P2 CPU "class, " but 386/486 ISA "core" are commonplace -- AMD5x86 = 486 ISA

[Bryan J. Smith]

Per Bjornsson wrote:  
> Pentium = 586 obviously.

I like to refer to it as the Pentium ISA.  The "586" moniker can be
marketing-based.

> Also a 586:
> "The ÉlanSC520 microcontroller combines a 32-bit, low-voltage Am5x86
> CPU with a complete set of integrated peripherals..."

No. The AMD 5x86 is a 486 _ISA_.  The name "586" is _marketing_.

Understand that the AMD 5x86 _is_ the AMD 486 with some performance
tweaks (FSB, speed, cache, etc...).  It's a 486 _ISA_.

The AMD 5x86 _pre-dates_ the K5.  It was always debated if the K5 was
Pentium or 486 ISA.  It seemed thave some issues with some Pentium
instructions.

The K5 redesign, or those with more than a 120MHz "rating" -- wasn't
actual speed, were based on the 2nd generation NexGen Nx586 with FPU. 
The original NexGen Nx586 was a 4-issue i386 if you can believe that!
I believe these latter K5s were i486 ISA with most Pentium ISA
compatibility.
[ NexGen's RISC86 sub-ISA core is at the heart of all current AMD
processors ]

It actually wasn't until the AMD K6 that it was fully Pentium ISA
compatible.

Cyrix had the same issues.  Not only was the Cyrix 5x86 also only a 486
ISA, but the 6x86 through P200+ (150MHz) was _still_ a 486 ISA.

I don't think it was until the "L" version or the "M2" that Cyrix made
it to full Pentium ISA compliance.

> Basically I think that I'm more or less agreeing with you: Fedora
> shouldn't dump old ISAs unless there is a real, tangible gain; moving
> beyond 486 doesn't really seems to give us that. Where we differ is
> that I think that ignoring the 386 by explicitly using NPTL is a good
> idea and very much in line with the Fedora goals.

If NPTL require an 486 ISA, then a 486 ISA should be the standard, I'll
concede.  There are various segmenting/table paging issues that I
understand even the 386 MMU doesn't handle.


-- 
Bryan J. Smith, E.I. -- b.j.smith at ieee.org