Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uflorida!novavax!hcx1!monty
From: monty@SSD.CSD.HARRIS.COM (Monty Norwood)
Newsgroups: comp.realtime
Subject: Re: real-time multicomputer systems
Message-ID: <4328@hcx1.UUCP>
Date: 30 May 90 14:29:15 GMT
References: <11986@shlump.nac.dec.com>
Sender: news@hcx1.UUCP
Organization: Harris Computer Systems, Fort Lauderdale, FL
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The benefit of contiguous files is indeed the elimination of seek times.
As noted by many posters to this group, the success of this is dependent
on many things, not just the contiguous nature of the file.

The primary benefit is in cases where a disk, in a real time application,
is dedicated as an archive. Essentially a large circular (possibly) buffer
saving the last x seconds, minutes, or hours of the raw data gathered.
Telemetry applications often need this. Missile range stuff where raw data
comes in fast and furious but only for a short duration of time can benefit
from this use.

On the Night Hawk system, contiguous disk files are typically used with the
direct disk I/O feature (bypassing the buffer cache) so that large chunks of
data can be written to the disk on a periodic basis as quickly as possible.
These features are intended to be used in stringent real time environments
where the environment is controlled. 

Clearly, if there is other activity to the same disk or the accesses to the
file are random (as opposed to sequential) then all the noted problems 
in other postings make this feature a moot point. Expanding the file is
indeed a problem.

It is not perfect, but very useful in some applications, particularly real
time.