Background
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CGA
The first color standard for the MS-DOS PC-style computers was CGA
(Color Graphics Adapter or Color Graphics Array). The CGA standard can
display two colors from a palette of 16 colors at its maximum resolution
of 640 by 200. The output of this card is a TTL digital RGB signal.
PGC
The next standard for color on MS-DOS computers was the IBM PGC
(Professional Graphics Card), which has a 640 by 480 resolution with 256
colors from a palette of 4096. The PGC provides an analog output. This
card gained very little acceptance because EGA, the next standard,
provided better price/performance.
EGA
EGA (Enhanced Graphics Array) provided some backward compatibility with
the CGA standard. The first EGA had a maximum resolution of 640 by 350
with 16 colors from a palette of 64. The current EGA standard (EGA
enhanced) is 640 by 480 with 16 colors. Both EGA standards use a TTL
digital RGB output.
VGA
When the PS/2 computers were introduced, the VGA standard came into
existence. There are three color graphics modes on the VGA (Video
Graphics Array) card: 640 by 480 with two colors, 640 by 480 with 16
colors, and 320 by 200 with 256 colors. The 16- and 256-color modes have
a palette of 262,144 colors. The lower resolution of the 256 colors has
limited its use with commercial software. With the VGA standard, an
analog RGB output is used.
MS-DOS Color
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With the CGA, EGA, EGA enhanced, and VGA, it is possible that each card
may require a different driver to be installed for each of the individual
applications that is run on each computer. It is possible, for example,
for a company with five MS-DOS computers to have five different drivers
for the same program: on System One a CGA card from Manufacturer A, on
System Two an EGA card from Manufacturer B, on System Three an EGA
enhanced card from Manufacturer C, on System Four an EGA enhanced card
from Manufacturer D, and on System Five a VGA card from Manufacturer E.
Each of these systems is running Lotus 1-2-3. For each system to display
the 1-2-3 graphs, each system may need a driver for each individual card.
Each of these systems will most likely be displaying in different
resolutions and with a different number of colors.
Even within one graphics card standard, when moving from one card
manufacturer to another, different drivers may be required for the same
program. Also, within one graphics card standard, some third parties may
have decided to change the rules; that is, 640 by 480 by 16 colors is the
standard in EGA enhanced, but there is a card that uses 800 by 560 by 16
colors.
These resolutions remain constant whether a 9-inch or a 19-inch screen is
used--creating a situation where an application cannot depend on the
screen display to represent any type of "what you see is what you get"
environment. A graphic object that is 2 inches by 2 inches on one screen
may become 4 inches by 4 inches on another screen.
With the wide variety of possible color display devices for the MS-DOS
world, consistency is very difficult to maintain.
Macintosh Color
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On the Macintosh, there is more consistency, even when moving from black
and white graphics to full 32-bit color graphics. Card developers and
software developers need not be concerned about which application or which
video card they are going to work with. Both the hardware companies and
the software companies focus their resources on QuickDraw. A driver for a
particular application is not necessary in the Macintosh environment.
Users needn't be concerned about installing drivers to use a particular
application.
The typical Macintosh screen is 72 pixels per inch. There is a
difference from one screen product to the next--but only a small
difference. This allows for a consistent display. A 2-inch by 2-inch
image remains very, very close to 2 inches by 2 inches from screen to
screen.
If you have a smaller screen, you have fewer pixels; however, the pixels
are very, very close to the size of any other Macintosh screen. This
constant pixel size has been a tremendous benefit for the publishing
market because an image on Macintosh "A" is very close to the same image
on Macintosh "B"-- unlike the MS-DOS world. Since all Macintosh video
cards use the same reference (QuickDraw) for image work, it doesn't matter
who manufactured the video card: the image appears the same.
With 32-Bit QuickDraw now available, the Macintosh can also display
photo-quality images--not available in the CGA, EGA, and VGA environments.
When the graphics environment is enhanced, applications do not need to
undergo major changes to continue to work in the new and enhanced graphics
model. For example, programs that ran in Macintosh 1-bit display
configuration continue to run in the 32-bit display configuration. These
applications may not take advantage of the new environment, but they
generally continue to work without modification.
CGA and EGA cards require a digital RGB display monitor. VGA and
Macintosh can, in many instances, use the same multisync monitors.