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
To Next Page
Loading...
Need help?
General
