VOGONS

Search

Common searches

486 bug that was found in 1989?

Topic actions

First post, by demonized999

Posted on 
User metadata
Rank Newbie
Rank
Newbie

Hello guys!

Reading a magazine from 1990 i encountered a note which stroke me (cause I don't remember hearing about this one before) - apparently there was an 486 FPU bug found at some point in 1989 that forced the recall of some systems already assembled with it and even created delays for other vendors releasing their own 486 machines - specifically 486-25Mhz. The errata was discovered by Compaq and there were in fact two (!) bugs - first was able to be mitigated by workaround that Intel sent to vendors but the second one could be eliminated only by releasing a new revision of the chip.
It was said that after that point Intel changed the designation on the CPU from 486-25 to 486DX-25.

Anyone knows more about this? Anyone in possession of an affected processor? There is not much info about that I can find anywhere..
Starting to think that I found a "Mandela effect" 😁

Reply 2 of 4, by demonized999

Posted on 
User metadata
Rank Newbie
Rank
Newbie

Thanks!
Some information inside these comments!
Still I am amazed that this is not something discussed so often as the "infamous" FDIV bug and info is so rare and hard to obtain.

Reply 3 of 4, by Deunan

Posted on 
User metadata
Rank Oldbie
Rank
Oldbie
demonized999 wrote on 2023-03-11, 22:05:

Still I am amazed that this is not something discussed so often as the "infamous" FDIV bug and info is so rare and hard to obtain.

There's quite a few bugs in 286, 386 and 486 CPUs. Intel approach to those was alwasys "don't do that". They fixed what had to be fixed, bugs that could break userland programs. Everything else was to be worked around software side.
AFAIR the FDIV bug only got famous because Intel already shipped a number of these CPUs and was pretty much on-track to bury AMD then and there (as per ruling AMD could only copy 486 but nothing newer). So Intel put a lot of effort, and money, in ads and execution in general, only to be caught with their pants down. That being said, Pentium was a success once the 3.3V models appeared.

Reply 4 of 4, by Horun

Posted on 
User metadata
Rank l33t++
Rank
l33t++
Deunan wrote on 2023-03-11, 23:43:
demonized999 wrote on 2023-03-11, 22:05:

Still I am amazed that this is not something discussed so often as the "infamous" FDIV bug and info is so rare and hard to obtain.

There's quite a few bugs in 286, 386 and 486 CPUs. Intel approach to those was alwasys "don't do that". They fixed what had to be fixed, bugs that could break userland programs. Everything else was to be worked around software side.
AFAIR the FDIV bug only got famous because Intel already shipped a number of these CPUs and was pretty much on-track to bury AMD then and there (as per ruling AMD could only copy 486 but nothing newer). So Intel put a lot of effort, and money, in ads and execution in general, only to be caught with their pants down. That being said, Pentium was a success once the 3.3V models appeared.

Good point. OT but similar: There were many bugs in the 287 and 387 depending on which make/model you got. That is how the term "errata came to be iirc 😀

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Go to top of page Go to top of page
Back to General Old Hardware
Close window
Close window