From rei2!tsprad@uunet.UU.NET  Ukn Jul  9 17:38:46 1993
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From: rei2!tsprad@uunet.UU.NET (6692)
Message-Id: <9307092110.AA26534@rei.com>
Subject: Re: SIMMS
To: riscy@pyramid.com
Date: Fri, 9 Jul 1993 16:10:46 -0500 (CDT)
In-Reply-To: <9307091731.AA25233@rei.com> from "UUCP Login" at Jul 9, 93 12:31:52 pm
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> I've been thinking about memory.  I'm a software weenie, so if I've
> seriously mis-understood, please *gently* correct me.
> 
Same goes for me, too.

[Mucho memory in SIMMS]
> requires all that expensive 4-, 6-, or 8- layer M/B real estate.
> Plus drill holes through all those layers is not a pleasant thought (routing
> headaches, reliability, cost).  And 16 SIMM sockets ($).
> 
> Since Waldorf has (seems to have) agreed to produce boards that have surface
> mount components, would it be reasonable to mount discrete memory chips
> on the M/B?  Here was what I was considering:
> 
>   18 1Mbx4 70ns (is 70ns fast enough?) surface mount DRAMs on the M/B.
>       (18 because I assume the 3730 part wants parity bits)
>    8 standard SIMMs on M/B
> 
> Russell Kent
> 
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 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.

-- 
Ted Spradley   Recognition International, Inc.  Opinions are mine, not theirs.
2701 E Grauwyler Rd. |Your productivity is not enhanced when you're staring
Irving TX 75061      |at that thing.  Your productivity is enhanced when
214-579-6692         |the computer is working and you're doing something else.

 
From caret@pyramid.com  Ukn Jul  9 18:58:36 1993
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From: caret@pyramid.com (Neil Russell)
Message-Id: <9307092255.AA04310@sword.eng.pyramid.com>
Subject: Re: SIMMS
To: riscy@pyramid.com
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
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> 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

 
