• Display adapters, Video adapter or Video card or Graphics card is a plug-in card in a desktop computer that performs graphics processing. It is also known as a display card or graphics adapter. Modern display adapters use the PCI Express interface, while earlier cards were using PCI and AGP.
• The maximum resolution supported by the system, refresh rate and the number of colours displayed on the screen – all depend on the video adapter used in the monitor.
• A monochrome monitor cannot display color no matter how powerful the video adapter.
• Nowadays the graphics circuits are built into the chipset on the motherboard, and a separate plug-in card is not required in such cases.
• Various graphics adapter cards are available in the market like CGA, VGA, IBM. Each adapter offers several different video modes.

In windows, we can find the information about the display adapter in the system information as shown in the following figure.

Characteristics of Display Adapters

Maximum Resolution: Resolution is defined as the total number of pixels that can be displayed without overlapping on the monitor screen. Sometimes it is expressed by the number of dots in the horizontal direction by the number of dots in the vertical direction. Higher resolution gives better visualization of the scene. Commonly used resolutions are 640 x 480, 800 x 600, 1024 x 768 and 1280 x 1024. Screen resolution decides the size of the frame buffer.

Color depth: Color depth is defined by the number of bits used to represent the colour. The size of the frame buffer also depends on the number of colours supported by the system. A system using n bit per pixel can support a maximum 2ⁿ different colors.

 A system with a resolution of 800 x 600, which supports a true color system (24 bit/pixel) needs (800 x 600 x 24) / (8 x 1024 x 1024) = 1.37 MB memory for the frame buffer. A system with the same resolution which supports 256 colors requires
(800 x 600 x 8) / (8 x 1024 x 1024) = 0.458 MB memory for frame buffer.

Refresh rate: Refresh rate defines how many number of the screen can be painted in 1 second. The normal refresh rate in raster CRT monitors and color TV sets is 60 Hz. A lower refresh rate may produce a flickering effect. Different adapter cards may support multiple resolutions with the same or different colors. For example, VGA supports 640 x 200, 640 x 350 and 640 x 480 with 16 color support for each mode.

TV Tuner: A card with a built-in TV tuner can turn a PC into a TV set. We can use a traditional antenna or connect the card to a cable or satellite system.

Accelerator: A graphics accelerator is a special type of video adapter that contains its own processor to boost performance. Graphics rendering is the responsibility of the accelerator. They are specialized to do such tasks and so they are much better than the general purpose CPU. CPU doesn’t need to render the graphics at all, so they can focus on executing other commands.

Example:

If 8 bits per pixel, per color scheme, is used for an RGB display device, how much memory is required to hold picture data worth one screen, if the resolution is 800 x 600. If the refresh rate is 50Hz, how much memory is required to hold picture data for a duration of one second?

Solution:

Total number of pixel = Screen resolution = 800  x 600 = 4, 80, 000 pixels

Each pixel takes 8 bits to represent the color, so the total number of bits required to store display information
 = 4, 80, 000  x 8 = 38, 40, 000 bits

Size of frame buffer in Byte = 38, 40, 000 / 8 = 4, 80, 000 Bytes

Size of frame buffer in KB = 4, 80, 000 / 1024 = 468.75 KB

Size of frame buffer in MB = 468.75 / 1024 = 0.46 MB

To store the picture information of resolution 800 ´ 600 pixels having 8 bits per pixel, 0.46 MB memory is required.

The refresh rate is 50 Hz, so it paints the screen 50 times in a second. On every cycle, new data is loaded in the same buffer. So, the size of the frame buffer does not alter, it is just reloaded 50 times in a second.

Example:

Assume that certain true color system supports a resolution of 1200 x 1024 pixels. Determine the size of the frame buffer for the system.

Solution:

The true color system uses 24 bit/pixel to represent the color.

