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Date:      13 Dec 2002 18:07:56 +1300
From:      James Pole <james.pole@paradise.net.nz>
To:        Charles Swiger <cswiger@mac.com>
Cc:        freebsd-stable@FreeBSD.ORG
Subject:   Re: Cyrix CPUs, was: Re: Repeatable crash from nautilus2
Message-ID:  <1039756076.12023.5.camel@localhost>
In-Reply-To: <004901c2a25c$0c381c50$0301a8c0@prime>
References:  <20021213021012.61714.qmail@web40303.mail.yahoo.com> <004901c2a25c$0c381c50$0301a8c0@prime>

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On Fri, 2002-12-13 at 16:58, Charles Swiger wrote:
> Rhett Monteg Hollander wrote:
> [ ... ]
> > What Cyrix CPU? And what OS'es? And maybe vice versa?
> > I do remember hard issues with WinNT 3.51 and original
> > Win'95 when running on Cyrix 5x86\6x86 or NexGen
> > Nx586.
> 
> # CPU_BTB_EN enables branch target buffer on Cyrix 5x86 (NOTE 1).
> #
> # CPU_DIRECT_MAPPED_CACHE sets L1 cache of Cyrix 486DLC CPU in direct
> # mapped mode.  Default is 2-way set associative mode.
> #
> # CPU_CYRIX_NO_LOCK enables weak locking for the entire address space
> # of Cyrix 6x86 and 6x86MX CPUs by setting the NO_LOCK bit of CCR1.
> # Otherwise, the NO_LOCK bit of CCR1 is cleared.  (NOTE 3)
> [ ... ]
> # NOTE 1: The options, CPU_BTB_EN, CPU_LOOP_EN, CPU_IORT,
> # CPU_LOOP_EN and CPU_RSTK_EN should not be used because of CPU bugs.
> # These options may crash your system.
> #
> # NOTE 2: If CYRIX_CACHE_REALLY_WORKS is not set, CPU cache is enabled
> # in write-through mode when revision < 2.7.  If revision of Cyrix
> # 6x86 >= 2.7, CPU cache is always enabled in write-back mode.
> #
> # NOTE 3: This option may cause failures for software that requires
> # locked cycles in order to operate correctly.
> 
> Yum.  Sounds tasty.

Indeed it does. Intel and AMD, despite having produced processors for
many years, still havn't achieved the "fame" that Cyrix has achieved in
the LINT file.

I think the fact Cyrix isn't very popular these days, compared to
Intel/AMD processors says a lot about the quality of their processors
back in the Pentium/586 days. Nowdays people use Intel/AMD processors
and to date I havn't come across any serious problems with those
processors.

I'm not saying they don't have problems, but Intel/AMD are often willing
to replace CPUs with bugs (such as that floating point pug that occured
in the Intel Pentium in the mid-1990's) and many of the bugs are so
simple they are solved by a simple software workaround (eg Intel's F00F
bug -- almost every OS including FreeBSD includes the workaround).

- James


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