Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!samsung!munnari.oz.au!csc!ccadfa!cancol!ross
From: ross@cancol.oz (Ross Johnson)
Newsgroups: comp.sys.ibm.pc
Subject: Re: More than 15 files open
Message-ID: <274@cancol.oz>
Date: 10 Jan 90 00:43:54 GMT
References: <1989Dec17.150044.18175@axion.bt.co.uk> <5831@eos.UUCP> <1989Dec19.161509.10803@mks.com>
Organization: Info. Sci. and Eng., University of Canberra
Lines: 35

In article <1989Dec19.161509.10803@mks.com>, andy@mks.com (Andy Toy) writes:
> Here's some more information that may be helpful that someone else
> here pointed out to me.
> --
> 2) The 20 file limit of the file descriptor table per process may be increased
>    by putting a different pointer into the PSP (currently there is a
>    seg:offset address inside the PSP to a 20 byte area in the PSP for
>    the file descriptor codes).  This can be pointed to any other location
>    and a new size given (e.g. 200 open files).  The limit is probably
>    255 because FF is reserved to mean that that entry is closed)

For my own interest, I looked up the PSP description in Thom Hogan's "The
Programmer's PC Sourcebook" and can add the following details:

(As of DOS3.3):
	PSP Offset 18H: Handle Table (20 bytes). Usual contents are FFH =
	slot available. One byte per handle, bit 7 = not inherited (I presume
	this means you can have 128 files inherited by child processes and
	127 files which aren't).

	PSP Offset 32H: Handle Table size (2 bytes). Usual contents are
	14H,00H.

	PSP Offset 34H: Handle Table address (if not at 12H - 4 bytes).
	Usual contents are 12H,00H,00H,00H (0000:0012H).

(Hope I have the byte orders correct.)
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