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From: info-mac@uw-beaver
Newsgroups: fa.info-mac
Subject: Re:  512k upgrade
Message-ID: <758@uw-beaver>
Date: Tue, 5-Feb-85 05:20:21 EST
Article-I.D.: uw-beave.758
Posted: Tue Feb  5 05:20:21 1985
Date-Received: Thu, 7-Feb-85 03:28:04 EST
Sender: daemon@uw-beaver
Organization: U of Washington Computer Science
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From: nate@cadmus (Nate Goldschag)

Eric-
	It is real hard for me to put the file on the net for various
reasons.  I sent a floppy with both files to Rich Cower so perhaps
he can put them on the net.
	150 ns memory chips refer to the access time from the RAS
signal on the chip - the time after RAS when read data is available.
So naturally 150ns chips are faster than 200ns chips and therefore
certainly OK for an upgrade.  Cycle time is something else.  A
150ns chip can access in 150ns but there will be a time when RAS
must precharge of perhaps 90 or 100 ns.  So the fastest you can cycle
a 150ns chip is about 240ns.  Don't confuse that 4 Mhz cycle rate
with the 8 Mhz 68000.  The 68000 with no wait states takes 4 clock
cycles to do a memory access so an 8 Mhz part has 500 ns to cycle -
plenty of time.