INT 2F U - DOS 3+ CRITICAL ERROR HANDLER - INSTALLATION CHECK
AX = 0500h
Return: AL = 00h not installed, OK to install
01h not installed, can't install
FFh installed
Note:   this set of functions allows a user program to partially or completely
override the default critical error handler's message in COMMAND.COM
SeeAlso: INT 24

See also: 2F05

2F0500 - DOS 3+ CRITICAL ERROR HANDLER - INSTALLATION CHECK