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To: riscy@pyramid.com
Subject: Re: SIMMS
From: caret@pyramid.com (Neil Russell)
Date: Fri, 9 Jul 93 15:55:53 PDT
In-reply-to: <9307092110.AA26534@rei.com>; from "6692" at Jul 9, 93 4:10 pm
Reply-to: riscy@pyramid.com
Sender: riscy-request@pyramid.com
> If the answers to Russell's questions (which I deleted) are positive
> I think this is a good idea.  It raises the base price of the board,
> but a board with _no_ memory is worthless anyway.  For me,
> personally, 32 MegaBytes in surface mount and no SIMMS would be OK,
> but I realize that the amount of memory people want, and want to pay
> for, varies wildly.  Russell's compromise addresses that.

I have no figures but I would guess that we could get SIMMs for
cheaper than the equivalent DRAM chips.  My guess is that they would
take about 3 times the board space as the equivalent SIMM.  Also,
the cost of doing SMD placement is proportional to the number of
components you want to mount, to keeping this number down would
be useful.  Finally, many of us already have SIMM memory modules
that we could put onto this board; I for one will be replacing a
386 MB with this thing.

As for interleaving, you need 64-bits of the same type of memory
to interleave two banks.  It should be possible to interleave the
first 8 MB, and not the next 4 MB, or have 4 MB SIMMS in the first
two banks, and 1 MB SIMMS in the next two banks.

> I guess the real key is whether Waldorf can put surface mount
> components on both sides of the board.  There is probably very
> little difference between SIMM sockets and surface mount if it's all
> on one side of the board.

SMD on the other side is a *real* pain to assemble, and thus costs $$$.
The method used for the top side is to put solder paste onto the SMD
pads, place the components, then heat the board up in an I/R oven,
which melts the paste and literally sucks the component into the
corrent position.  For SMD on the underside, its the same, unless
you also have through hole stuff (which we do), then you have to glue
the components onto the underside (after you have done the top side),
then place all the through hole stuff on the top, then run the board
through a wave solder machine.  You have to play a fair bit to get
the SMD parts to stay in place on the solder wave; you end up trashing
a few boards and components.

Lets stick to SIMM sockets...

Neil Russell            (The wizard from OZ)
Pyramid Technology                      Email:  caret@pyramid.com
3860 N. First Street                    Voice:  (408) 428-7302
San Jose, CA 95134-1702                   FAX:  (408) 428-8845


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