Path: utzoo!attcan!uunet!lll-winken!ames!mailrus!ncar!ico!rcd
From: rcd@ico.ISC.COM (Dick Dunn)
Newsgroups: comp.arch
Subject: Re: Solid State Secondary Storage
Summary: make a "solid state disk" - relatively old idea
Message-ID: <13487@ico.ISC.COM>
Date: 10 Jan 89 17:56:33 GMT
References: <248@vlsi.ll.mit.edu>
Distribution: comp
Organization: Interactive Systems Corp, Boulder, CO
Lines: 42

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.
...
> ...So we are left with a box that is:
> 	capacity of a few hundred megabytes,
> 	word addressable,
> 	much faster access than disk,
> 	much slower than ram,
> 	and around the same price as disk.

One characteristic you didn't mention is whether it's a volatile memory.
I assume you're not planning a battery backup, so it must be volatile. 
That makes a major difference in what it can be used for.

>...The Question Is:  What's it good for?...

Some time ago (late '70's), Storage Technology (then sTc, now StorageTek)
made an animal called a Solid State Disk.  The SSD was built in an era when
good fast RAM was a lot more expensive, but they were able to use
relatively less expensive RAM - a lot of it - and build something suitable
for paging space on IBM mainframes.  It was built to mimic the interface of
some particular small/fast disk (or drum? I forget).  One key point is that
if you use it for paging space it doesn't matter that it's a volatile
memory system.

Another old old idea to look at is the Extended Core Storage on the CDC
6x00s.  ECS was slow core memory (cycle time more than 3x main memory) but
it made up for this by a very wide data path (480 bits) to get an effective
transfer rate of 600 Mbit/sec.

If you can pull tricks to get the data paths wide enough that you get a
very high transfer rate, it could be an interesting product.  However, disk
arrays may offer you some competition in the higher range of storage
capacity, and memory sizes are creeping up from below...I wonder just how
the disk<->memory gap you're aiming at will look a year or two from now.
(That's not necessarily to say that it's closing, but it is certainly
moving.)
-- 
Dick Dunn      UUCP: {ncar,nbires}!ico!rcd           (303)449-2870
   ...Worst-case analysis must never begin with "No one would ever want..."