From: rseymour@reed.edu (Robert Seymour)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Ram Disk Drive (solid state)
Date: 11 Nov 92 06:35:58 GMT
Article-I.D.: reed.1992Nov11.063558.29519
Reply-To: rseymour@reed.edu
Organization: Reed College, Portland, OR

In article <1992Nov10.195126.8596@iscsvax.uni.edu> simmons5275@iscsvax.uni.edu  
writes:
> Hi, I was recently looking through some back issues of radio electronics and
> found an interesting piece about a dsolid state disk drive made from static
> ram. I would be very interested in thins product except that it has capacity  
to
> store only 512k of info. Today 512k is nothing. I was wondering whether  
anyone
> has heard of a larger version, perhaps up to 64 meg :) That would interest me
> very much. The solid state drive must have ability to hold info when the  
system
> is turned off though or it wouldnt be of much interest to me. Imagine the
> access time on solid state static ram drive =). If anyone has info on either
> the existence or lack there of, id appreciate if they would send me the info
> withthe manufacturers name .. etc thanks.
> 
> 
> Robert
> 
> ======================================================================
> | Snail Mail Address :           | I just follow instructions.       |
> |   Robert E. Simmons Jr.        | After all my inteligence is only  |
> |   347 Shull Hall               | artificial. :)                    |
> |   University of Northern Iowa  |                                   |
> |   Cedar Falls, IA 50614        | -> "Dare to know." from 'What is  |
> | Email Address:                 | ->    Enlightenment' by Imannuel  |
> |   Look at the mail header!     | ->    Kant.  ca. 1850             |
> ======================================================================

	Solid state RAM drives are usually made of banks of DRAM (dynamic  
random access memory) and placed on a single card which is put into the local  
bus. Most often the card itself is just a bunch of SIMM slots and a few pieces  
of additional curcuitry. An SRAM card would have to be on the system bus to be  
useful (i.e. to make use of the additional speed of SRAM [SRAM c. 10-30ns, DRAM  
c.70-120ns].
	Most RAM drives are used for graphics manipulation where reading from  
disk at high speed is critical. They are very expensive (per megabyte compared  
to disk drives), and the new DRAM tariff won't help. I wouldn't suggest a drive  
unless you use high speed graphics programs and have an EISA bus. A better  
solution is a SCSI-2 fast and wide card with a RAID level 0 disk array (i.e.  
data-stripping, although level 3 or 5 may be fast enough with the new 3.5"  
large capacity drives).
	Another type of RAM drives are virtual RAM drives. These are crated by  
a partition in the main system memory. They have the advantage of being  
transferrable to main memory, and the software is cheap. Both of these types of  
RAM drives do not have backup power, so any information is lost on power-down.  
There are also some solid state external RAM drives which have an internal UPS,  
but they are extremely expensive and I couldn't imagine an application where  
they would be useful to a PC (the're mostly for supercomputers or very fast  
servers and workstations).
	Another example of RAM drives are the memory cards used in some  
handhelds or pen computers (also in calculators). They use a bank of SRAM with  
a battery (lithium) backup. However, they aren't feasable in high capacity at  
the moment. I gather that a RAM drive is not really what you need, a fast disk  
could do everything you need and be as fast as the PC can handle.

--
Robert Seymour				rseymour@reed.edu
Departments of Physics and Philosophy
Artificial Life Project			Reed College
Reed Solar Energy Project (SolTrain)	Portland, OR
Newsgroups: comp.sys.ibm.pc.hardware