Video displays, also known as monitors, are responsible for displaying the picture that is output by the PC. There are 3 basic types of displays: CRT, LCD, and projection which are discussed in more detail below.
CRT displays were the most common type and were basically just like a traditional television set. They are on their way to obscurity and are being replaced by the newer LCD type of display. CRTs are based on the use of an electronic screen called a cathode ray tube (CRT). The CRT is lined with a phosphorous material that glows when it is struck by a stream of electrons. This material is arranged into an array of millions of tiny cells, usually called dots. At the back of the monitor is a set of electron guns, which produce a controlled stream of electrons. These guns start at the top of the screen and scan very rapidly from left to right. Then, they return to the left-most position one line down and scan again, and repeat this to cover the entire screen. The electron guns are controlled by the video data stream coming into the monitor from the video card which varies the intensity of the electron beam at each position on the screen. This control of the intensity of the electron beam at each dot is what controls the color and brightness of each pixel on the screen. The entire screen is drawn in a fraction of a second.
Color monitors have 3 electron guns that control the display of red, green and blue light. The surface of the CRT is arranged to have these dots placed adjacently in a specific pattern. There are separate video streams for each color coming from the video card, which allows the different colors to have different intensities at each point on the screen. By varying the intensity of the red, green and blue streams, the full gamut of colors is achieved.
The surface of the CRT only glows for a small fraction of a second before beginning to fade. This means that the monitor must redraw the picture many times per second to avoid having the screen flicker as it begins to fade and then is renewed. The speed of this redrawing process is called the "refresh rate".
Display quality depends on the resolution, which is measured as the number of horizontal times the number of vertical pixels. Common resolutions today are 1024x 768, 1280 x 960, 1280 x 1024, and 1600 x 1200. Notice that each of these uses a 4:3 ratio which is known as the aspect ratio. The aspect ratio is different for widescreen and other formats.
Another factor affecting quality is Dot Pitch. Dot Pitch is a measurement of the distance between dots of the same color on the screen. The closer together they are, the smaller the dot pitch and the better the picture. Dot Pitch is measured in millimeters.
Most CRT displays connect to the video adapter via a DB-15 connector on the board. Older video standards utilized a 9 pin connection. Some high performance monitors are connected via a BNC connection.
Liquid Crystal Display (LCD) panels were previously only available for laptops, however, they are now the most common type for PCs as well. Why LCD? They are lighter, thinner, have a better picture, use less than half the power, and do not flicker like their CRT counterparts. As the name would imply, this technology uses a liquid with crystals in it. LCDs have resolution, refresh rates, and the other discussed terms in common with CRTs. Below are a few terms that are specific to LCDs.
Response Rate - This refers to the amount of time it takes for all of the pixels on the screen to go from black to white and back to black.
Contrast Ratio - This is the difference between the lightest and darkest spots that the LCD can display.
Backlighting - LCD monitors are backlit for brightness. The strength of this backlighting affects the overall picture quality.
Unlike analog CRTs, LCDs use a digital signal. The output from a video card is initially digital, but they use a chip called RAMDAC which converts the digital output to analog for use with CRT monitors. Well, what if you are using a LCD monitor? Fortunately, most LCDs are able to convert the analog stream back into digital. In fact, many LCDs offer a DB-15 connector just like their CRT predecessors. With the newer standards found on many video cards and all LCDs, no conversion is necessary. This is thanks to DVI and HDMI (the current standard) connections.
DVI (Digital Visual Interface):
DVI is a video interface standard designed to provide very high visual quality on digital display devices such as flat panel LCD computer displays and digital projectors. DVI can support the current video standard 1080p.
There are 3 types of DVI interfaces as follows:
DVI-D - True Digital Video DVI-D format is used for direct digital connections between source video (namely, video cards) and digital LCD (or rare CRT) monitors. This provides a faster, higher-quality image than with analog, due to the nature of the digital format. All video cards initially produce a digital video signal, which is converted into analog at the VGA output. The analog signal travels to the monitor and is re-converted back into a digital signal. DVI-D eliminates the analog conversion process and improves the connection between source and display.
DVI-A - High-Res Analog DVI-A format is used to carry a DVI signal to an analog display, such as a CRT monitor or an HDTV. Although some signal quality is lost from the digital to analog conversion, it still transmits a higher quality picture than standard VGA.
