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From: akes@mcshh.hanse.de (Andreas Kessemeier)
Newsgroups: comp.os.msdos.misc
Subject: Re: Max files open
Message-ID: <8159@mcshh.hanse.de>
Date: 5 Oct 90 16:28:34 GMT
References: <6548@castle.ed.ac.uk>
Lines: 50

elev66@castle.ed.ac.uk (G Gaston) writes:
>[Question about more then 20 Files in one Process under MSDOS]

The Value of FILE= is not the only Value, which restricts the max. Number
of open Files. There is a 'per Prozess' Table of open Files in the
PSP (Programm Specifikation Block) of an executing Programm. This Table
is initialized to 20 Entrys on Startup. There is not Way to tell MSDOS,
to setup a larger Table, but you can do this on Startup in your Programm.

- At Offset 28 in the PSP there is a Table of 20 Bytes. Each Byte
  has the Value 255, if the File is not open.

- At Offset 56 in the PSP there is a Word containing the maximum
  Number of open Files. In the normal case the Value of this Word is
  20 (see above).

- At Offset 58 in the PSP there is a Doubleword - Pointer to the
  Table of open Files. This Pointer points initially to the above
  mentioned Table.


To expand the Table of open Files, do the following:

- Allocate a new Table, large enough to hold the Number of Entrys you
  want.

- Copy the old Table (all 20 Entrys) into the new Table and initialize
  the remaining Entrys to 255.

- Redirect the Pointer at Offset 58 to your new Table an update the
  Word at Offset 56 to the Size of yout new Table.


Please Note:
	I have never tested this extensively, but it's same Way
	some Network - Shells are setting Things up. I have never
	heard of Problems with that.


OOPS, before i forget: All Numbers are in Dezimal.


Greets,
	Andreas

-->
Andreas Kessemeier 
Smart  : akes@mcshh.hanse.de
Bang   : Need no steenking Bangs!
Spruch : Wenn alles laeuft, dann haben wir irgendwas vergessen (Murphy)