Total number of pixel = Screen resolution = 1200 ´ 1024 = 12,28,800 pixels

Each pixel takes 24 bit to represent the color, so the total number of bits required to store display information
= 12,28,800 x 24 = 2, 94, 91, 200 bits

Size of frame buffer in Byte = 2, 94, 91, 200 / 8 = 36,86,400 Bytes

Size of frame buffer in KB = 36,86,400 / 1024 = 3,600 KB

Size of frame buffer in MB = 3,600 / 1024 = 3.5156 MB

Example:

How much time is required to scan individual pixel during screen refresh on a raster system with resolution 600 x 400 and refresh rate of 60 Hz. (Assume horizontal and vertical retrace time is negligible).

Solution:

Total number of pixels = Screen resolution = 600 x 400 = 2,40,000

Refresh rate = 60 Hz, so 2, 40,000 pixels are accessed 60 times per second.

So number of pixels accessed in one second = 2, 40,000 x 60 = 1,44,00,000.

So the time required to access individual pixels = 1 / 1,44,00,000 = 0.0694 microseconds.

Example:

How much time is spent in scanning each pixel, each row and each column during screen refresh on a system with resolution 300 x 200 and a refresh rate of 60 frames per second? (Assume horizontal and vertical retrace time is negligible).

Solution:

Total number of pixels = Screen resolution = 300 x 200 = 60, 000

Refresh rate = 60 Hz, so 60, 000 pixels are accessed 60 times per second. So number of pixels accessed in one second = 60, 000 x 60 = 36, 00, 000

So time required to access individual pixel = 1 / 36,00,000 = 0.277 microsecond

Each row contains 300 pixels,

So time required to access one row = 300 x 0.277 = 83.1 microsecond

Each column contains 200 pixels,

So time required to access one column = 200 x 0.277 = 55.4 microsecond

Example:

If the transfer rate of the system is 10⁴ bits/second, what amount of time is required to load a frame buffer of size 400 x 300 which supports 256 colors?

Solution:

As the system supports 256 colors, each pixel in the frame buffer needs 8 bits to represent color.

So, the Time required to load buffer  =  (Total Number of pixels) / (Transfer rate) = (400 x 300 x 7) / (10⁴)  = 96 second

Example:

What is the fraction of the total time per frame spent in the retrace of an electron beam for a non-interlaced raster system with a resolution of 600 x 400, a refresh rate of 60 Hz, a horizontal retrace time of 5 microseconds and a vertical retrace time of 500 microseconds?

Solution:

Here, number of rows are 400.

The refresh rate is 60 Hz, so one frame is scanned in 1/60 = 16.67 microseconds

Refresh time per frame = (Number of rows x Horizontal retrace time) + Vertical retrace time             

=   (400 x 5) + 500

= 2.5 microsecond

Fraction of total time per frame spent in retrace = (2.5 microsecond) / (16.67 microsecond) = 0.15 = 15 %

Example:

If a true color display system has 300 scan lines and an aspect ratio of 3:4, how many bits per second are required to show 60 frames per second?

Solution:

Number of scan lines = 300. So number of pixels in one column is 300.

Number of pixel in each scan line = (300 x 4) / 3 = 400

So, the screen resolution is 400 x 300.

A true color system needs 24 bits per pixel to represent color.

So, size of frame buffer = 400 x 300 x 24 = 28, 80, 000 bits = 2.88 x 10⁶ bits

The refresh rate is 60 Hz, so 2.88 x 10⁶ bits are displayed 60 times in one second

So, the number of bits required per second = 2.88 x 10⁶ x 60 

= 1.728 x 10⁸

1.728 bits per second are required to show 60 frames per second

Example:

How long would it take to load a 1280 by 1024 frame buffer with 12 bits per pixel if transfer rate is 1Mbps?

Solution:

Each pixel in the frame buffer takes 12 bits to represent color.

So, the Time required to load buffer  = (Total number of pixels) / (Transfer rate)

= (1280 x 1024 x 12) / (1024 x 1024)

= 15 second

Example:

How long it would take to load a 640 by 400 frame buffer with 12 bits per pixel, If 10⁶ bits can be transferred per second?

