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CompTIA A+ TechNote: Display



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

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

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.

Refresh Rate

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 (Hz).

Dot Pitch

The dot pitch of the screen is the distance (measured in millimeters) between two same colored phosphorus dots diagonally.


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

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.

Video Mode   Resolution and Color Depth
CGA 320 x 200 with 4 colors
640 x 200 with 2 colors
EGA 640 x 350 with 16 colors from a palette of 64 colors (text mode)
640 x 200 with 2 colors (graphics mode)
VGA 640 x 480
SVGA 640 x 480, 800 x 600, 1024x 768 and higher with X colors from a palette of 16.7 million color.
(X depends on the amount of video ram, ranges from 256 - 16.7 million)

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.


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 display monitor.

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 once.

Take the review quiz for this TechNote

Current related exam objectives for the A+ 2003 exam:

DOMAIN 1. Installation, Configuration, and Upgrading

1.1 Identify the names, purpose, and characteristics, of system modules. Recognize these modules by sight or definition.
Examples of concepts and modules are:
- Display devices

1.2 Identify basic procedures for adding and removing field-replaceable modules for desktop systems. Given a replacement scenario, choose the appropriate sequences.
- Display device
- Input devices
-- Touch screen
- Adapters
-- Video card

1.8 Identify proper procedures for installing and configuring common peripheral devices. Choose the appropriate installation or configuration sequences in given scenarios.
- Monitors

1.9 Identify procedures to optimize PC operations in specific situations. Predict the effects of specific procedures under given scenarios.
- Specialized video cards

DOMAIN 2. Diagnosing and Troubleshooting

2.1 Recognize common problems associated with each module and their symptoms, and identify steps to isolate and troubleshoot the problems. Given a problem situation, interpret the symptoms and infer the most likely cause.

- Display device
- Input devices
-- Touch screen
- Adapters
-- Video card

DOMAIN 3. PC Preventive Maintenance, Safety, and Environmental Issues

3.1 Identify the various types of preventive maintenance measures, products and procedures and when and how to use them.
- Cleaning monitors

3.2 Identify various safety measures and procedures, and when/how to use them.
Content may include the following:
- Potential hazards and proper safety procedures relating to:
-- CRTs

3.3 Identify environmental protection measures and procedures, and when/how to use them.
Content may include the following:
- CRTs

DOMAIN 4. Motherboard/Processors/Memory

4.2 Identify the types of RAM (Random Access Memory), form factors, and operational characteristics. Determine banking and speed requirements under given scenarios.

- Types:
-- VRAM (Video RAM)

4.3 Identify the most popular types of motherboards, their components, and their architecture (bus structures).
Content may include the following:
-- 2X
-- 4X
-- 8X (Pro)

Click here for the complete list of exam objectives.

Discuss this TechNote here Author: Tracey Rosenblath


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