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From: jfw%mit-ccc@BRL.ARPA
Newsgroups: net.unix-wizards
Subject: Re: Ram Disks
Message-ID: <3852@sri-arpa.UUCP>
Date: Thu, 4-Aug-83 20:55:41 EDT
Article-I.D.: sri-arpa.3852
Posted: Thu Aug  4 20:55:41 1983
Date-Received: Sun, 7-Aug-83 02:59:57 EDT
Lines: 16


About disk speeds:  your swapping disk wants to have a high transfer rate,
but can have slow access time:  you are going to tell it to find sector 3216
and transfer 50Kb.  Your filesystem disks want to have fast access time, but
can have slow transfer rates (relatively), because you are only going to do
512 byte (1K) transfers, in general.  I ran through this exercise when I found
an old RF-11 disk in our junk heap.  Though I thought it would be great for
swapping (relieve our tired CDC disk!), I discovered that it's fast access
time (it is a fixed-head head-per-track disk) and miserably slow transfer rate
would have made it adequate for filesystem use (expected throughput equal to our
CDC 9762), but would have been miserable for swapping -- the break-even point
was exactly 512 bytes...

At Lincoln Lab's now-defunct Applied Seismology Group, we had a "memory disk"
which consisted of the last .5M of our 11/44 address space.  It was used for
a couple of programs which were quite disk intensive of temporary files.