please dont rip this site


* Get/set option marking character (is usually "/"), and device type

entry AH 37h

AL 00h read switch character (returns current character in DL)

01h set character in DL as new switch character

(DOS 2.x) 02h read device availability (as set by function AL=3) into

DL. A 0 means devices that devices must be accessed in

file I/O calls by /dev/device. A non-zero value means

that devices are accessible at every level of the

directory tree (e.g., PRN is the printer and not a file


AL=2 to return flag in DL, AL=3 to set from DL (0 = set,

1 = not set).

(DOS 2.x) 03h get device availability, where:

DL 00h means /dev/ must precede device names

01h means /dev/ need not precede device names

return DL switch character (if AL=0 or 1)

device availability flag (if AL=2 or 3)

AL 0FFh the value in AL was not in the range 0-3.

note 1) Functions 2 & 3 appear not to be implemented for DOS 3.x.

2) It is documented on page 4.324 of the MS-DOS (version 2) Programmer's

Utility Pack (Microsoft - published by Zenith).

3) Works on all versions of IBM PC-DOS from 2.0 through 3.3.1.

4) The SWITCHAR is the character used for "switches" in DOS command

arguments (defaults to '/', as in "DIR/P"). '-' is popular to make a

system look more like UNIX; if the SWITCHAR is anything other than '/',

then '/' may be used instead of '\ or pathnames

5) Ignored by XCOPY, PKARC, LIST

6) SWITCHAR may not be set to any character used in a filename

7) In DOS 3.x you can still read the "AVAILDEV" byte with subfunction 02h

but it always returns 0FFh even if you try to change it to 0 with

subfunction 03h.

8) AVAILDEV=0 means that devices must be referenced in an imaginary

subdirectory "\\dev" (similar to UNIX's /dev/*); a filename "PRN.DAT"

can be created on disk and manipulated like any other. If AVAILDEV != 0

then device names are recognized anywhere (this is the default):

"PRN.DAT" is synonymous with "PRN:".

9) These functions reportedly are not supported in the same fashion in

various implementations of DOS.

10) used by DOS 3.3 CHKDSK, BASIC, DEBUG

file: /Techref/INT/21f/37.htm, 2KB, , updated: 1999/2/20 10:26, local time: 2024/2/22 15:26,

 ©2024 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?
Please DO link to this page! Digg it! / MAKE!

<A HREF=""> INT 21f 37</A>

After you find an appropriate page, you are invited to your to this massmind site! (posts will be visible only to you before review) Just type a nice message (short messages are blocked as spam) in the box and press the Post button. (HTML welcomed, but not the <A tag: Instead, use the link box to link to another page. A tutorial is available Members can login to post directly, become page editors, and be credited for their posts.

Link? Put it here: 
if you want a response, please enter your email address: 
Attn spammers: All posts are reviewed before being made visible to anyone other than the poster.
Did you find what you needed?


Welcome to!


Welcome to!