ABSTRACT
This chapter describes the VGA video standard and its programmable elements: the CRT Controller, the Graphics Controller, the Sequencer, the Attribute Controller, and the Digital-to-Analog converter (DAC). It also describes the VGA memory structure.
7.1 The VGA Standard In 1987 IBM introduced two video systems to be furnished as standard components for their PS/2 line. These video systems were named the MCGA (Multi-color Graphics Array) and VGA (Video Graphics Array). MCGA, an under-featured version of VGA, was furnished with the lower-end PS/2 machines Models 25 and 30. VGA was the standard video system for all other PS/2 microcomputers. Subsequently IBM extended VGA to its low-endmodels of the PS/2 line. Later on (August 1990) IBM announced a line of inexpensive home computers (designated as the PS/1 line) equippedwith VGA graphics. Since the MCGA standard was short lived and not very popular it will not be specifically considered in this book. However, because MCGA is a sub-version of VGA, its programming is identical to VGA in those video modes that are common to both systems.
