RAM disk vs paging + buffer cache

[Eriks Rugelis]

In article <2979 at brl-smoke.ARPA> gwyn at brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>) writes:
>In article <514 at opus.nbires.UUCP> rcd at nbires.UUCP (Dick Dunn) writes:
>>What generally-useful features does a RAM disk have that I didn't
>>consider?
>
>The way I look at it, a RAM disk is just one way to exploit cheap
>semiconductor technology within the existing model of computation.
>RAMs for such use will normally be slower than main memory RAM,
>therefore more affordable (min $/bit).  Multi-level storage is the
>rule with large systems; ideally it would be transparent (as in
>Multics), but in practice "permanent storage" (disk) is different
>from "temporary storage" (core).
>
>The RAM disk on my Apple //e is useful because the Apple main
>memory management is a botch..

i recently went to a conference/tradeshow with exactly this premise in mind
and came away with a different view of the world...  the key here is
'affordability'...  it is in some ways an unfortunate reality that there is
no market and no real supply of 'old technology' semi-conductor memory
parts...  just about as soon as they are able, semi-conductor manufacturers
ramp up production of the latest and greatest generation of memory devices...
hence they don't tend to produce lower density parts for very much longer

the bottom line is that semi-conductor disks tend to cost MORE per mega-byte
because they are made from the same parts as regular memory boards but must
also include a whole bunch of extra logic to support some sort of standard
disk interface personality

the comments that i heard mostly pointed in the direction of loading up one's
cpu with memory and working towards enhancing one's ability to cache data
in main storage and thus reduce the need to go to disk

you can afford to use a RAM disk on your apple because you don't really
need all that much of it... in my case, i don't think that anything less
than 70 to 100 mega-bytes would suit my ideal case solution (i run about
10 vms vaxen and some sun's) since vms pages from the file system i would
need to put a fair chunk it in my ideal semi-disk configuration

does anybody out there have some real experience to comment on?  i for
one would be glad to hear about it

-- 
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