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From: amanda@visix.com (Amanda Walker)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Comparing the Mac+ and SE
Message-ID: <1991Apr26.191830.18589@visix.com>
Date: 26 Apr 91 19:18:30 GMT
References: <764@newave.UUCP> <1068@eplunix.UUCP>
	<1991Apr26.153645.5151@rodan.acs.syr.edu>
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Organization: Visix Software Inc., Reston, VA
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In article <1991Apr26.153645.5151@rodan.acs.syr.edu>
amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes:

   Wrong.  Code in ROM executes SLOWER because of the slow access
   times of the roms themselves.  If this weren't the case, you
   wouldn't see a drastic system improvement when you copy rom to ram
   (and you do, period).

Bzzzzzt.  Thank you for playing.

On the Macintosh Plus and SE (which the original poster was discussing),
ROM accesses are indeed faster than RAM accesses.  RAM is time-division
multiplexed between the CPU and the video circuitry, while the ROM is
not.  Since accessing RAM incurs up to four additional wait states, aggregate
ROM execution speed is (on average) from one one and a half to two
times faster than RAM, depending on stack and other RAM usage.

Check out the timing diagrams if you don't believe me.
--
Amanda Walker						      amanda@visix.com
Visix Software Inc.					...!uunet!visix!amanda
-- 
"An architecture in hand is worth 4 or 5 in vapor."	--Eugene Miya