Xref: utzoo comp.unix.microport:438 comp.unix.xenix:1891
Path: utzoo!mnetor!uunet!ncc!alberta!ubc-cs!grads.cs.ubc.ca!pajari
From: pajari@grads.cs.ubc.ca (George Pajari)
Newsgroups: comp.unix.microport,comp.unix.xenix
Subject: Re: RAM disk (WARNING: commercial content!)
Message-ID: <1962@ubc-cs.UUCP>
Date: 8 Apr 88 20:35:17 GMT
References: <1010@daisy.UUCP> <802@spdcc.COM>
Sender: nobody@ubc-cs.UUCP
Reply-To: pajari@grads.cs.ubc.ca (George Pajari)
Organization: UBC Department of Computer Science, Vancouver, B.C., Canada
Lines: 42

In article <1010@daisy.UUCP>, david@daisy.UUCP (David Schachter) writes:
>> With the recent discussion of problems running 9600 bps without losing char-
>> ... someone bemoaned the inability to define in-memory filesystems.  Is
>> there really no Unix driver to define in-memory simulated disk?

Driver Design Labs sells RAM-DISK drivers for SCO XENIX, IBM XENIX, (soon
Microport) and will port the driver to almost any machine given a good 
excuse (i.e. an order).

In <802@spdcc.COM> from: dyer@spdcc.COM (Steve Dyer)...
> XENIX 2.2 and above has a RAM disk driver, although I have never bothered
> to use it...

The 2.2 RAM disk driver suffers from several limitation which have been
addressed by the Driver Design Labs product:

With 2.2 the RAM disk size must be one of 16K, 32K, 64K, 128K, 256K, 
512K, 1M, 2M, 4M, 8M...  With the Driver Design Labs driver the RAM disk 
can be any size (in increments of 1K).

With 2.2 permanent RAM disks can only be resized or removed by rebooting
the machine.  With the Driver Design Labs driver the RAM disk can be 
created or removed at any time

With 2.2 the RAM disk is allocated at the next available memory location
leading to memory fragmentation.  With the Driver Design Labs driver the 
memory is allocated adjacent to previous RAM disks or at the high end of 
memory (whichever minimizes fragmentation).

In addition the Driver Design Labs driver comes with menu based utilities
to create and remove ram disks (avoids the need for a manual, although a
40 pages manual is included) and a utility which displays memory
utilisation graphically so that intelligent decisions can be made
regarding the allocation of memory.

All that aside, Steve's comments are correct...memory is usually best used
for buffers or by processes...but sometimes RAM disks can help (but probably
not when the problem is dropping characters with uucp).

George Pajari
(when not at UBC trying to finish an M.Sc. degree, programmer for
Driver Design Labs, (604) 926-UNIX)