System Bios; System Bios Usage - IBM 5170 Technical Reference

System BIOS
The basic input/output system (BIOS) resides in ROM on the
system board and provides level control for the major I/O devices
in the system. Additional ROM modules may be placed on option
adapters to provide device level control for that option adapter.
BIOS routines enable the assembler language programmer to
perform block (disk or diskette) or character-level I/O operations
without concern for device address and characteristics. System
services, such as time-of-day and memory size determination, are
provided by the BIOS.
If
the sockets labeled VI7 and V37 on the system board are
empty, additional ROM modules may be placed in these sockets.
During POST a test is made for valid code at this location,
starting at address hex EOOOO and ending at hex EFFFF. More
information about these sockets may be found under "System
Board Additional ROM Modules" later in this section.
The goal of the ROM BIOS is to provide an operational interface
to the system and relieve the programmer of concern about the
characteristics of hardware devices. The BIOS interface protects
the user from the hardware, allowing new devices to be added to
the system, yet retaining the BIOS level interface to the device.
In this manner, hardware modifications and enhancements
become transparent to user programs.
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 later in this section.
System BIOS Usage
Access to BIOS is through program interrupts of the 80286 in the
real mode. Each BIOS entry point is available through its own
,.-., interrupt. For example, to determine the amount of base RAM
available in the system with the 80286 in the real mode, INT I2H
will invoke the BIOS routine for determining the memory size and
return the value to the caller.
System BIOS 5-3