Assuming that it takes 2 nsec to copy a byte, how much time does it take to completely rewrite that screen of an 80-character X 25 line text mode memory-mapped screen? What about a 1024 X 768 pixel graphics screen with 24-bit color?

a. 0.04 msec

b. 23.59 msec

Explanation:

a. Text Mode

2 * 80 * 25 = 4000 bytes

1 byte take 2nsec time so, 4000 bytes take

4000 * 10 nsec = 40000 nsec = 0.00004 sec = 0.04 msec

b. Graphics:

24 bit color

3 bytes per pixel

1024 * 768 * 3 = 2 359 296 bytes

2 359 296 * 10 nsec = 23592960 nsec = 0.02359296

sec = 23.59 msec