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From: johne@hpvcla.HP.COM (John Eaton)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Speeding up old PC's
Message-ID: <4740024@hpvcla.HP.COM>
Date: 10 Oct 88 15:52:03 GMT
Article-I.D.: hpvcla.4740024
References: <3009@dalcs.UUCP>
Organization: Hewlett Packard, Vancouver, WA
Lines: 15

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< No - but I think that person is mistaken.  I'd like to see how he
< calculates that 400 ns rams should be sufficiently fast.
----------
Very simple. The 8088 and 8086 each take four clock cycles per memory access.
At 4.77 Mhz thats 210 ns per clock or 840 ns for a complete cycle. The Address
out is valid 110 ns after the start of T1 and the Data is required 30 ns 
before the end of the third. That gives you 490 ns to go through the address
multiplexers, ram access and data buffers. If you drop in a 8 mhz part that
goes up to 550 ns. I forget the exact tap values used in the IBM memory 
control circuit but I believe that it was fast enough to support 400 ns ram.


John Eaton
!hpvcla!johne