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From: planting@cs.pitt.edu (Professor Harry Plantinga)
Newsgroups: comp.sys.mac.hardware
Subject: Re: LC Prediction (Was: New Macintosh Strategy)
Message-ID: <9087@pitt.UUCP>
Date: 6 Nov 90 22:51:25 GMT
References: <9037@ncar.ucar.edu>
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>Although the LC has a 68020 running at 16MHz (as does the Mac II), it is 
>configured with a 16-bit data path to memory instead of the 32-bit data 
>path of the Mac II. Since two bus cycles are required to read 32-bits  
>from memory on the LC (where only one bus cycle is required on the Mac II),  
>the LC is only half as fast as the Mac II, all other things being equal.

16-bit data path, yes; half the speed, not necessarily.

If I remember correctly, a data access on a Mac II has two wait states.  
That means that a memory access takes 3 cycles.  If memory access on a Mac 
LC has 2 wait states, it could be that the two transfers occur within 4 
cycles.  That would make the LC 75% the speed of the II.

Notice that I am not saying that this is the case.  I don't know anything 
about the Mac LC.  I'm just pointing out that the "half as fast" comment 
need not be true.  In fact, MacUser benchmarks make it much more than half 
as fast.




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Harry Plantinga
planting@cs.pitt.edu