System Bios Usage - IBM XT 5160 Technical Reference

System BIOS Usage
The basic input/output system (BIOS) resides in ROM on the
system board and provides device level control for the major I/O
devices in the system. Additional ROM modules may be located
on option adapters to provide device level control for that option
adapter. (BIOS listings for an option adapter are located in the
Technical Reference Options and Adapters manual.) BIOS
routines enable the assembler language programmer to perform
block (disk and diskette) or character-level I/O operations
without concern for device address and operating characteristics.
System services, such as time-of-day and memory size
determination, are provided by the BIOS.
Note: BIOS listings for both the 256/640 and 64/256
system boards are included in this manual.
The goal is to provide an operational interface to the system and
relieve the programmer of the concern about the characteristics of
hardware devices. The BIOS interface insulates the user from the
hardware, thus allowing new devices to be added to the system,
yet retaining the BIOS level interface to the device. In this
manner, user programs become transparent to hardware
modifications and enhancements.
The IBM Personal Computer Macro Assembler manual and the
IBM Personal Computer Disk Operating System (DOS) manual
provide useful programming information related to this section.
A complete listing of the BIOS is given in this section.
Access to the BIOS is through the 8088 software interrupts.
Each BIOS entry point is available through its own interrupt.
The software interrupts, hex 10 through hex lA, each access a
different BIOS routine. For example, to determine the amount of
memory available in the system,
INT 12U
invokes the BIOS routine for determining memory size and
returns the value to the caller.
System BIOS 5-3