The CRT (Cathode-ray tube)
is the most common type of monitor in use. Most CRT monitors
today have three electron guns in the back, one for red, one
for green and one for blue. These guns shoot electric beams
on the inside of the display screen on a phosphor coating
to light up RGB dots that produce a pattern of pixels. In
other words, a beam of light moves across the back of the
screen and produces and image on the screen.
CRT monitors are high-power devices and should
be handled with care, you should never open the cover unless
you are a trained technician and you know what you are doing.
If you are a technician and you open a CRT, make sure to remove
your anti-static wrist strap or the capacitor could use you
as a human conductor of electricity. Some CRTs can hold their
charge for days.
CRT’s connect to you computer with
the DB 15-pin male connector on the cable, and the DB 15-pin
connector on the video adapter.
LCD or Liquid Crystal Display
screens are usually found on laptops, but are becoming popular
as flat panel monitors. LCD technology requires two sheets
of a polarizing material to have a liquid crystal solution
between them. As electrical currents pass through the liquid,
the crystals align which blocks light from passing through.
There are two types of LCD screens. Passive
matrix is less expensive and doesn’t provide sharp graphical
images. The second type, TFT (Thin Film Transistor) is also
known as Active Matrix and is more expensive, but produces
very sharp images comparable to the images on a CRT.
An LCD screen can either connect to your
computer through standard DB 15-pin connectors, or through
USB. LCD’s also have 12V AC external power supplies.
Touch Screen monitors look like any other
monitor but they have a transparent panel around them that
is sensitive to touch. With a touch screen monitor you can
just point to an area on the screen, thus eliminating the
need for a mouse. In most instances, touch screen monitors
are really not that useful, as it is hard to touch very small
areas, however, there are businesses that use them successfully.
Video adapters have been made for all of
the common I/O buses, but the ones CompTIA wants you to know
about for the A+ exams, are the PCI and AGP buses.
PCI or Peripheral Component Interconnect
video adapters were introduced in 1993 and are generally only
32-bits wide. PCI video cards are good, but not good enough
for higher end graphics and 3D graphics.
AGP or Accelerated Graphics Port
video adapters are much faster than PCI cards, and can handle
higher end graphics and 3D graphics. The AGP bus was created
specifically for video, and it provides a direct connection
between the AGP video card and the CPU. AGP video adapters
are available in both 32-bit and 64-bit sizes. AGP comes in
2x, 4x and 8x modes. Each of these modes has a different voltage.
The 2x/4x/8x is the data transfer speed. An 8x motherboard
can take a 4x card, as long as the voltages match. Motherboards
can handle the different voltages; so the manufacturer determines
which voltages will be work. It is best to ignore the 2x,
4x and 8x when shopping for a video card, and pay more attention
to the voltages that your Motherboard can handle.
The voltages for the AGP modes are as follows:
1X/2X = AGP1.0 Spec = 3.3V
2X/4X = AGP2.0 Spec = 1.5V
4X/8X = AGP3.0 Spec = 0.8V
Screen resolution is the number of horizontal
pixels multiplied by the number of vertical pixels on your
screen. For instance if your screen resolution is set at 1024x768,
it means you have 1024 horizontal pixels and 768 vertical
pixels. You can change your screen resolution through the
display properties dialogue box, by right-clicking on your
desktop and choosing Properties from the short-cut menu.
Pixels are made up of a triad of phosphors.
A triad is made up of one red, one green, and one blue phosphor.
Each trial of phosphors equals one pixel.
The refresh rate is the speed at which the
electron guns sweep across your screen. Basically, electron
guns begin sweeping horizontally across your screen from the
upper left corner energizing the phosphors and pixels and
finishes in the lower right corner. The horizontal refresh
rate is defined as the rate at which the electron gun sweeps
across the screen. The vertical refresh rate is the speed
at which an entire screen is swept and the electron guns return
to the upper left corner. Refresh rates are measured in Hertz
The dot pitch of the screen is the distance
(measured in millimeters) between two same colored phosphorus
Interlacing is generally used in lower-end
monitors. In monitors with interlacing, the monitor refreshes
alternate lines of pixels and thus it takes two sweeps to
produce one image.
Color depth is basically the number of distinct
colors that can be represented through your video adapter,
and refers to the number of bits used for each pixel. For
example, if you have a 32-bit video adapter, your video adapter
has a color depth of 32-bits.
|| Resolution and Color
||320 x 200 with 4 colors
640 x 200 with 2 colors
||640 x 350 with 16 colors
from a palette of 64 colors (text mode)
640 x 200 with 2 colors (graphics mode)
||640 x 480
||640 x 480, 800 x 600,
1024x 768 and higher with X colors from a palette of 16.7
depends on the amount of video ram, ranges from 256 -
To determine whether or not your memory card
can handle a particular resolution use the following calculation:
horizontal resolution X vertical resolution X color depth,
divided by 8,388,608.
VIDEO BIOS SETTINGS
There are several video BIOS settings, however
most are not in use today.
This video BIOS setting used to tell your
BIOS what type of video card you had in your system, and how
to talk to it. The default setting was generally EGA/VGA.
This setting is of no use today, and is ignored by your system
regardless of how you set it.
Init Display First
The Init Display First BIOS setting is used
for systems with more than one monitor. If you have more than
one monitor on your system, it lets you decide whether you
want the AGP or the PCI monitor to start up at boot. This
setting is also used by Windows 9x and up to set the primary
Assign IRQ for VGA
Most video cards don’t require an IRQ,
and thus in most cases this setting is useless. This setting
lets you decide whether or not you need an IRQ for your video
card. You generally don’t have to worry about this setting
– if you have a video card that needs an IRQ you’ll
know because your system will freeze up.
VGA Pallet Snoop
VGA Pallet Snoop is an old setting that is
no longer in use. It used to open a PCI video cards pallet
so that other devices could read or change the palette.
Video Shadowing Enabled
The Video Shadowing Enabled setting is outdated
and no longer in use. This setting used to let you shadow
video ROM. Today this setting is ignored because most video
cards are capable of performing video shadowing themselves.
Many different types of RAM are used or have
been used on video adapters. Some even use plain EDO RAM,
but most video adapters come with special video RAM used to
optimize video performance. More video RAM allows for more
colors and a higher resolution to be displayed.
Video RAM constantly updates in order to
show ever change that takes place on your screen. CompTIA
wants you to know about the VRAM, WRAM, and SGRAM types of
Video RAM for the A+ certification exams.
VRAM or Video RAM is dual ported (it can
be read to and written from at the same time). Although VRAM
is fast, it is not as fast as WRAM.
WRAM or Windows Accelerator Card RAM is faster
than VRAM, and thus produces better video than VRAM. WRAM
is also dual ported, meaning it can be both read from and
written to at the same time.
SGRAM or Synchronous Graphic RAM synchronizes
with the CPU bus. SGRAM uses masked writes and blocked writes
in order to increase bandwidth for intensive graphics. SGRAM
is not dual ported, and cannot be read to and written from
at the same time, although it can open two memory pages at
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