Category : Science and Education
Archive   : PCL54.ZIP
Filename : DISPLSTD.TUT

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DISPLAY STANDARDS - WHY SOME PROGRAMS WON'T RUN!

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All beginners must at some point learn the compatibilities of
software, the monitor and electronic video display circuits
(sometimes called "cards") attached to a computer. Your monitor
is usually matched to a video circuit board within the computer.
You can change the monitor and video circuit board to add color
or upgrade to higher resolution color as you wish. The computer
remains the same but the visual clarity changes!

Many software packages allow several types of display in color
or monochrome with varying degrees of resolution. These types of
displays are listed below. Remember: both the monitor and the
video card within the computer determine the type of color (or

lack thereof) which you see. Color quality can be changed by
buying a different monitor and replaceable video circuit board.

MONOCHROME of MDA refers to text (characters, letters and numbers)
on the monitor screen. A monochrome screen is typically
manufactured to produce green or amber letters on a dark field.
A monochrome monitor is usually mated to a monochrome circuit
board (card) inside the computer. MDA was the first IBM graphics
display standard and supports older software packages but is
not considered a modern standard for today's software needs.
It is of basic utility for older office software - perhaps word
processing and accounting use. Also known as the MDA (monochrome
display adapater.) Resolution or clarity of the image is fairly
low with a structure of glowing dots making up the image. 720 dots
accross the width of the screen by 350 vertically. Also known as
720 x 350 resolution.

HERCULES is a reference to a higher resolution monochrome circuit
board or card. Hercules circuits usually drive or operate a
monochrome monitor. By itself a Hercules circuit card CANNOT
drive a monochrome monitor when you try to run a COLOR software
package. Low priced computers frequently have Hercules display
resolution and may have trouble displaying color games or
graphics software which try to output color on the monochrome
Hercules circuit. Result: no display. Solution: obtain alternate
software or purchase a true color monitor and color video
circuit for the computer. Some models (Hercules Incolor card)
offer up to 720 x 348 dot resolution. A fair choice for office
use where a color display is not necessary. Hercules display
resolution is an affordable compromise for a low end PC for a
fair variety of office or home use software where color is not
needed.

CGA (color graphics adapter) refers to the first IBM low resolution
color display. Color monitors and CGA circuit boards (cards) are
usually mated together in this scheme. Alternatively, CGA color
circuits can operate a monochrome monitor, but results can be
unpredictable depending on the software program. Some color
software programs produce faint or flickering images when a CGA
color circuit operates a monochrome monitor. Of course, when a
CGA circuit card operates a monochrome monitor, only black and
white images can be seen. 640 x 200 dot resolution. CGA was the
first color display adapter for the PC and is fairly primitive.
Many games and good quality software packages exist for CGA
display and it is of fair quality for light office use.

EGA (enhanced graphics adapter) is high resolution color display
circuit. The EGA card typically operates or drives a special
high resolution EGA monitor or "multisync" monitor. Many
software packages support EGA. Is is a popular, although not
very modern display standard. Up to 350 x 720 dot resolution.
Most modern packages still support EGA display resolution.
A reasonable alternative for cost conscious computing in a wide
variety of home or office settings.

VGA has still higher resolution and requires a still higher
performance monitor. VGA color monitors are somewhat expensive,
but owners can opt for a VGA monochrome monitor screen which is
quite affordable if high resolution is desired, but color is not
necessary. VGA resolution is considered a "modern standard" for
today's software and hardware in either a home or office
setting. VGA is preferred by most users for its ability to run
almost all software packages, including older CGA, EGA and
monochrome software!

XGA is the newest emerging video display standard for IBM
compatible computers. The majority of software packages do
not, as yet, completely support this high fidelity color image.

Curiously most display schemes are "downward compatible". This
means that a high end VGA card can, through software command, be
switched downwards into EGA and even CGA or Hercules modes.
Ponder this for a moment: if you own a high end VGA or EGA
display system you can "downshift" to display CGA and possibly
Hercules monochrome resolution. This is helpful when the
software you are using will only display up to CGA resolution,
for example. Many utilities are available to help you set the
color spectrum and output quality of EGA and VGA display
circuits. And there are other standards even beyond VGA display
resolution, of course.

The bottom line: most low end PC compatibles contain circuits
for monochrome and frequently either CGA or HERCULES resolution.
Modern computers contain VGA displays which is considered
today's modern "gold standard."

Some computers contain circuits for only CGA. The trick is to
determine what display standard you have and use software which
will work with that display resolution. Of course you can always
upgrade to a higher standard later by swapping both the monitor
and display card. Ask your computer salesperson what type of
graphics adapter or display system your computer contains.

Owners of CGA (color) circuit board computers who have only a
monochrome monitor can sometimes improve software display by 1)
slightly increasing screen brightness with the monitor
light/dark control but be careful! 2) using the DOS mode setting
to switch the CGA circuit board to its black and white output
(example: mode bw80). 3) Searching the software instructions for
resetting the software package itself to display in other color
shades which can be seen clearly on the monochrome monitor.

Owners of older hercules circuit boards who wish to use CGA or
color software can try loading and running several small software
emulation programs which try to help a Hercules or monochrome
display card work in CGA color mode. This is a "poor man's"
solution or "workaround" which let's you display color software
on your Hercules or monochrome monitor!

Of course you will only see shades of gray, but at least the
software can display on the screen. Examples of these types of
emulation programs for Hercules cards include the shareware
program SIMCGA.COM and CGA.COM. Some slight screen flicker may
be apparent when using these CGA emulation programs, but this is
an inexpensive way to help a monochrome hercules circuit display
the many color software programs on a monochrome monitor. CGA
software usually consists of games and some color graphics
programs which won't display or display poorly on your
monochrome monitor. The idea is that sometimes inexpensive
emulation software can "patch" or make up for a lack of display
hardware.

If you wish, you can purchase additional plug in circuit boards
to "upgrade" your computer to these ever higher standards of
display clarity. Example: CGA circuit owners can add an EGA
circuit card which displays EGA, CGA and Hercules modes. For the
most part monochrome is satisfactory for office use, Hercules is
adequate if you need to do graphing, CGA is useful for games and
other types of color graphing. Some computers are equipped with
several circuits built in (monochrome, hercules and CGA) but you
need another monitor to use all the circuits! Some owners find
that their computer contains an EGA card, for example but they
only have a simple monochrome monitor. The upgrade path here is
simply to replace the monitor to allow the higher resolution
modes contained within the circuit card to be displayed.

Final thought for the bewildered beginner: find out from your
instruction book or computer salesperson which video circuits
(CGA, Hercules, etc) are contained in your computer. Determine
which type of monitor you have. Finally check software purchases
to be sure the software package will match or mate to your
equipment and display properly. Consider purchase of an
additional display circuit card if the software you need or use
does not display with your computer. In most cases, set
priorities. If you use the machine mostly for office use,
monochrome or Hercules text mode is fine. For more sophisticated
design, graphics or use with games, color adds clarity.

One the contemporary computer scene, a minimum for today's modern
software is at least EGA color circuit and appropriately matched
EGA color monitor.