Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!uunet!mcsun!hp4nl!dutrun!duteca!knop
From: knop@duteca (P. Knoppers)
Newsgroups: comp.sys.atari.st
Subject: Re: Memory speeds of ST & STE
Summary: 150 ns is sufficiently fast for 8 MHz 68000
Message-ID: <729@duteca.UUCP>
Date: 27 Feb 90 12:52:03 GMT
References: <1990Feb24.222700.22004@newcastle.ac.uk>
Reply-To: knop@duteca.UUCP (Peter Knoppers)
Organization: Delft University of Technology, Dep. of Electrotechnical engineering.
Lines: 34

In article <1990Feb24.222700.22004@newcastle.ac.uk> D.C.Halliday@newcastle.ac.uk (D.C. Halliday) writes:
>Can someone out there tell me what memory speed is required for the
>STe or standard ST. (I suspect 100ns) Also if I use faster memory such
>as 70ns will asyncronous tasks such as burst filling a 16Mhz
>Hypercache or DMA access will these be faster?

I recently upgraded my 1040 STf to 2.5 MB. I have now 16 256kbit chips
that are rated 150 ns on my shelve doing nothing (any takers ?). So the
answer to your first question is: 150 ns is sufficiently fast for an
8 MHz MC 68000. (Does the STe run on 8 MHz ?)

As to the second question, no, I would not expect DMA to be able to 
exploit faster RAM chips. I don't know what Hupercache is, but unless 
it is hardware, it can not exploit faster RAM chips.
By the way, even if it could, the improvement in performance would be
negligible, because access times for a hard disk are in the order of
25 ms. Transfer rate to the computer must be extremely slow to make
any difference.

>With the new MMU in the STe and spare/reserved bit patterns in the
>memory configuration can the STE's memory be expanded beyond 4MB. (I
>guess adding a new bank size of 8MB would be possible thus allowing
>the full 16MB of address space.) any comments?

Well, I would expect the new MMU to be an improvement over the old one.
However, the full 16 MB address range can never be dedicated to RAM,
because then there would be no space left for ROM and I/O. I have no
documentation on the new MMU, so this is only educated guesswork.
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P. Knoppers, Delft Univ. of Technology, The Netherlands, knop@duteca.tudelft.nl