Path: utzoo!attcan!uunet!mcvax!ukc!warwick!inmos!mcwill
From: mcwill@inmos.co.uk (Iain McWilliams)
Newsgroups: comp.arch
Subject: Re: Solid State Secondary Storage
Keywords: ram, wafer, disk
Message-ID: <697@brwa.inmos.co.uk>
Date: 12 Jan 89 10:22:56 GMT
References: <248@vlsi.ll.mit.edu>
Reply-To: mcwill@inmos.co.uk (Iain McWilliams)
Distribution: comp
Organization: INMOS Limited, Bristol, UK.
Lines: 50

In article <248@vlsi.ll.mit.edu> young@vlsi.ll.mit.edu (George Young) writes:
>
>Our wafer scale integration group is considering developing a new kind
>of computer memory unit -- something we hope might fill in the present
>gap in memory speed and price between magnetic disk and ram.
>
>Suppose you had a unit composed of a stack of silicon wafers, maybe ten or
>twenty of them.

[Munch Munch Munch ... Brpppp !!!] 

>Comments, raves, dreams, musings welcome by e-mail. 
>Please, this is only a PROPOSED project, no real specs exist yet, so don't
>ask where you can buy one :-).
>
>George Young,  Rm. B-141		young@ll-vlsi.arpa
>MIT Lincoln Laboratory			young@vlsi.ll.mit.edu
>244 Wood St.				[10.1.0.10]
>Lexington, Massachusetts  02173		(617) 981-2756

I remember reading about wafer scale integration as much as four or five
years ago. Then, the main problems to be solved were coping with flaws
on the wafer. This is because four flaws on a wafer of 'normal' RAM
chips could decrease your yield from 100 to 96 chips. ( Not that much of
a problem )

However if you have flaws on a WSI there are two possible circuits that
could be effected.

i)	A RAM chip/module. 
	This wouldn't cause that much grief as your control circuitry
should be able to mark that module as bad and still function normally.
Something similar to a disk o/s marking blocks as bad in the FAT.

ii)	The control circuitry.
	This is the biggie, if the control/data paths are hit then
unless you have backup control circuits, you could loose a large
percentage of the storage capacity on the wafer. Again it can be
compared with a disk, getting a bad block within the FAT.

As I said I remember reading about these problems four or five years
ago. So I don't even know if these are still regarded as the main
difficulties in building WSI Memory Modules. However, if they are it
would be interesting to hear how you plan on overcoming them.

-- 
Iain McWilliams     Inmos Ltd, 1000 Aztec West, Almondsbury, Bristol, BS12 4SQ
------------------------------------------------------------------------------
The opinions above are my personal views and do  | 
         not refelect Inmos policy.              |    mcwill@inmos.co.uk