8 - The BIOS Graphics Interface

Abstract

This chapter discusses the BIOS graphics interface. For a graphics programmer, it is very necessary to study in detail how a monitor works, and especially how the program interfaces to the monitor. That is, how the program lights a pixel in the proper color, how a line is drawn, how the palette is changed, and many other things that are usually taken care of by the compiler. Once the programmer understands how the compiler does these things, he/she can do that by himself/herself, or more importantly, he/she can change how they are done to suit the present circumstance. The first step in understanding what the compiler does when graphics are used is to understand disk operating system (DOS) on a deeper level. Basic input /output system (BIOS) is a set of software routines that resides in read-only memory (ROM) chips that are on the different devices on the computer. Software of this type, which is stored in ROM, and thus, permanently bound to a certain device, is often called firmware. BIOS is in ROM chips that are located on the hardware devices; therefore, when the device is replaced, the BIOS is automatically replaced with it. In this way, when a disk drive is replaced, the BIOS for that disk is also replaced.