>
> Weren't the original 486SX'es just recycled early-stepping 486DX'es that had
> FPU bugs?
Every time this is brought up in comp.arch, it is widely shot down by
people who seem to know a lot about this kind of thing. The points
they generally make are:
* Faults in chips generally involve things like shorts from power to
ground, or miss-alignment over large areas. These kind of problems
will cause the entire chip to be unreliable, especially over the
long term life of the chip. It just isn't worth your reputation to
release chips that fail after a few months/years.
* Without doing some major redesigning of the chips, it isn't easy
(read cheap) to disable a portion of a chip after it is has been
made and completely tested. So, shipping working 486DX's as 486SX's
isn't profitable, and if you are going to redesign the chip, why not
redesign it with out the FPU?
* Major cost savings can be had by reducing the chip size, which
removing the FPU would do. Major cost savings can also be had by
reducing the amount of time it takes to test a chip to make sure it
completely works. Removing the FPU does this also.
There may have been a few 486SX's that were carefully modified 486DX's
for prototype purposes, but it is unlikely that any of them made it out
Intel, and if they did, they went to a very small set of key vendors.
Hardware is different than software. It is often very easy to disable
large portions of your software and ship of nearly identical bits to
customers for radically different prices. You can sometimes find
examples of this in hardware too, but probably not in things like
single chips like CPUs are.
-wayne
-- Wayne Schlitt can not assert the truth of all statements in this article and still be consistent.- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/