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From: gus@Shasta.ARPA
Newsgroups: net.micro.mac
Subject: Re: New Product Idea: external ram disk
Message-ID: <5044@Shasta.ARPA>
Date: Tue, 30-Apr-85 15:20:23 EDT
Article-I.D.: Shasta.5044
Posted: Tue Apr 30 15:20:23 1985
Date-Received: Fri, 3-May-85 07:59:42 EDT
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Organization: Stanford University
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> In a similar vein (novel sorts of RamDisks), how about a "smart"
> ramdisk that does data compression/decompression on the fly?  I'd
> take odds that the actual information content of an apparently full
> 400k floppy could be expressed in less memory at some cost in 
> coding/decoding.  Packbits might be the fastest and easiest way to
> go (although not necessarily the most space-efficient).  Now your
> puny 316k ramdisk can contend with your beefy 400k floppies! :-)

Data compression kills performance. Try out something like compace/
uncompact/ccat on UNIX and you will see what I mean. Packbits is nice
for repetative data such as MacPaint pictures, but not for less
regular data such as 68K code. (what you will normally put on your
RAMdisk.)

Face it, folks, RAM disks are supposed to be FAST. Any optimizations
would slow them down to floppy speeds making them useless for what they
were intended. I think you guys are all on the wrong track. Sure, you
could figure out some neat new external Ramdisk, internal kludge, etc.
but this will not give an order of magnitude better performance.
The next step is to shell out real $$$ for new hardware such as a hard drive.

There is one exception - a disk cache. This will cache blocks read into
memory from disk so that they don't have to be read-in again. For example
the first time you load the finder, it loads at floppy speeds. The second
time, it comes in at RAMdisk speeds. This has certain advantages and 
disadventages to a RAMdisk which is pre-loaded at boot time. It is safe
to say that a disk cache (such as the turbobuffer) is in the same
realm as a ramdisk as far as functionality is concerned.

						Gus Fernandez