🚀 go-pugleaf

In article <1992Aug10.172308.188696@zeus.calpoly.edu> rmathews@zeus.calpoly.edu (Bob Mathews) writes:
>kr@jet.uk (Kenneth Reed) writes:
>>I don't use Windows myself, but I was just musing about how it gets the
>>multiple DOS sessions to work in 386 enhanced mode.
>...
>>For example, take 2 processes writing to a file "simultaneously". They
>>both come along and find out what blocks are free and let's assume
>>that the information stays withing the DOS buffers so they don't need
>>to go back to disk again. What stops both processes trying to use the
>>same "free" blocks?
>>
>>Anyone got any ideas on how it works?
>
>The usual solution for parallel processing is to simply disallow anything
>that causes a problem.  I don't really know anything, but my guess is that
>they _don't_ run separate instances of dos.  Just separate instances of
>command.com.  Each one has its interrupts tweaked so that its dos requests
>get handled by whatever operating system is running things.  Now, if
>one of them is trying to do direct disk-level i/o on its own (like a
>hard disk defragmentation program) it'll kill everything.  Which is why
>they warn you not to run such programs.
>

I think that you are close to the answer.  All calls to the disk probably go 
thru 1 source under Windows, queueing 'em up to execute 1 at a time.  This is 
why such things as format in a dos window hoggs the machine.  OS's such as 
OS/2 and Windows NT go about it entirely differently (via locks and such) so 
that it is not as much a problem.

-- 
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