INT 4D - TI Professional PCIBM PC - DISK - NOP AH = 05h Note: on the TI Pro, FORMAT.COM contains direct port I/O commands to perform disk formatting, rather than using the 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.