INT 21 - Concurrent DOS v3.2+ - INSTALLATION CHECK AX = 4451h Return: CF set if not Concurrent DOS AX = error code (see #01680 at AH=59h/BX=0000h) CF clear if successful AH = single-user/multiuser nature (see #01581) 10h single-user AL = operating system version ID (see #01580) 14h multiuser AL = operating system version ID (see #01579) Notes: as of Concurrent DOS/XM 5.0 (possibly earlier), the version is stored in the environment variable VER and the OS type in variable OS use this function if you are looking for multiuser capabilities, AX=4452h for single-user this function should never return the single-user values; however, an application should be prepared to accept single-user values, i.e. it should check the returned AH and AL separately CCI Multiuser DOS 7.22 returns AX=DX=1466h. DR DOS 3.31+ error returns with AX=0001h SeeAlso: AX=4452h,AX=4459h (Table 01579) Values for Digital Research operating system version ID: 32h Concurrent PCIBM PC DOS 3.2 41h Concurrent DOS 4.1 50h Concurrent DOS/XM 5.0 or Concurrent DOS/386 1.1 60h Concurrent DOS/XM 6.0 or Concurrent DOS/386 2.0 62h Concurrent DOS/XM 6.2 or Concurrent DOS/386 3.0 66h DR Multiuser DOS 5.1, CCT Multiuser DOS 7.x 67h Concurrent DOS 5.1 SeeAlso: #01581,#04023