Path: utzoo!attcan!uunet!husc6!bloom-beacon!think!ames!ncar!gatech!udel!rochester!pt.cs.cmu.edu!b.gp.cs.cmu.edu!Ralf.Brown@B.GP.CS.CMU.EDU
From: Ralf.Brown@B.GP.CS.CMU.EDU
Newsgroups: comp.sys.ibm.pc
Subject: Re: Speeding up old PC's
Message-ID: <234e0a42@ralf>
Date: 8 Oct 88 13:29:54 GMT
Sender: netnews@pt.cs.cmu.edu
Lines: 27
In-Reply-To: <16800379@clio>

In article <16800379@clio>, berger@clio.las.uiuc.edu writes:
}No - but I think that person is mistaken.  I'd like to see how he
}calculates that 400 ns rams should be sufficiently fast.

Here we go again.... (I think this should go in news.announce.newusers as a
"commonly asked question"....)

Rule-of-Thumb memory speed: (many memory chips actually perform better)

        max_access_time_ns = (1000 / clock_speed_MHz) * clocks_per_access / 2

where clocks_per_access is FOUR for 808[68] and TWO plus wait states for
80[23]86 machines.

So, the calculation for an original PC goes:

        1000/4.77 * 4 / 2 = 210 * 4 / 2 = 420ns

and for a 10/1 AT

        1000/10 * 3 / 2 = 100 * 3 / 2 = 150ns

--
UUCP: {ucbvax,harvard}!cs.cmu.edu!ralf -=-=-=- Voice: (412) 268-3053 (school)
ARPA: ralf@cs.cmu.edu  BIT: ralf%cs.cmu.edu@CMUCCVMA  FIDO: Ralf Brown 1:129/31
Disclaimer? I     |Ducharm's Axiom:  If you view your problem closely enough
claimed something?|   you will recognize yourself as part of the problem.