Path: utzoo!attcan!uunet!samsung!dali.cs.montana.edu!rpi!crdgw1!sagittarius!dixon
From: dixon@sagittarius.crd.ge.com (walt dixon)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Retrieving the value of FILES=???
Keywords: Global File Handle Table
Message-ID: <8550@crdgw1.crd.ge.com>
Date: 14 Jun 90 14:31:44 GMT
References: <605@digigw.digital.co.jp>
Sender: news@crdgw1.crd.ge.com
Reply-To: dixon@sagittarius.crd.ge.com (walt dixon)
Organization: General Electric Corp. R&D, Schenectady, NY
Lines: 47

In <605@digigw.digital.co.jp> Gordon Day writes:

>I am confronted with the problem of finding out length of the global file
>handle table in DOS (>=3.3).  I am aware of the following issues:

[text deleted]

The MS-DOS Technical Reference Encylopedia (at least the first edition)
referred to this structure as the System File Table or SFT for short.
DOS maintains the base address of the SFT in a list returned in es:bx
by int 21h ah=52h.  Specifically es:[bx+4] is a dword ptr to the system
file table.  The system file table is organized as a linked list with
the following format:

  +------------------+
  | link to next     |
  | block of entries |
  | (DWORD)          |
  +------------------+
  | entries in this  |
  | block            |
  | (WORD)           |
  +------------------+
  |  1st SFT entry   |
  |  in block        |


  |  last SFT entry  |
  |  in block        |
  +------------------+

You can determine the SFT size by walking the list and adding up the entries
per block.  You can also determine available/used space by looking at the
reference count in the individual SFT entries within each block.  There's
a more complete explaination of the SFT as well as other interesting DOS
data structures in Chapter 10 of "The MS-DOS Papers" (Howard Sams, 1988).
BTW I am the author of this chapter and the following one on device
drivers.  I derrive no revenue from book sales;  I'm just citing a good
reference.

Walt Dixon	{internet:	dixon@crd.ge.com	}
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Walt Dixon dixon@crd.ge.com