System Bios Usage - IBM 5150 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 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.
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 1 A, each access a
different BIOS routine. For example, to determine the amount of
memory available in the system,
INT 12"
invokes the BIOS routine for determining memory size and
returns the value to the caller.
System BIOS 5-3