Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!pasteur!ucbvax!hplabs!pyramid!prls!gert
From: gert@prls.UUCP (Gert Slavenburg)
Newsgroups: comp.sys.atari.st
Subject: Re: 16MHz board -- fast CPU, slow memory?
Summary: approximately 33 % gain
Message-ID: <11652@prls.UUCP>
Date: 19 May 88 00:34:54 GMT
References: <725@cacilj.UUCP> <5607@chinet.UUCP>
Reply-To: gert@prls.UUCP (Gert Slavenburg)
Organization: Philips Research Labs, Sunnyvale, California
Lines: 15

According to some local statistics of 68000's in operation, a crude
approximation is that a 68000 spends approximately half of its cycles 
internal and half externally (due to memory reference statistics). The 
external cycles still take the same amount of time, the internal cycles
go twice as fast. Hence, what used to take 'n' seconds, now takes
'0.75*n' seconds. Or at most a performance of 1.33 * that of an ST with
a 8 MHz processor.

Add to this the fact that there is an increased number of memory
requests per time unit, and hence more collisions with the video
accesses (if this applies on the ST, I'm not sure). This would
lower the performance a little more.

So you get somehwere between a 1.2 to 1.33 * speedup, roughly.
I wouldn't consider that enough of a speedup in relation to the
expected cost.