DVI-I - The Best of Both Worlds DVI-I format is an integrated cable which is capable of transmitting either a digital-to-digital signal or an analog-to-analog signal, but it will not work transmitting a digital-to-analog or analog-to-digital signal.
In addition to the above formats, the DVI interface has 2 additional types: single link and dual link. Dual link has a lot more pins so it offers higher throughput, hence, better resolutions can be supported. Below is a chart of the various DVI types available:
HDMI (High-Definition Multimedia Interface):
HDMI is an audio/video interface for transmitting uncompressed digital data. It is a digital alternative to previous analog standards, such as coaxial cable (RF), composite video, S-Video, component video, VGA, and others. HDMI connects devices such as Blu-ray players, AVCHD camcorders, computers, video game consoles, stereo receivers, computer monitors, digital TVs, and others. HDMI supports 1080p video, 3D video, and 8 channels of 24-bit 192kHz audio. The big advantage of HDMI is that it supports video and sound with one cable and connector unlike DVI which just supports video. The connector is much smaller than DVI's as well. HDMI offers a feature called DDC which is similar to the plug-and-play feature in Windows. Devices can be automatically configured to work with each other without manual configuration. HDMI also supports High-Bandwidth Digital Content Protection (HDCP) which prevents copyright infringing media from playing at full resolution. HDMI is backward compatible with DVI via the use of an adapter.
Projectors, like the ones often used in board rooms and class rooms, project what is showing on the computer screen onto a wall or screen. Just like monitors, there are CRT and LCD projectors. Strangely enough, CRT projectors are typically have a higher quality picture, but they are much larger, heavier, and more expensive. LCD projectors, while lacking high end picture quality are usually portable.
Below are a few terms you might want to know regarding projection displays:
Lumens - This refers to the brighteness of the projector. The number of lumens that is appropriate depends on the size and brightness of the room it will be used in.
Lamps - The lamp is essentially a heavy duty light bulb that produces the light needed by the projector. They do fail and are fairly expensive to replace. The also generate a lot of heat, but the projector will have a fan to cool it.
Throw - This is the size of the image on the wall or screen given a certain distance from it. Projectors have a minimum and maximum throw distance that varies depending on the lens it has.
The video card, also known as the display adapter, is the component that provides communications between the the system board and the display. Video cards are typically an expansion card that is inserted into the motherboard, however, many systems come with onboard video. Typically, onboard video isn't near the quality of a high-end video card so many gamers, graphics professionals, and others choose to add a video card instead.
As with everything else, there have been several different standards over the years with many of them coming in the last couple of years. The table below has more information:
Common for PC displays
Common for PC displays
For fullscreen displays
For widescreen displays
Very large displays
For the largest displays
Video cards contain their own RAM (VRAM) that allows them to support higher levels of color depth, resolution and performance. Unfortunately, the PCI bus which offers a throughput of 132 MBps, was unable to keep up with the increasing demands of newer technologies. The Advanced Graphic Port (AGP) was developed to attain even higher performance levels including 3-D graphics texturing. This was achieved by creating a direct connection to the northbridge on its own bus. AGP is derived from the PCI specification and is only used for video adapters. There are several AGP levels that are listed in the table below:
The multipliers 1x, 2x, 4x and 8x refer to the number of times the signal is increased per clock cycle.
Like AGP, the PCIe interface is also based on the PCI standard, but has speeds much faster than AGP or PCI. In fact, with its theoretical throughput of 16 GBps, it is sure to replace AGP for graphics cards and is already being used for that purpose.
Where you will install a video card depends a lot on what type of video card you have and which slots are available. If the card is AGP, there is only one choice as motherboards only have 1 AGP slot. If installing a PCI or PCIe card, it is good idea to leave the slot on the fan side of the video card blank for ventilation as modern video cards can get pretty hot. Once you have identified the correct slot, simply insert the edge with the metal contacts into the slot making sure not to touch the contacts. Once inserted, screw the card into the case to lock it in and connect the monitor cable to the back of the card. The final step is to install the driver for the video card. This will usually be located on an accompanying disk, however, it is usually better to go download an updated driver from the manufacturer's website which may contain bug fixes and enhancements.
