Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!tut.cis.ohio-state.edu!bloom-beacon!bu-cs!dartvax!eleazar.dartmouth.edu!stevel
From: stevel@eleazar.dartmouth.edu (Steve Ligett)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Speeding up old PC's
Message-ID: <10358@dartvax.Dartmouth.EDU>
Date: 11 Oct 88 15:24:50 GMT
References: <3009@dalcs.UUCP> <16800379@clio> <3850@encore.UUCP>
Sender: news@dartvax.Dartmouth.EDU
Reply-To: stevel@eleazar.dartmouth.edu (Steve Ligett)
Organization: Dartmouth College, Hanover, NH
Lines: 35

There was discussion of how fast the ram chips have to be for a PC.  Including:

In article <3850@encore.UUCP> corbin@pinocchio.UUCP (Steve Corbin) writes:
>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.

>	It takes 4 clocks ticks for a bus cycle on the 8086/8088.
...
then many important lines that I've had to delete to get to the answer:

> 435ns.
>
>Depending upon how adversely the design of the control path affects the
>access time, it is entirely possible that 400ns rams will work.

Here, let me try to fool inews into thinking I wrote Stephen's disclaimer:

Disclaimer:  The real answer can be found by a detailed timing analysis
of the actual design which is far from what I did.

>Stephen Corbin	    UUCP:	{bu-cs,decvax,necntc,talcott}!encore!corbin

Yes, that is correct as far as it goes.  A look at the schematics reveals
that there's 2 ls245s in the path, and well as the address mux circuit.
The timing for the RAS and CAS isn't optimized for the circuit (just
off-the-shelf parts).  I didn't look at the parity checking.  So, I'd be
willing to believe (without a more detailed analysis) that 300 ns rams
might work, and I'm pretty sure that the 250 ns ones in my PC work.

Argh, now to try to trim this article down so that I can send it.  (later
... I hope that does it, I've butchered the other articles.)  Forgive me
Mike and Stephen.
   Steve Ligett     steve.ligett@dartmouth.edu or
(decvax harvard ihnp4 linus)!dartvax!steve.ligett