---
title: "Raster display and frame buffer load time"
subject: "Computer Graphics"
chapter: 1
key: "semester_5/computer_graphics:raster-system-load-time"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/raster-system-load-time
site: BCT Engineering
---

# Raster display and frame buffer load time

Computer Graphics · Chapter 1: Introduction and Application

- Asked in: 2074 Chaitra, 6 marks
- Video: [Frame buffer in computer graphics(numerical)](https://www.youtube.com/watch?v=I8MByKWmVes) — IT-TECHIEZ
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/raster-system-load-time
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-1

## Question

What do you understand by raster display technology? Suppose a RGB raster system is to be designed using an 8 inch by 10 inch screen with a resolution of 100 pixels per inch in each direction. How long would it take to load this raster system in frame buffer with 24 bits per pixel, if 10⁵ bits can be transferred per second?

## Short answer

Calculating total bits: 800×1000 pixels × 24 bpp = 19,200,000 bits. Dividing by transfer rate 100,000 bits/s gives loading time = 192 seconds.

## Answer

#### Raster display technology
A **raster display** divides the screen into a rectangular matrix of pixels. The picture is stored as the colour/intensity of every pixel in a memory area called the **frame buffer**. The display controller reads the frame buffer row by row (scan line by scan line) and the electron beam sweeps across the screen from left to right and top to bottom, lighting each pixel with the stored intensity. After the last line, the beam returns to the top (vertical retrace) and the refresh repeats, usually 60 times per second. It gives good shading and colour, and is used in TVs and monitors.

#### Numerical
```text
Screen = 8 in × 10 in, 100 pixels/in
Pixels = (8 × 100) × (10 × 100) = 800 × 1000 = 800,000
Bits per pixel = 24
Frame buffer size = 800,000 × 24 = 19,200,000 bits
Transfer rate = 10⁵ bits/s
Time = 19,200,000 / 100,000 = 192 s
```

**Answer: 192 seconds (3 minutes 12 seconds).**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. In raster display technology, what is read row by row to light pixels?
   A. The display list
   B. The vector file
   C. The deflection coil
   D. The frame buffer
   Answer: D. The display controller reads the frame buffer scan line by scan line. (Key point: Raster display)

2. How many pixels does an 8 in x 10 in screen at 100 ppi have?
   A. 800,000
   B. 80,000
   C. 8,000
   D. 1,800
   Answer: A. (8x100) x (10x100) = 800 x 1000. (Key point: Pixel count)

3. What is the frame buffer size at 24 bits per pixel?
   A. 800,000 bits
   B. 19,200,000 bits
   C. 2,400,000 bits
   D. 1,920,000 bits
   Answer: B. 800,000 x 24 = 19,200,000. (Key point: Frame buffer size)

4. How long to load at 10^5 bits/s?
   A. 19.2 s
   B. 1920 s
   C. 192 s
   D. 24 s
   Answer: C. 19,200,000 / 100,000 = 192 s. (Key point: Load time)

## Related in Computer Graphics

- [Pixel access rate of raster system](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Apixels-per-second-access-time) — Computer Graphics, chapter 1
- [Time to scan one row of pixels](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Arow-scan-time-refresh) — Computer Graphics, chapter 1
- [Frame buffer size for 1 min video](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Aframe-buffer-1min-video) — Computer Graphics, chapter 1, asked 2×
- [Random scan versus raster scan display](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Arandom-vs-raster-display) — Computer Graphics, chapter 1, asked 7×
- [Short note: Raster scan display](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Ashort-note-raster-scan-display) — Computer Graphics, chapter 1
- [Frame buffer for 640×480 B/W video](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Aframe-buffer-bw-video-5min) — Computer Graphics, chapter 1

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