INT 21 - PC Tools v5.x PC-Cache - INSTALLATION CHECK
AH = 2Bh
CX = 4358h ('CX')
Return: AL = FFh if PC-Cache not installed
AL = 00h if installed
CX = 6378h ('cx')
BX = ???
DX = ???

See also: 16FFA5CX1111

212B - PC Tools v5.x PC-Cache - INSTALLATION CHECK