raster video controller has an 18-bit DAC and comes equipped with 768K of video RAM. a) What is the maximum display resolution (at 4:3) you can provide in a 256 color mode? b) In a 640 x 400 x 16 color mode, how many pages can be stored? c) How many bytes are required for a lookup table in an 8-page 320 x 200 mode?
Answers
Given:
Video Ram available = 768KB
For (a)
Rows : Columns = 4:3
Total number of colors = 256
For (b)
Color mode = 640 × 400 × 16
For (c)
Mode = 320 x 200
To find:
(a) What is the maximum display resolution (at 4:3) you can provide in a 256 color mode?
(b) In a 640 x 400 x 16 color mode, how many pages can be stored?
(c) How many bytes are required for a lookup table in an 8-page 320 x 200 mode?
Solution:
(a) Video Ram available = 768KB.
Let no of rows = 4x
No of columns = 3x
Total pixels: 4x × 3x = 12x²
Total number of colors = 256, therefore 8 bits are required to represent colors.
For each pixel, 1 byte of information is required for storing color.
Therefore, total space needed = 12x² × 1 Bytes
Total available space = 768 * 1024 Bytes
12x² = 786432
x² = 65536
x = 256
Resolution = 4x × 3x = 1024 × 768
(b) In 640 × 400 × 16 color mode:
resolution = 640 × 400
Total colors available = 16
Bits required for colors = 4
Total pixels = 640 × 400
Bits required for each pixel = 4
Total memory required = 640 × 400 × 4 bits = 640 × 200 bytes
= 128000 Bytes
(c) The size of a lookup table is 2ⁿ × 3m
where m is the number of bits required for storing each of red, blue, and green color value and n is the number of bits available for each pixel in frame buffer.
768 × 1000 = 320 × 200 × n
n = 12
m = 8, 8 bits are used for storing the information about red, blue, and green color at that pixel
Therefore, lookup table size: 2¹² × 8 bits
= 4096 × 8 bits = 4096 Bytes = 4KB