Path: utzoo!attcan!uunet!fernwood!apple!marc
From: marc@Apple.COM (Mark Dawson)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Does the new parity bit cause SIMM incompatibilities?
Message-ID: <39448@apple.Apple.COM>
Date: 13 Mar 90 14:01:34 GMT
References: <1990Mar13.045701.29647@athena.mit.edu> <22978@pasteur.Berkeley.EDU>
Distribution: na
Organization: Apple Computer Inc, Cupertino, CA
Lines: 36

In article <22978@pasteur.Berkeley.EDU> mkao@cory.Berkeley.EDU.UUCP (Mike "Butterball" Kao) writes:
>
>I learned from my digital design professor that the newest Macs (beginning
>witht he IIci I think) have added a parity bit to each byte, now resulting
>in 9-bit bytes. I suppose this means that these Macs use 9-bit SIMM's?
>
>I want to know because I currently own a Mac II with 4 MB and am considering
>buying 4 more MB to bring my machine up to the max; however, I am concerned
>that, should I decide to upgrade to one of these newer Macs, all my SIMM's
>will be useless. Is this true? 

NO!  There are two types of IIcis--parity and non-parity (I'm not sure if the
parity ones are shipping yet).  If you put parity SIMMs in the non-parity 
IIcis, you've only wasted your money getting more expensive SIMMs--you won't
get parity, nor will there be any hardware penalty (you will have the $$ 
penalty).  If you put non-parity SIMMs in a PARITY IIci, you'll only have
wasted the extra cost of the parity machine--you won't have parity.  In the
IIci w/parity, ALL of the SIMMs must be parity SIMMs for parity to be enabled.
(if you have a parity IIci && don't have parity SIMMs installed, you'll get
an alert box everytime you boot telling you that parity has been DISabled--just
press "continue" to go on with the boot).

In other (shorter) words, non-parity (8bit) SIMMs will work on all IIcis and so
will parity (9 bit) SIMMs.  Unless you have a burning desire (and extra $$)for 
parity, I'd suggest you just get fast (80ns fast-page mode SIMMs--though these
seem to becomming "regular" speed) SIMMs when you upgrade.

Mark

-- 
---------------------------------
Mark Dawson                Service Diagnostic Engineering
AppleLink: Dawson.M

Apple says what it says; I say what I say.  We're different
---------------------------------