INT 15 UC - OS HOOK - ROM(Read-Only Memory) A memory for program storage which may not be changed by the program as it runs. BIOS(Basic Input/Output System) A set of standardized calls giving low-level access to the hardware. The BIOS is the lowest software layer above the actual hardware and serves to insulate programs (and operating systems) which use it from the details of accessing the hardware directly. TRACING CALLOUT (PS30IBM PS/2 Model 30 and below/286,PS50Z,PS95) AH = C5h AL = interrupt being invoked 01h INT 19 02h INT 14 03h INT 16 04h INT 40 (floppy INT 13) 05h INT 17 06h INT 10 07h INT 12 08h INT 11 09h INT 1A Return: all registers except AX must be preserved Notes: called as the very first action of the indicated ROM(Read-Only Memory) A memory for program storage which may not be changed by the program as it runs. BIOS(Basic Input/Output System) A set of standardized calls giving low-level access to the hardware. The BIOS is the lowest software layer above the actual hardware and serves to insulate programs (and operating systems) which use it from the details of accessing the hardware directly. interrupt handlers on the PS/2IBM PS/2, any model Models 30/286, 50Z, and 95 default handler does nothing and returns CF clear for the above subfunctions, CF set and AH=86h for all other subfunctions value of AX passed to the original interrupt handler is pushed on stack immediately prior to call