Category: DOS kernel
INT 21 - DOS 5+ - GET TRUE VERSION NUMBER
AX = 3306h
Return: BL = major version
BH = minor version
DL = revision (bits 2-0, all others 0)
DH = version flags
bit 3: DOS is in ROM
bit 4: DOS is in HMA
AL = FFh if true DOS version < 5.0
Notes: this function always returns the true version number, unlike AH=30h,
whose return value may be changed with SETVER
because of the conflict from the CBIS redirector (see next
entry), programs should check whether BH is less than 100 (64h)
and BL is at least 5 before accepting the returned BX as the true
version number; however, even this is not entirely reliable when
that redirector is loaded
Under MS-DOS/PC DOS, DR DOS, PTS-DOS, S/DOS this function does not
use any of the DOS internal stacks and thus is fully reentrant
OS/2 v2.1 will return BX=0A14h (version 20.10)
Windows 95 and Windows 95 SP1 return version 7.00; Windows 95 OSR2
and OPK3 (OSR2.5) return version MS 7.10.
the Windows NT DOS box returns BX=3205h (version 5.50)
Novell DOS 7 returns IBM v6.00, which some software displays as
IBM DOS v6.10 (because of the version mismatch in true IBM DOS
mentioned for INT 21/AH=30h); versions through Update 15 all
return revision code 00h
Windows95 and Windows95 SP1 return version 7.00; Windows95 OSR2 returns
Heiko Goeman's Advanced WinDOS 2.10/2.11/2.21 returns DOS 5.00,
Novell DOS 7, OpenDOS 7.01, DR-OpenDOS 7.02, DR-DOS 7.02, DR-DOS 7.03
all return IBM 6.00, which some software displays as IBM DOS 6.10
(because of the version mismatch in true IBM DOS mentioned for
INT 21/AH=30h); versions through Novell DOS 7 Update 15.2 (01/1996)
all return revision code 00h. The DOS revision is stored in bits 7-0
of the "patch_version" field in the PCM_HEADER structure in the
IBMDOS.COM file (see also INT 21/AX=4452h !!!). The version
flags (DH) are stored in bits 15-8 of "patch_version", but is updated
at runtime to reflect the actual status. "patch_version" is also
reported as DX in INT 21/AX=4452h.
Unlike MS-DOS, under Novell DOS 7+ IBMDOS.COM will also allow to
SETVER the returned "true" DOS version same as with INT 21/AX=3000h
and INT 21/AX=3001h.
DR-DOS 7.02+ IBMDOS.COM (since 1998-01-10) now recognizes optional
paths to filenames stored in the SETVER list. Previously such
entries were never found. This enables a three staged model of
highest priority = entry with path is matching.
middle priority = entry without path is matching.
lowest priority = use global version (SETVER /G).
The DR-DOS 7.02+ SETVER 1.01+ (1998-01-12) has also been enhanced to
allow BDOS and DOS version faking (see INT 21/AX=4452h). In /X mode,
a set sub-version of y = 128..255 will be reported as 0..127 DOS
sub-version, sub-versions of y = 100..127 will be used to report this
value as BDOS version (64h..7Fh) with INT 21/AX=4452h instead while
bits 6-0 of the DOS revision stored in PCM_HEADER in the IBMDOS.COM
file will be used to report the BH DOS sub-version 0..127 (usually
this holds 0, but it can be patched to other values).
DR-DOS SHARE 2.05 (1998-01-05) has relaxed version checking now, and
will install on any DOS revision 0..127 (formerly it was bound to
DOS revision 0 only), as long as run on a DR-DOS 72h or 73h BDOS
kernel. Hence, if there will be changes in the SHARE implementation
without changing the BDOS version, DR-DOS SHARE 2.05 can still be
stopped from installing by changing the DOS revision in PCM_HEADER
to something in the range 128..255.
Under Novell DOS 7+, the version SETVERing also affects the version
number WORD stored at offset +40h in each program's PSP (see
Table xxxx at INT 21/AH=26h). This holds true even for special
sub-versions of 100..255 (see INT 21/AX=4452h).
S/DOS 1.0 (1995) returns a DOS revision of 9, while its own PTS OEM
revision still defaults to 0 (see also INT 21/AH=20h"S/DOS").
BUG: DR DOS 5.0 and 6.0 return CF set/AX=0001h for INT 21/AH=33h
subfunctions other than 00h-02h and 05h, while MS-DOS returns AL=FFh
for invalid subfunctions
SeeAlso: AH=30h,INT 2F/AX=122Fh,INT 2F/AX=E000h"SETDRVER"