ITPEC FE Subject A April 2025 Question 15
When it takes 10 ns to copy a byte, which of the following is the approximate time (in ms) to copy the data for a 1024 × 768-pixel graphics screen with 24-bit color? Here, any overhead time for copying can be ignored.
Explanation
24 ms — count the bytes in one screen, then multiply by the time per byte.
- •Pixels: 1024 × 768 = 786,432
- •Bytes per pixel: 24 bits = 3 bytes
- •Screen data: 786,432 × 3 = 2,359,296 bytes
- •Time: 2,359,296 × 10 ns = 23,592,960 ns, about 23.6 ms
23.6 ms is closest to 24.
Answer (c)
Why not others:
- •(b) 23 — truncates 23.6 instead of taking the nearest value, or rounds 1024 down to 1,000 (1,000 × 768 × 3 × 10 ns ≈ 23.0 ms)
- •(a) 22 — would need only about 2.2 million bytes, fewer than the 2.36 million in the screen
- •(d) 25 — above the exact 23.6 ms, which is nearer 24
Key rule: Screen data size = width × height × bytes per pixel; divide the colour depth in bits by 8 first, and use the exact pixel counts when the options are close together.
Computer Component · AI-written, may contain errors
This question comes from an official ITPEC past paper. ITPEC Practice is an independent study tool and is not affiliated with ITPEC. See the official FE past-paper collection or Report an issue.