Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 beta 3/9/83; site microsoft.UUCP
Path: utzoo!linus!decvax!microsoft!markz
From: markz@microsoft.UUCP (Mark Zbiokowski)
Newsgroups: net.micro.pc
Subject: RE: 99 files and 20 open files
Message-ID: <8656@microsoft.UUCP>
Date: Tue, 27-Sep-83 19:13:09 EDT
Article-I.D.: microsof.8656
Posted: Tue Sep 27 19:13:09 1983
Date-Received: Thu, 29-Sep-83 00:28:36 EDT
Organization: Microsoft Corporation
Lines: 22

MSDOS 2.0 maintains a set of FCBs for the system that are in the system-space
rather than in the user space.  The number of such FCBs is governed by the
FILES= statement in CONFIG.SYS.  The main advantage to having such FCBs and
other such structures in system space (and undocumented) is that system space
is controlled by the DOS; these structures may change for the benefit of the
DOS/applications without impacting those applications.

Now, as to why FILES=99 does not allow a process to open > 20 files is simple.
This is a fixed limit imposed on each process (created by EXEC system call).
The total number of files open may not exceed the FILES= number. Consider:

    process A opens 20 files
    process A EXECs process B
    process B closes all 20 files
    process B opens another 20 files

at this point, there are 40 files open although each process does not have
more than 20 files open at the same time.  The 20 number is fairly
reasonable: it comes from the default number of handles available under XENIX.

I wonder about applications the 'require' > 20 files open at a particular
time.