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From: doug@terak.UUCP (Doug Pardee)
Newsgroups: net.micro.pc
Subject: Re: PC/AT fast xtal warning
Message-ID: <996@terak.UUCP>
Date: Fri, 17-Jan-86 14:59:27 EST
Article-I.D.: terak.996
Posted: Fri Jan 17 14:59:27 1986
Date-Received: Mon, 20-Jan-86 05:39:13 EST
References: <604@harvard.UUCP> <1101@ptsfa.UUCP>
Organization: Calcomp Display Products Division, Scottsdale, AZ, USA
Lines: 30

> In working through this and a few related problems, I picked up a lot of
> folk lore concerning the relative quality of various chips (i.e. Intel
> 8237s are good, AMD's are bad; Fujitsu 41256-15s are better than OKIs; ...)
> This folk lore did not discriminate between spec and pushed environments.
> Are there real [significant] differences?  I am a bit surprised, especially
> if true about licensed second source suppliers.

Yes indeed.  Sometimes the differences are "documented" in the spec
sheets.  I've encountered this with PALs (tm) -- one manufacturer specs
theirs as somewhat slower than MMI's "standard".  I've seen it with one
manufacturer's FAST (tm) logic: one part had much lower input loading
than Fairchild's "standard" part, making the input lines susceptible to
noise on a board where Fairchild's part worked fine.

Sometimes there are undocumented differences.  I've seen a problem with
a 10K ECL part obtained from a second source which didn't occur with the
Motorola MECL part.  The second sourced part had problems during initial
power-up, and wasn't reliable until each input changed state once.

Sometimes it's simply an ability to produce a faster part; AMD is a
second-source for the iAPX86 CPU's, but they seem to produce a given
speed part a few months before Intel does.

And DRAMs!  I'm beginning to think that no two DRAM chips are inter-
changeable, even from the same manufacturer   1/2 :-)    Aw, the spec
sheets are nearly identical, but their behavior is something else.

[Vision of Wendy's TV ad:  "What *kind* of parts?"  "Parts is parts."]
-- 
Doug Pardee -- CalComp -- {hardy,savax,seismo,decvax,ihnp4}!terak!doug