Page 97 - DCAP303_MULTIMEDIA_SYSTEMS

Unit 5: Video

9 × 14 pixels. A 40 × 25 text mode was also supported in 16 colours. In both, the foreground notes
and background colours could be changed for each character.

2. Monochrome graphics mode which displayed graphics at 640 × 200 pixels. This was lower
than the Hercules card but seemed to serve the purpose for an initial release and this was
quickly replaced with the EGA standard.
3. Colour graphics mode which came in two flavors: a 320 × 200 pixel mode with four colours
and a lesser-used resolution of 160 × 200 in 16 colours. The four-colour mode only had two
official palettes to choose from:

1. Magenta, cyan, white and background colour (black by default).
2. Red, green, brown/yellow and background colour (black by default).
5.9.4 enhanced Graphics adapter (eGa)

The Enhanced Graphics Adapter was introduced by IBM in 1984 as the primary display
for the new PC-AT Intel 286-based computer. The EGA increased resolution to 640 × 350
pixels in 16 colors. The card itself contained 16 KB of ROM to extend the system BIOS to add
graphics functions. The card started with 64 KB of video memory but later cards and clone
cards came with 256KB of video memory to allow full implementation of all EGA modes
which included:
1. High-resolution mode with 640 × 350 pixel resolution. On any given screen display a total
of 16 colours could be displayed; however, these could be selected from a palette of 64
colors.

2. CGA mode included full 16-color versions of the CGA 640 × 200 and 320 × 200 graphics
modes. The original CGA modes were present in the card but EGA is not 100% hardware-
compatible with CGA.
3. MDA could be supported to some degree. By setting switches on the card an MDA monitor
could be driven by an EGA card however only the 640 × 350 display could be supported.

5.9.5 video Graphics array (vGa)
With VGA you see a change in the terminology from adapter to array. This was a result of
the fact that VGA graphics started to come on the motherboard as a single chip and not as
plug-in adapter boards that took up an expansion slot in the computer. While since replaced
with other standards for general use, VGA’s 640 × 480 remains a sort of lowest common
denominator for all graphics cards. Indeed, even the Windows splash screen logo comes in
at 640 × 480 because it shows before the graphics drivers for higher resolution are loaded
into the system.
The VGA supports both graphics and text modes of operation and can be used to emulate most
(but not all) of the EGA, CGA and MDA modes of operation). The most common VGA graphics
modes include:
1. 640 × 480 in 16 colours. This is a planar mode with four bit planes. When speaking about
VGA, this is the mode most often thought of and is often what is meant when some say
“VGA.”
2. 640 × 350 in 16 colours.
3. 320 × 200 in 16 colours.

4. 320 × 200 in 256 colours (Mode 13h). This is a packed-pixel mode.

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