Compatibility: 5.0+
Expects: AX    ad80H
Returns: BX    0000H is KEYB.COM is not loaded
version:  BH is major version number (e.g 03H for 3.10)
BL is minor version number (e.g 0aH for 3.10)
Info: Determines whether KEYB.COM has been executed and is resident in
memory and returns the version number.

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INT 2fH ad80H: Is KEYB.COM Installed? / Get Version