VGA = (Video Graphics Array)  The minimum standard for PC video display,
which originated with IBM's PS/2 models in 1987.  It supports earlier CGA
and EGA modes and requires an analog monitor.  VGA was initially 640x480
pixels with 16 colors, but non-IBM vendors quickly boosted resolution and
colors to so-called "Super VGA," which was later standardized by VESA.  All
VGA display adapters today start at 256 colors.

SVGA =(Super VGA)  A screen resolution of 800x600 pixels. Third-party
vendors extended IBM's VGA display standard and were the first to use the
term.  SVGA has also referred to 1024x768 resolutions.

XGA = (EXtended Graphics Array)   A screen resolution of 1024x768
pixels.  The term stems from IBM's XGA display standard introduced  around
1990, which extended VGA to 132-column text and interlaced 1024x768x256
resolution.  XGA-2 later added non-interlaced 1024x768x64K.

   Interlacing provides a way of displaying more information on screen
using a less-sophisticated circuit, but at a penalty of producing an
annoying flutter visible on small elements such as icons and buttons.  It
is less noticeable with motion than a still image, which is why traditional
analog television, which uses an interlaced signal, is fine until you have
to read still text (see NTSC).

   Today, most computer displays are non-interlaced.  However, earlier
displays were often interlaced at the highest resolution.. For example,
640x480 and 800x600 might be non-interlaced, but 1024x768 was
interlaced.  I have a old 14 inch Higachi that is non interlaced above 800
X 600.

   A related issue is the vertical scan frequency, or the number of times
the entire screen is refreshed per second.  For a solid image, 70 times per
second (70 Hz) is required.  The higher the refresh rate, the more pixels
have to be redisplayed each second.  Most monitors are not designed for the
highest resolution working with the highest refresh rate, so there is
typically a compromise.  The higher the resolution, the lower the refresh
rate.  The combination of interlacing and low refresh rate can produce
headaches and eye strain.As a general rule a refresh rate of 75 Hz is good
and above 85 is not really necessary. Of course this isn't just up to your
monitor...you video card must support high resolutions, colors and refresh
rates.

Color depth or pixel depth is the bit depth that determines the number of
colors that can be displayed at one time.  Digital video requires at least
15 bits, while 24 bits produces photo realistic colors.

Color depth   Number of colors
      4-bits       16
      8-bits       256
     15-bits       32,768
     16-bits       65,536
     24-bits       16,777,216
     32-bits       16,777,216 + alpha channel

One other consideration when selecting a monitor is dot pitch  Dot Pitch is
the distance between a red (or green or blue) dot and the closest red (or
green or blue) dot on a color monitor (typically from .28 to .51mm; large
presentation monitors may go up to 1.0mm).  The smaller the dot pitch, the
crisper the image.  A .28 dot pitch means dots are 28/100ths of a
millimeter apart.  A dot pitch of .31 or less provides a sharp image,
especially on text.  Modern monitors all pretty much have a low dot pitch
and this spec is less important then it use to be .....refresh rate is the
important one in monitor selection.

m


>Would someone explain the different video standards (VGA, SVGA, XGA & etc)
>in terms of screen resolution and color depth
>
>Jordan Freedman
>
>

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