Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!hao!ames!amdahl!chuck
From: chuck@amdahl.amdahl.com (Charles Simmons)
Newsgroups: comp.arch
Subject: Re: Disk Striping (Really RAMs vs disks)
Message-ID: <12957@amdahl.amdahl.com>
Date: Wed, 26-Aug-87 14:35:56 EDT
Article-I.D.: amdahl.12957
Posted: Wed Aug 26 14:35:56 1987
Date-Received: Fri, 28-Aug-87 06:19:55 EDT
References: <cV=3A8y00UoB0qA0AT@andrew.cmu.edu> <414@astroatc.UUCP> <12718@amdahl.amdahl.com> <420@astroatc.UUCP>
Reply-To: chuck@amdahl.amdahl.com (Charles Simmons)
Organization: Amdahl Corp, Sunnyvale CA
Lines: 40

In article <420@astroatc.UUCP> johnw@astroatc.UUCP (John F. Wardale) writes:
>In article <12718@amdahl.amdahl.com> chuck@amdahl.amdahl.com (Charles Simmons) writes:
>>I was under the impression that not only did silicon memory double
>>in capacity every two years, but magnetic memory also doubled in
>>capacity every two years as well.
>
>My comments were in regard to disk *SPEED*  (Stripping, parrallel
>head disks....)

Doesn't increased capacity tend to imply faster disk speeds?  Faster
seek times in relation to the amount of data?  Faster bit transfer
times since the speed of the disk stays the same, but the number of
bits encountered by the head during a rotation increases?

>As RAMS get larger, it gets more practical to build reasonable
>sized RAM-disks (they may require more volume, and have higher $$/Mbyte 
>(if your claim is true), but could be a great deal if you need XX
>Mbytes at a certain (high) speed!!  

Yep...  I can't argue with this seeing as how the company I work for
sells a 1Gbyte ram disk.

>As I look into my crystal ball, I see RAM and optical (WO) disks
>replacing magnetic memory within 5 years...(say, ~~~  30% of total, 
>and 90% of new systems/designs)
>
>					John Wardale
>... {seismo | harvard | ihnp4} ! {uwvax | cs.wisc.edu} ! astroatc!johnw

Now I could see optical (read/write) disks taking over a substantial
portion of the market.  They don't seem to be intrinsically much more
expensive than magnetic disks.  However, its not clear that ram will
become as inexpensive as magnetic disks.  If ram is two orders of
magnitude faster and more expensive than magnetic (or optical) disks,
from a price/performance point of view, there is an optimal amount of
ram to buy to cache accesses to disk.  A ram cache nearly a thousand
times smaller than the disk farm can provide performance close to 90%
of having a ram disk farm, but the cost would be far less.

-- Chuck