Video Display Devices

The display devices used commonly can be classified as below:

· Cathode Ray Tube (CRT) display 

· Liquid Crystal Display (LCD) display 

· Plasma Displays  

Cathode Ray Tube (CRT): CRT display is the most commonly used form of visual displays, through it is getting gradually replaced with LCD and Plasma displays. A computer monitor using CRT display.

In a CRT, an  electron beam sweeps the display screen horizontally, one line at a time, gradually down the screen. A synchronization (sync) signal brings the beam back to the top row of the display. This type of scanning (line-by-line) is known as raster scan.

Figure: CRT cross sectional diagram showing important components of a CRT.

There are two types of cathode ray displays. One is non-interlaced, and the other is interlaced. Normally, all the displays are interlaced to reduce flicker.

As shown in the figure, for non-interlaced display, the scanning is done continuously from top to bottom. For non-interlaced display, alternate rows are scanned. A black and white monitor contains only one electron gun, whereas a color display monitor will have three electron guns, each of which represent red, green, and blue. The horizontal and vertical deflection takes place by applying appropriate voltages to the horizontal, and vertical deflection plates. Usually, the screen is refreshed between 60-100 times per second. 

The grid shown in the figure controls the speed with with the electrons hit the screen. If a positive voltage is applied to the screen grid, because of which the electrons are accelerated and hit the screen, making the screen brighter. If a negative voltage is applied to the grip, the electrons are decelerated and the screen will not glow. The microscopic control of electron beam flow, produces images on the screen. One basic unit of measurement is "pixel". A pixel is the smallest area in a graphics display that can be manipulated. 

Given below are the commonly used screen resolutions:

• Display Type Number of pixels    
• Video Graphics Array (VGA) 640 * 480 pixels    
• Super Video Graphics Array(SVGA) 800 * 600 pixels    
• eXtended Graphics Array (XGA) 1024 * 768 pixels    
• Super eXtended graphics Array (SXGA) 1280 * 1024 pixels  
• Screen resolution is always stated as the horizontal number of pixels by the vertical number of pixels. A screen displaying 800 x 600 pixels has 600 rows, each 800 pixels wide.

Graphics Cards: The graphics card resides in the CPU box, and drives the video display. A typical graphics card is shown below:

The graphics card shown includes DVI connector, TV/Video connector, and a VGA connector. The card has an on-board graphics processor with cooling fan. Usually, for graphic intensive applications, you need a higher end graphic adapter card. For normal desktop usage, a video adapter will be sufficient.

PCM CIA Interface Cards (PC Cards)

PCMCIA stands for Personal Computer Memory Card International Association. PCMCIA standards were developed for small, credit card-sized devices, called PC Cards. Though PCMCIA cards (PC Cards) were originally developed for use with Notebook computers, the same are being extensively used in other devices also. 

3 types of PC Cards.

• Type-I :- Type-I PC Cards are typically used for memory devices such as RAM, Flash,  and SRAM cards.
• Type-II :- Type II PC Cards are typically used for I/O devices such as modems, and LAN cards.
• Type-III :- Type III PC Cards are used for devices that consist of thicker components, such as rotating mass storage devices.  

Important characteristics of PC Cards:

Property // Value   

Physical Interface Connector :- 68 pins   

Length :- 85.6 mm   

Width :- 54.0 mm   

Thickness   

Type-I :- 3.3 mm   

Type-II :- 5.0 mm   

Type-III :- 10.5 mm   

Back-end I/O Connector Depends on the functionality of the PC Card  

PCMCIA Card (PC Card) slots: Just like PC Cards, PCMCIA slots also come in three sizes:

Type I slot: Holds up to one Type I card

Type II slot: Holds up to one Type II card or two Type I cards

Type III slot: Holds up to one Type III card or a Type I and Type II card.

Advantages of PC Cards: 

Several advantages offered by PC cards are as given below:

1. CardBus: CardBus allows PC Cards and hosts to use 32-bit bus mastering.

2. DMA: The Standard allows cards to utilize Direct Memory Access technology directly in the hardware when matched with a corresponding host system.

3. eXecute In Place (XIP): XIP allows operating system and application software to run directly from the PC Card. This in turn improves performance, and eliminates the need for large amounts of system RAM.

4. Low Voltage Operation: The Standard enables 3.3V as well as 5V operation. 

5. Plug and Play: PC Cards can be inserted or removed while the system is powered-on.

6. Power Management: The Standard provides a means to interface to APM (Advanced Power Management).

PC Card Uses:

Some of the frequently used PC Card types include the following:

· LAN card 

· Wireless LAN card 

· Modem card 

· ATA flash disk card 

· IEEE 1394/Firewire 

· USB 

A wireless LAN serves the same functionality of a traditional LAN card, but operates without being physically wired to a network device.  It enables a mobile user to connect to a local area network (LAN) through a wireless connection. IEEE 802.11a, 802.11b, and 802.11g specify the technologies for wireless LANs. 

Linksys 802.11b/g Wireless PC Card :- A wireless LAN card is shown in the figure above. Typical specifications for the same are given below:

• Connection Type: Wireless
• Connector: PCMCIA
• Supported Wireless Standards: 802.11b, 802.11g
• Supported Operating Systems: Windows, 98, ME, 2000, XP