^C^1A VIDEO PRIMER
^Cby:  Joel Ellis Rea

^CPart One:  Introduction and Overview

   One thing which separates most personal computers from minicomputers and
mainframes is that personal computers generally have only one user.  Because of
this they usually generate their own video display rather than use multiple
terminals to handle video.   Video is very important, since video display is
the primary means by which the computer communicates with a user.  Printers are
for permanent hardcopy, not for interaction.  Voice synthesis is still used for
specific applications rather than general input and output.  Machine/human
telepathic interfaces are still hard to find outside of science-fiction
novels.  But the video display is the most important machine-to-human
peripheral device of any personal computer.

   Traditionally video has received short shrift during personal computer
design and marketing.  The Apple had reasonably advanced video for its time,
but the TRS-80 and others simply provided barebones text, sometimes with
limited graphics.  When IBM announced the specifications for the IBM Personal
Computer, it became apparent that video was being ignored again.  The original
IBM-PC could not so much as display a cursor on the screen without a plug-in
video board, and video display adapter boards are still not included in the
system.

   IBM provided only two options:  the Monochrome Display Adapter (MDA) and the
Color Graphics Adapter (CGA).  The MDA displays reasonably sharp text on a then
non-standard, special monochrome monitor.  The CGA displays poor quality, but
colorful, text in addition to mediocre color graphics, on a more standard |CR|AG|9B^1I^N
(|CRed^N, |AGreen^N and |9Blue^N, with ^1Intensity^N) Digital monitor.

   Whatever the reasons, this lack of foresight on IBM's part created a huge
market for third-party video display adapter boards and video monitors to sup-
port them.  Then came the Hercules Monochrome Graphics Board and its many
imitators, the Plantronics ColorPLUS board which acted as an enhanced CGA, the
Tecmar Graphics Master (which probably has more video modes than any other
single board), the 400-scanline boards like Persyst's BOB (Best of Both) and the
Sigma Color 400, etc.

   Finally, IBM got into the act by developing a new board named the Enhanced
Graphics Adapter (EGA) board which provided enhanced graphics on RGBI monitors,
high resolution (but not as high as Hercules) graphics for monochrome monitors,
and near-monochrome-quality (NMQ?) text and highly enhanced graphics on a new
kind of non-standard color monitor.  They of course kept it from being
compatible with any of the third-party boards even though this sacrificed
compatibility with their own MDA and CGA boards.

   Subsequently new third-party EGA-compatible boards appeared, which provided
EGA compatibility along with other features, such as better MDA and CGA
emulation, plus Hercules and even Plantronics support.   Now the market seems
inundated with more video monitors, display boards, etc. than you can shake a
stick at.  Unless you are a video engineer, it seems impossible to make heads
or tails out of all this mess and be able to mix or match boards and monitors
to provide the video capabilities you need.

   This series of articles will form a primer on IBM video capabilities, and
hopefully impart enough information to allow you to make informed choices re-
garding present and future display options.  In part two, we will begin with a
description of the fundamentals of video display.  See you then.