Re: Zip GS questions

[spec@vax2.concordia.ca (Mitchell Spector)]

In article Mark Wade <mwade@suffolk.lib.ny.us> writes...

>On 11 Dec 1996 pubpc1@library.ucla.edu wrote:
>> That is very true.  I have a Zip running at 13.75MHz.  The actual chips
>> in the cache make up 64K (it used to be set at 64K).  The problem was,
>> it would not run stable.  When I reset the DIP switch configuration to
>> 16K of cache (even though the chips were still 64K w/all 4 sockets filled),
>> the board became very stable.
>>
>> I have not noticed much of a performance hit compared to 13.75/64 and the
>> extra megahertz definitely make it faster than when it was a 9/64.
> 
>If you set the DIP switches to 16k then that is all the cache that
>was being used despite what was installed on the board.  Even though
>you had 64k installed you were running as a 13.75/16 when you
>changed the DIP switch.  For that speed you want 30-45 ns chips
>in the DATA sockets and 15 ns chips in the TAG sockets.  With that
>configuration there is a good chance you could bump the switch up
>to 64k again.

    If your board is filled with 32K x 8 SRAMs (64K of cache) then
how is it possible to configure it to recognize only 8K or 16K of
cache memory? From my own experience, by flipping the DIP switches,
I can tell my card to "see" both 32K banks (64K) or only one of them
(32K). If I set the DIP switches for 8K or 16K, the ZipGS _instantly_
starts crashing and will be totally unusable. That is, it can't even
get as far as launching the Finder desktop because it then thinks 
there are lower-density chips installed.

    I would think if you want to toggle between 8K and 16K, you would
need 8K SRAMs in all four sockets. 

    In otherwords, if you have 8K or 32K of cache on your board (only
two sockets filled) there is no way to toggle the size. If you have a
board with 16K or 64K (four sockets filled) you _can_ toggle your cache
size, but only cut it by half by telling the board to ignore the second
set of chips. In my case I can toggle between 15/64 and 15/32, and on
my previous board I could toggle between 8/16 and 8/8. This is correct,
isn't it? (If not, someone please correct my assumption :)

Mitchell Spector
spec@vax2.concordia.ca