The most common video problem is incorrect settings in the video card properties. When viewing these properties, Windows will often allow you to set the resolution and/or color depth to a level that your monitor can't support (but your video card can). For example, if your monitor only supports a maximum resolution of 1024x768, but you change the properties in Windows to 1280x1024, the screen is most likely going to get garbled, or more likely go blank with static lines. Fortunately, most video cards require a confirmation after the change is made and if it is not confirmed, it will revert to the previous resolution after a short waiting period. If for some reason incorrect settings are made, you can boot into safe mode (more about this in the operating systems section) which uses a VGA display mode (640x480) and you can change the settings back manually.
Another common problem is the installation of an incorrect driver. If you are having video problems, make sure you have the correct and updated driver from the manufacturer. Again, you can use safe mode to uninstall the current driver and install the correct one.
Video cards don't have too many hardware failures. If the card has a fan, it can fail and cause the card to overheat. You can always open the case to make sure the fan is still running. This and other hardware failures will typically result in a garbled screen and possibly lock up the computer. One way to confirm a hardware failure is to use our trusty friend safe mode. If the problem doesn't show up there, it probably isn't a hardware problem and is more likely one of the above.
If you suspect that an onboard video adapter has gone bad, you can insert a video adapter and see if that works. If so, you can replace the motherboard, or just continue running the video off the video card.
You should never attempt to repair a CRT monitor as they can contain electrical charges as high as 30,000 volts - a potentially lethal amount. Most display repairs should be referred to a professional and are not typically part of a hardware technician's job due to the complexity and danger involved. Keep in mind that a large number of repair jobs will cost as much or more than the monitor itself. Typically, when a monitor goes bad, it is replaced.
Your computer's sound card is responsible for taking sound data from a disk (like an MP3 file) and converting it so your computer's speakers can play it. Usually, this tweaking consists of changing digital ones and zeros into analog waveforms your ears can recognize. This process is referred to as sound output.
The sound card is also responsible for doing it the other way around. It takes external sounds such as your voice as you talk into a microphone and converts those waveforms into ones and zeros so that they can be stored on a disk. This process is referred to as sound capture.
Sound cards are internal cards that are either built into the motherboard or are installed in an expansion slot - usually PCI. The back of the sound card contains RCA jacks for connecting speakers and microphones.
When choosing a sound card, you will need to take into account a variety of considerations since not all sound cards are created equal. For example, many sound cards support surround sound and have inputs for multiple speakers. Others provide sub-woofer support, a joystick jack, and possibly other features.
Installation of a sound card is basically the same procedure as described above for a video card. Once the card is installed, you will need to connect an MPC2 cable from the sound card to each of your optical drives (or they won't play sound). In the back of the sound card, plug in your speakers, microphone and any other devices. Install the latest driver from the manufacturer.
Sound on your PC can be in a wide variety of formats, many of them proprietary. The most common are WAV, MP3, and WMA. Let's take a look at a few common formats a little more in depth.
WAV - Once the most common format. WAV files can be very high-quality, but suffer from large file sizes.
MP3 - The MP3 format was developed to remove some of the unnecessary sound data thus creating smaller sized files. This compression has allowed MP3 to become the most common format used today.
MIDI - The Musical Instrument Digital Interface format uses text files that provide a series of instructions to a sound card as to which notes to play on which instruments. The sound when played depends on the capabilities of the sound card. Since this format uses synthesis, it is rarely used for listening to music. In fact, MIDI is not used much anymore except occasionally in games. MIDI files are extremely small.
WMA - Windows Media Audio is a fairly popular format. It is proprietary to Microsoft and plays on the Windows Media Player.
AIFF - The Audio Interchange File Format is common on Macintosh computers and play in QuickTime player.
There are a number of video formats that contain sound and you have to make sure that you have the proper codec installed to support the video and sound. Common formats for video with sound are: AVI, MPEG, MOV, WMV, and DIVX.
Most problems with sound are pretty easy to figure out. If you are having a problem getting sound, check the following items: Make sure that the speakers are on and the volume is turned up high enough on the speakers. On the computer, make sure that volume in Windows is turned up and not muted. Make sure that your speakers are plugged into the correct RCA jack on the sound card. Make sure that you have the correct driver installed. If you aren't getting sound from an optical drive such as a DVD-ROM player, make sure you have the MPC2 cable connected correctly. If particular file formats aren't playing, make sure you have the correct codec's installed and are using a media player that supports the format you are trying to play.