Int 21H, AH=33H, AL=06H

5.0 and higher

GET TRUE VERSION NUMBER

      AX = 3306h

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

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 version 7.10

Heiko Goeman's Advanced WinDOS 2.10/2.11/2.21 returns DOS 5.00, revision 0.

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 SETVERed versions: 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

AH=30h,INT 2F/AX=122Fh,INT 2F/AX=E000h“SETDRVER”

Text based on Ralf Brown Interrupt List Release 61