A video frame displayed onscreen consists of many pixels, with each pixel, or cell,

representing one unit of video output. A video displays resolution is typically specified in

horizontal and vertical pixels (such as 1920 3 1080), and the number of pixels onscreen is

simply the product of these numbers (1920 3 1080 5 2,073,600 pixels). A pixels data con-

tent is one or more unsigned integers. For a black-and-white display, each pixel is a single

number (usually between 0 and 255) representing the intensity of the color white. Color pixel

data is typically represented as one or three unsigned integers. When three numbers are

used, the numbers are usually between 0 and 255, and each number represents the inten-

sity of a primary color (red, green, or blue). When a single number is used, it represents a

predefined color selected from a table (palette) of colors.

Motion video is displayed onscreen by copying frames rapidly to the video display controller.

Because video images or frames require many bytes of storage, theyre usually copied to

the display controller directly from secondary storage. Each video frame is an entire picture,

and its data content, measured in bytes, depends on the resolution at which the image is

displayed and the maximum number of simultaneous colors that can be contained in the

sequence of frames. For example, a single frame at 1920 3 1080 resolution with 256 (28)

simultaneous colors contains 1920 3 1080 3 1 byte 5 2,073,600 bytes of data. Realistic

motion video requires copying and displaying a minimum of 20 frames per second; 24 or

30 frames per second are common professional standards. Using fewer frames per second

results in a jerky motion because the frames arent being displayed quickly enough to fool

the eye and brain into thinking that theyre one continuously changing image.

Assume the computer system being studied contains a bus mastering disk controller and a

video controller that copies data to the video display at least as fast as it can be delivered

over the bus. Further, the system bus can transfer data at a sustained rate of 4 GBps, as

can both the controllers bus interfaces. This system will be used to display motion video on

a monitor capable of resolutions as low as 720 3 480 and as high as 1920 3 1080.

In addition, a single disk drive is attached to the disk controller and has a sustained data

transfer rate of 40 MBps when reading sequentially stored data. The channel connecting

the disk drive to the disk controller has a data transfer rate of 200 MBps. Finally, the files

containing the video frames are uncompressed and stored sequentially on the disk, and

copying these files contents from the disk to the display controller is the only activity the

system performs (no external interrupts, no multitasking, and so forth).

The video display controller contains 4 MB of 10 ns, 8-bit buffer RAM, and the video image

arriving from the bus can be written to the buffer at a rate of 8 bits per 10 ns. The video

displays RAM buffer can be written from the bus while its being read by the display device

(sometimes called dual porting). Finally, data can be received and displayed by the display

device as fast as the video controller can read it from the RAM buffer.

Question 1: What is the maximum number of frames per second (round down to a

whole number) that this system can display in 256 simultaneous colors at a resolution

of 720 3 480?

Question 2: What is the maximum number of frames per second (round down to

a whole number) that this system can display in 65,536 simultaneous colors at a

resolution of 1200 3 1024?

Question 3: What is the maximum number of frames per second (round down to a

whole number) that this system can display in 16,777,216 simultaneous colors at

a resolution of 1920 3 1080?

Question 4: How do the answers to Questions 1 to 3 change if the video files contain

compressed images at an average compression ratio of 10:1. Assume that the CPU is

fast enough to decompress the files as theyre read and deliver the uncompressed con-

tent to the system bus at a rate of at least 500 MBps.