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From: revatt@aluxz.UUCP (EVATT)
Newsgroups: net.micro.pc
Subject: Re: Weirdness in the PCjr - faster than normal 'bug'.
Message-ID: <295@aluxz.UUCP>
Date: Wed, 29-Jan-86 20:24:50 EST
Article-I.D.: aluxz.295
Posted: Wed Jan 29 20:24:50 1986
Date-Received: Fri, 31-Jan-86 23:47:10 EST
References: <11540@ucbvax.berkeley.edu.BERKELEY.EDU>
Organization: AT&T Bell Laboratories, Allentown, PA
Lines: 28

> 
> 	Recently, a friend of mine said that by firing up SuperCalc and then
> exiting his PCjr would perform nearly twice as fast as it did before using
> SuperCalc.  Thinking this behavior to be rather odd, I ran a bench mark
> program (the public domain dhrystone program distributed over net.sources)
> before and after the alleged speed increase.  Well, it was faster: 195
> dhrystones/sec before, and 396 dhrystones/sec after (the same as a PC).
> 
> 	Needless to say, I am curious about the cause of this serendipitous
> event, and if any of you happen to know the answer I would like to know why
> this happens.  Please post to the net (no e-mail), as I am sure others are
> interested as well.
> 
> Thanks,
> Tim Iverson.

On the PCjr with programs that run in the bottom 128K, the CPU and the
screen display must compete for memory cycle since there is no
separate screen memory.   Programs running above 128K run at same
speed as the PC (as long as they are not doing i/o like writing to
disk or screen).  The program he's running may reallocate the memory
and leave the new allocation when it exits.  Most memory expansion
units provide drivers to allocate the memory in various ways.


Robert Evatt                
AT&T Bell Labs, Allentown, PA
{ihnp4!aluxz!revatt}