Solution:

Each pixel in frame buffer takes 12 bits to represent color.

So, the Time required to load buffer  = (Total number of pixels) / (Transfer rate)

= (640 x 400 x 12) / (10⁶)

= 3.07 second

Example:

How long would it take to load a 640 by 480 frame buffer with 12 bits per pixel if transfer rate is 1Mbps? What is the size of the frame buffer? How many colors does it support?

Solution:

Each pixel in the frame buffer takes 12 bits to represent color.

So, the Time required to load buffer  = (Total number of pixels) / (Transfer rate)

= (640 x 4800 x 12) / (1024 x 1024)

= 3.52 second

Total number of pixel = Screen resolution = 640 x 480 = 3,07,200 pixels

Each pixel takes 12 bits to represent the color.

So the total number of bits required to store display information = 3,07,200 x 12 =  36,86,400 bits

Size of frame buffer in Byte = 36,86,400 / 8 = 4,60,800 Bytes

Size of frame buffer in KB = 4,60,800 / 1024 = 450 KB            

Size of frame buffer in MB = 450 / 1024 = 0.4395 MB

Frame buffer uses 12 bits per pixels, so supported colors = 2¹²  = 4096 colors

Example:

Consider a raster system with resolution of 1280 by 1024. What size of frame buffer is needed for given system to store 24bits per pixel? How many colors are possible in given system? What is the access time per pixel if refreshing rate is 60 frames per second?

Solution:

Total number of pixel = Screen resolution = 1280 x 1024 = 13,10,720 pixels

Frame buffer requires 24 bits to represent the color.

So, total number of bits required to store display information = 13,10,720 x 24  = 3,14,57,280 bits

Size of frame buffer in Byte = 3,14,57,280 / 8 = 39,32,160 Bytes

Size of frame buffer in KB = 39,32,160 / 1024 = 3840 KB

Size of frame buffer in MB = 3840 / 1024 = 3.75 MB

Frame buffer uses 24 bits per pixels, so supported colors = 2²⁴  = Nearly 17 million colors

Here refresh rate is 60 Hz, so 1280 x 1024 = 13,10,720 pixels are accessed 60 times per second.

So number of pixels accessed in one second = 13,10,720 x 60 = 7,86,43,200    

Time required to access individual pixel = 1 / 7,86,43,200 = 1.27 x 10^-8 Second

Example:

Consider a raster system with a resolution of 1024 x 768. What is the time required to load the raster if 1,00,000 bytes can be transferred per second?

Solution:

Number of pixels = Screen resolution = 1024 x 768 = 7, 86, 432 pixels

1 Byte is required to represent 1 pixel (Considering gray scale display system),

So number of bytes = 7, 86, 432.

1,00, 000 bytes can be transferred per second, so time required to load the raster

=  786432 / 100000

= 7.86 Sec

Example:

If 8 bit per pixel, per color scheme is used for a RGB display device, how much memory is required to hold picture data worth one screen, if the resolution is 800 x 600. If the refresh rate is 50Hz, how much memory is required to hold picture data for duration of one sec.

Solution:

Total number of pixel = Screen resolution = 800  x  600 = 4, 80, 000 pixels

Each pixel takes 8 bit to represent the color, so total number of bits required to store display information = 4, 80, 000  x  8

= 38, 40, 000 bits

Size of frame buffer in Byte = 38, 40, 000 / 8 = 4, 80, 000 Bytes

Size of frame buffer in KB = 4, 80, 000 / 1024 = 468.75 KB

Size of frame buffer in MB = 468.75 / 1024 = 0.46 MB

To store the picture information of resolution 800 x 600 pixels having 8 bit per pixel, 0.46 MB memory is required.

Refresh rate is 50 Hz, so it paints the screen 50 times in a second. On every cycle, new data is loaded in same buffer. So size of frame buffer do not alter, it is just reloaded 50 times in a second.