Category: other operating systems
INT 21 - DR DOS 3.41+ - DETERMINE DOS TYPE/GET DR DOS VERSION
AX = 4452h ("DR")
Return: CF set if not DR DOS
AX = error code (see #01680 at AH=59h/BX=0000h)
CF clear if DR DOS
AX = version code
AH = single-user/multiuser nature (see #01581)
AL = operating system version ID (see #01580)
AL = operating system version ID (see #01579)
DX modified (refer to note below)
Notes: the DR DOS version is stored in the environment variable VER
use this function if looking for single-user capabilities, AX=4451h
if looking for multiuser; this call should never return multiuser
in DR DOS 3.41-6.0, DX=AX on return; for Novell DOS 7, DH=AH but DL=00h
(reportedly, DH=00h when booting NWDOS7 from installation disks)
Novell DOS 7 returns error code 0001h if SETVER x.255 is in effect for
the calling program, or SETVER /G x.255 is in effect
although based on DR DOS, CCI Multiuser DOS 7.xx,
IMS Multiuser DOS 7.x, and IMS REAL/32 7.50+ do not support this call
With OpenDOS 7.02 BETA 2 and DR-OpenDOS 7.02+, the install check
in most tools has been changed to run with both, AH=10h and AH=14h
to support possible future "client side" multiuser releases of
DR-DOS which may return 14h instead of 10h. Tools should also strip
off the CP/Net bit before checking the kernel version.
Often used version checks like >= 1070h are invalid, therefore,
hence the AH and AL must be checked seperately.
In DR DOS 3.31-6.0, and DR PalmDOS, DX=AX on return.
For Novell DOS 7 - DR DOS 7.03 the DX value returned by this function
is the same as the DX value returned by INT 21/AX=3306h, and
represents the DOS revision (bits 7-0, currently always DL=00h) and
the version flags (bits 15-8, with bit 12 = DOS in HMA, bit 11 = DOS
in ROM) of the "patch_version" field in the PCM_HEADER structure in
the IBMDOS.COM file. The version flags, however, are updated at
runtime to reflect the actual system status, resulting, for example,
in DH=10h for DOS in HMA, and DH=0 when booting Novell DOS 7 from
The operating system version ID represents the BDOS (Basic Disk
Operating System) kernel version (of the DRBDOS.SYS aka IBMDOS.COM
file), and the two nibbles can actually be read as CP/M version
and sub-version, that is DR-DOS 7.03 (version code 1073h) is
actually CP/M-86 version 7.3.
Due to lost original patch sources from the backups, Caldera OpenDOS
7.01 merely represented Novell DOS 7 Update 10 with minor changes.
For Caldera DR-OpenDOS 7.02, all the Novell DOS 7 patches up to
including Update 15.2 have been re-incorporated into the system
from other sources, while the missing patches for IBMBIO.COM were
independently re-implemented by Matthias Paul in 07/1997-10/1997.
Novell DOS 7 (since 1993-11-08), OpenDOS 7.01 and OpenDOS 7.02 BETA
IBMDOS.COM return error code 0001h if SETVER x.255 is in effect
for the calling program, or SETVER /G x.255 is in effect.
Since Caldera DR-OpenDOS 7.02 the SHARE 2.05+ (1998-01-05) driver
uses INT 21/AX=65A2h as an *additional* BDOS version check: If the
"FUCASE char" function is functional on a DR-DOS BDOS kernel 72h+,
SHARE assumes it is running on an OpenDOS 7.02 BETA 1 (73h) kernel
(or later) even if the BDOS version returned by INT 21/AX=4452h would
indicate an earlier issue of the kernel. Some 3rd party drivers
(like HPFS_DOS.EXE) were hardwired to detect Novell DOS 7 only,
and so the kernel version had to be patched back on such systems
to allow such drivers to work properly. The BDOS version and DOS
revision are stored in PCM_HEADER of the IBMDOS.COM file, see
table XXXX below.
However, this is no longer necessary with the introduction of the
DR-DOS 7.02+ IBMDOS.COM (since 1998-01-10) and SETVER 1.01+
(since 1998-01-12) because they allow to fake BDOS versions as well
as faking DOS versions. In /X mode, a set sub-version of y = 100..127
will be used as BDOS version instead (64h..7Fh), while the DOS
revision will be used to report the DOS sub-version instead. For
example, given a DOS revision of 0, SETVER 6.114 would be the proper
value to fake Novell DOS 7 (114=72h) on a DR-DOS 7.02+ system,
reporting a DOS version of "IBM" 6.00. Sub-versions 128..255 will
completely disable this BDOS version check, and report a DOS sub-
version of 0..127. This is to work around problems with possibly
hostile programs, that try to detect DR-DOS to not run on this OS.
Additional version check for 1072h kernels: At API level, there
is no known way to distinguish Novell DOS 7 from OpenDOS 7.01,
however, an IBMBIO.COM/IBMDOS.COM file date since 1997 and the
existance of an environment variable %OS%=OPENDOS usually indicates
an OpenDOS system (but not the other way around; some OpenDOS
BETAs still used %OS%=NWDOS!).
Additional version checks for 1073h kernels: A functional test of
INT 21/AX=65A2h (see above for SHARE) can be used to distinguish
OpenDOS 7.02 BETA 1 from the later (OpenDOS 7.02 BETA 2+ and)
DR-OpenDOS 7.02 and DR-DOS 7.02 releases, which are both the
same, except for the name change and minor bug fixes. Testing
for the INT 21/AX=6601h/BX=0000h bug can be used to differentiate the
original release of DR-DOS 7.02 from later 7.02 updates and
The DR DOS version is stored in the environment variable VER.