HP Vectra Technical Reference Manual page 13

The higher the software level, the more powerful the functions provided by the software.
However, along with this power often comes additional overhead which reduces performance
and flexibility. A system programmer should choose the level of software interface required by
the individual set of design constraints. It is good programming practice to use the highest level
of system software that gets the job done. Some system functions can only be performed on the
highest level, since only system software supports the function. However, other system functions
may be performed at more than one level. Using a lower level such as the ROM BIOS provides
improved speed of execution and additional flexibility. Using ROM BIOS routines may affect
program portability to future HP products, and to other industry standard PC's.
1.2 ROM BIOS
The ROM BIOS provides a powerful set of system functions, allowing application programs full
access to the capabilities of the system while maintaining a hardware-independent interface.
The ROM BIOS allows the programmer or system designer to tailor the system to a specific set of
design constraints. Some of the tailoring methods provided to the programmer are:
• The number of interrupts can logically expand to fit requirements.
• Adapter cards can obtain a limited amount of RAM from the system BIOS without installing
device drivers.
• Applications can expand the features of the keyboard without replacing the industry
standard driver (INT 16H).
• The ROM resident mouse driver system can provide the ability to use various input
peripherals with applications not specifically written for them.
These methods maintain application compatibility with minimal effect on system performance.
4 Introduction