Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!cbmvax!jesup
From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.arch
Subject: Re: Extremely Fast Filesystems
Message-ID: <13667@cbmvax.commodore.com>
Date: 6 Aug 90 23:10:17 GMT
References: <5539@darkstar.ucsc.edu> <13285@yunexus.YorkU.CA> <30728@super.ORG>
Reply-To: jesup@cbmvax (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 38

In article <30728@super.ORG> rminnich@super.UUCP (Ronald G Minnich) writes:
>>puder@zeno.informatik.uni-kl.de (Arno Puder) writes:
>>| Tanenbaum's philosophy is that memory is getting cheaper and cheaper,
>>| so why not load the complete file into memory? This makes the server
>>| extremely efficient. Operations like OPEN or CLOSE on files are no
>>| longer needed (i.e. the complete file is loaded for each update).
...
>This is very elegant, but there is 
>a problem. We're running out of address bits again. 
...
>and stopped bothering with memory files. Obviously this applies
>to architectures we have now: lots of files are bigger than the 4 Gb address
>space of my Sun, and things are not getting any better. And of course on 
>Crays you don't get memory-mapped files at all. So the programs I now write
>that use memory-mapped files on SunOS always have an out in the event that the 
>mmmap fails or the system I am on does not support it. Conclusion: Bullet is 
>really cool, as are memory-mapped files, but their eventual utility is 
>limited by computer architecture questions. Since read-write is more general,
>maybe it is the wave of the future. Gee, i don't like that!

	I submit that your situation is something of an unusual case, and is
likely to remain unusual for at least a decade, perhaps 2.  Few machines
(percentage-wise) even have 4 GB of storage, let alone files larger that 4GB
(I've never even seen a file larger than 100MB, even on mainframes).

	Eventually, perhaps, but not in the near future.  There are people
who have greater needs, that's the whole justification for the selling of
supercomputers, and the vastly expensive (read fast & large) IO systems that
support them.  But they're a tiny minority, numbers-wise.  Until the
number of people that require such things increases sufficiently, the only
architectures to support the extra address bits will be the super-(and maybe
mini-super-)computers.  Those extra address bits are _not_ free, in silicon,
memory, etc.  (I hope we haven't started the 32+ addr bit rwars again...)

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.cbm.commodore.com  BIX: rjesup  
Common phrase heard at Amiga Devcon '89: "It's in there!"