INT 2fH 4300H: Is HIMEM.SYS (XMS Support) Installed?

                                                         Compatibility: 3.0+ 
 Expects: AX    4300H
 Returns: AL    status: 00H = is not installed
                        80H = is installed
    Info: Checks to see if HIMEM.SYS or compatible XMS provider has been
          loaded in CONFIG.SYS and is resident in memory.

          To access XMS services, use INT 2fH 4310H (get XMM entry address)
          and place FAR calls to the entry address returned by that fn.

          See Extended Memory Specification for info on XMS services.

See Also: INT 2fH 43xxH: HIMEM.SYS Functions
          INT 2fH: Multiplex Interrupt
          DOS Functions