Microcode, which is a no-go for modern designs

[Josh Dersch]

On Sun, Jan 6, 2019 at 10:59 AM Jeffrey S. Worley via cctalk <
cctalk at classiccmp.org> wrote:

> On Sat, 2019-01-05 at 12:00 -0600, cctalk-request at classiccmp.org wrote:
> > Re: Microcode, which is a no-go for modern designs
>
> I was a tech in the 90's when the original Pentium FDIV bug was
> storming.  The issue was confined to the integrated floating point
> portion of the processor and was therefore rarely an issue as the vast
> majority of software did not use the mathco portion of the chip.  Only
> a handful of applications and relative handful of users were affected.
> This became Intel's position on the matter and they hoped the issue
> would just die down to those handful whom they would provide new chips.
>
> The issue did not die down and the bad press forced the decision to
> replace ALL pentiums affected.  Only a relative few were actually
> replaced in the home and small business arena.  A software patch was a
> common solution to the problem.  It masssaged input to the FDIV
> instruction to produce a corrected result and worked pretty well as I
> recall.
>
> At the time of the storm, the Pentium was still pretty new and very
> expensive.  Most folks were getting along with AMD k5 and k6
> processors.  I WAS.  I went from k6 to Celeron.
>

That's a good trick, given that the K5 came out in 1996 and the K6 in 1997,
the FDIV issue blew up in late 1994.

- Josh



>
> Best
>
> Jeff
>
>