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From: muth@amdahl.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Why 4.77MHz on clones?
Message-ID: <5426@amdahl.UUCP>
Date: Wed, 28-Jan-87 13:27:47 EST
Article-I.D.: amdahl.5426
Posted: Wed Jan 28 13:27:47 1987
Date-Received: Fri, 30-Jan-87 02:10:30 EST
References: <1292@ho95e.ATT.COM>
Distribution: na
Organization: Amdahl Corp, Sunnyvale CA
Lines: 13

In article <1292@ho95e.ATT.COM>, wcs@ho95e.ATT.COM (#Bill.Stewart) writes:
> A lot of PC clones offer two speeds, 4.77 and 7.x or 8.0 MHz, and claim
> the 4.77 is for compatibility.  What is the compatibility problem?
> Add-on hardware?  Stupid copy-protection?  Do I need to care?

Some software (mainly games) uses timing loops that are based on 4.77 MHz.
If you run these programs on machines with faster clocks (like a clone or
an AT) you end up with some real interesting results.

There may also be add-on hardware that counts on 4.77 MHz. I know of one
LAN adapter that works on AT's running at 6MHz, but not at 8MHz.
-- 
John A. Muth           ...!{ihnp4,hplabs,sun,nsc}!amdahl!muth