEss). You're thinking of the 486. The 80386DX was the first x86 CPU to be 32-bit and have an on-chip MMU. And nothing else: no cache, no FPU. The FPU was a discrete part, the 80387DX. Because OS/2 1.x didn't support the 80386, and so couldn't run DOS apps well, and so flopped, the 16-bit 80286 kept selling well. It ran DOS fast and it could run Windows 2/286 and Windows 3 in Standard Mode which was good enough. It could only address 16MB of RAM but that was fantastically expensive and it was more than enough for DOS and Windows 3. So, because DOS still ruled, Intel made a cost-reduced version of the 80386DX, the 80386SX. This had a 16-bit data bus, so it could use cheaper 16-bit motherboards and 16-bit wide RAM, still limited to a max of 16MB. Still enough. That needed a maths copro for hardware floating point, too: a different part, the 80387SX. Then Windows 3 came along, which was also good enough, and started a move in PC apps to GUIs. Windows 3.1 (1992) was better still. So Intel had a 2nd go at the 32-bit chip market with the 80486, marketed as the "486". This integrated a better 386DX-compatible CPU core with a few extra instructions, complete with MMU, plus a 387-style FPU, plus a small amount of L1 cache, all onto one die. But it was expensive, and didn't sell well. Also, all the 3rd party x86 makers leapt on the bandwagon and integrated the extra instructions into 16-bit bus 386SX compatible chips and branded them as 486s: the Cyrix and IBM "486slc" for instance. This ate into sales of the real 486. So Intel came up with an ethically very dodgy borderline scam: it shipped 486s with the FPU disabled, calling them the "486DX" to reuse the branding that distinguished the 32-bit-bus models of 386 from the 16-bit-bus. People don't understand stuff like bus widths or part numbers, as your post demonstrates, and I mean no offense. They don't. So now there was a new model of 486, the 486SX with a disabled FPU, and the 486DX with it still turned on. The "SX" model needed a new motherboard with a 2nd CPU socket that accepted a "floating point co-processor", called the "487", which was nothing of the kind. The "SX" was a lie and so was the "487 copro". The 487 was a 2nd complete 486 chip that disabled the original and took over. But it reused the older branding, which is what you've remembered. Later, briefly, Intel made a cheaper cost-reduced 486SX with a smaller die with no FPU present, but not many of them. The clock-doubled 486DX2 took over quite quickly and killed the 486DX and 486SX market. Some commentators speculated that the 486DX vs 486SX marketing thing allowed Intel to sell defective 486s in which the FPU didn't work but if it did that was a tiny tiny number: a rounding error.