Path: utzoo!utgpu!attcan!uunet!tank!ncar!ames!think!dbs
From: dbs@think.COM (David B. Serafini)
Newsgroups: comp.arch
Subject: Re: Solid State Secondary Storage
Keywords: ram, wafer, disk, SSD
Message-ID: <35258@think.UUCP>
Date: 7 Jan 89 06:56:30 GMT
References: <248@vlsi.ll.mit.edu>
Sender: news@think.UUCP
Reply-To: dbs@fafnir.think.com.UUCP (David B. Serafini)
Distribution: comp
Organization: Thinking Machines Corporation, Cambridge MA, USA
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.
>
>The Question Is:  What's it good for?  How might it be integrated into 
>existing computer (or other) systems?  What new systems or applications
>would it make feasible?

Well, Cray has made a lot of money selling Solid State Disk (SSD)
which are nothing but huge ramdisks.  They're useful for solving
really large problems that have locality of reference or block
algorithms.  Using double-buffered asynch i/o you can make the
transfer time overlap useful computation.  It can also help the
operating system keep lots of processes alive by allowing for fast
swapping.  More generally, I think this could be used to support
virtual memory quite well.  I don't know if anyone has ever tried
this on a Cray.  A segmented OS like Multics might really benefit 
from this capability.

>What if we could put a little matching circuit on each wafer to support
>context addressable usage?  What other sort of additional (small) circuits
>would be useful in such a beast?

Virtual memory could be supported by hash tables or CAM's.  The
Multics dynamic linking used special hardware in the GE640 (?) to
make deref'ing the links fast. A table of these might help.

>What do people use the current (small & expensive) ram-disks for now?

Scientific problems of all kinds need lots of memory.  I know the
computational chemists at NASA/Ames can consume over a 100MW
(800MB) of core/SSD per job.  NEC and IBM also provide multi-GB
extended memory on their biggests machines.  Sorting very large
datasets would really win big.  Maybe putting comparison hardware
on chip would be useful.

>George Young,  Rm. B-141		young@ll-vlsi.arpa
>MIT Lincoln Laboratory			young@vlsi.ll.mit.edu
>244 Wood St.
>Lexington, Massachusetts 02173		(617) 981-2756

*************************************************************
-David B. Serafini				dbs@Think.Com
Thinking Machines Corp.
Mathematical and Computational Sciences
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