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From: phil@amd70.UUCP (Phil Ngai)
Newsgroups: net.micro.68k,net.micro.16k
Subject: Re: 68020 vs 16k
Message-ID: <4313@amd70.UUCP>
Date: Thu, 9-Feb-84 15:23:50 EST
Article-I.D.: amd70.4313
Posted: Thu Feb  9 15:23:50 1984
Date-Received: Fri, 10-Feb-84 07:12:57 EST
References: <1646@rocksvax.UUCP>
Organization: AMD, Santa Clara, CA
Lines: 28

I can't let this one go by. Intel, feel free to respond also.

> Beware of the benchmarks that sound real impressive, but require you
> to use VERY fast memory to acheive as I have heard about some of the
> faster versions of the 286 (not a put down on Intel, but their sales
> lit which seems to always compare benchmarks is on CPU's often has
> looked real good on paper, but has not turned out the same in a system).
> 					Norm Zeck

The 286 does not require VERY fast memory, at least, for a given
memory bandwidth, the 286 will run with slower access memories than
the 68000 will. The 286 has a separate address and data bus, just
like the 68000. However, they do something useful with it. They overlap
the data operation of the current cycle with the address of the next
cycle. For example, with an 8 MHz 286, a word is required every 250 nS.
However, the required memory access time is a leisurely 242 nS.

To run a 68000 with an 8 megabyte per second memory bandwidth would
require a 16 MHz 68000. The required memory access time in that case
would be about 156 nS (address strobe in state 2, data required
end of state 6, 5 states * 31.25 nS per state = 156.25 nS).

Of course, if you have 156 nS, you probably need 100 nS DRAMs.
This is expensive.

Perhaps intelca!kds could comment on my analysis.
-- 
Phil Ngai (408) 988-7777 {ucbvax,decwrl,ihnp4,allegra,intelca}!amd70!phil