int 25

Int 25 - DOS 1+ - ABSOLUTE DISK READ (except partitions > 32M)
Int 25/CX=FFFFh - DOS 3.31+ - ABSOLUTE DISK READ (32M-2047M hard-disk partition)
Int 25/AX=CDCDh - Stacker - GET DEVICE DRIVER ADDRESS
Int 25/SI=4358h - PC-CACHE.SYS - INSTALLATION CHECK