Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!ncar!ncar.ucar.edu!hpoppe
From: hpoppe@ncar.ucar.edu (Herb Poppe)
Newsgroups: comp.sys.mac.hardware
Subject: LC Prediction (Was: New Macintosh Strategy)
Message-ID: <9037@ncar.ucar.edu>
Date: 1 Nov 90 21:40:25 GMT
Sender: news@ncar.ucar.edu
Distribution: na
Organization: National Center for Atmospheric Research
Lines: 41
References:<306@cti1.UUCP> <272CAF47.16091@orion.oac.uci.edu> <2eBi026n031i01@JUTS.ccc.amdahl.com> <2730569E.19505@orion.oac.uci.edu>

In article <2730569E.19505@orion.oac.uci.edu> ajauch@orion.oac.uci.edu 
(Alex Jauch) writes:
> I have a Mac II (about the speed of a LC I presume) ...

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.

When pre-announcement rumors about the LC intimated it would have a 68020, 
I was disappointed. Since this was to be a low cost machine, it would be 
unlikely that they would offer the machine with a PMMU. That has turned 
out to be the case. So, no virtual memory in System 7.0 for the LC. 
However, when the machine was announced with a 16-bit data path instead of 
a 32-bit data path, my disappointment evaporated.

Why is that, you say?

Prediction:

The reason that the LC is not going into full scale production until 
January '91 is because the LC will not be built with a 68020! Instead, it 
will sport a Motorola 68025. As I recall from Motorola's announcement 
early last year, the 68025 is basically a 68030 with a 16-bit data bus. 
That is, it has on-chip PMMU. At the announcement, Motorola said that they 
and "a major computer manufacturer" would make a significant announcement 
in the summer ('90). To my knowledge, no such announcement was made. My 
guess is that the "major manufacturer" was to have been Apple with news of 
a 68025 LC, but the chip wasn't far enough along for the announcement to 
take place. Hence the delay in availability of the LC until January.

Of course, its possible that the 68025 will never see the light of day, or 
that it will be an LCx that has this chip. This chip is the equivalent of 
the 80386SX, and like that chip, could play an important role in low-cost 
desktop and portable Macs.

Herb Poppe             hpoppe@ncar.ucar.edu
NCAR                      (303) 497-1296
1850 Table Mesa Dr.
Boulder, CO  80307-3000