ITPEC FE Subject A April 2025 Question 15
ITPEC FE Subject A April 2025 — Question 15 of 60
Screen data copy time — calculate transfer time for a framebuffer.
Given:
- Screen: 1024 × 768 pixels, 24-bit color
- Copy speed: 10 ns per byte
Step-by-step:
- Total pixels: 1024 × 768 = 786,432
- Bytes per pixel: 24 / 8 = 3
- Total bytes: 786,432 × 3 = 2,359,296
- Total time: 2,359,296 × 10 ns = 23,592,960 ns
- Convert: 23,592,960 / 1,000,000 ≈ 23.6 ms ≈ 24 ms
Why not others:
- (a) 22 — too low, would require fewer bytes
- (b) 23 — rounds down incorrectly; 23.6 is closer to 24
- (d) 25 — significantly overshoots the calculation
Key rule: bits-to-bytes conversion (÷ 8) is a common trap. When the question says "approximate," use standard rounding (≥ 0.5 rounds up).
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