---
title: "Explain vector display"
subject: "Computer Graphics"
chapter: 1
key: "semester_5/computer_graphics:explain-vector-display"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/explain-vector-display
site: BCT Engineering
---

# Explain vector display

Computer Graphics · Chapter 1: Introduction and Application

- Asked in: 2071 Shrawan, 4 marks
- Video: [Vector Scan Display Explained in Hindi l Computer Graphics Course](https://www.youtube.com/watch?v=l5N6dv-qBzE) — 5 Minutes Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/explain-vector-display
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-1

## Question

Explain about vector display.

## Short answer

A vector display draws images as sets of line segments, steering the electron beam directly between endpoints. Only the drawn parts are refreshed from a display list of commands (MOVE, LINE). It offers high resolution but poor colour/shading and flickers with complex images.

## Answer

A **vector display** (random scan, calligraphic or stroke display) draws a picture as a series of straight line segments. The electron beam is deflected directly from one end point to the other, so only the parts of the screen that contain the picture are drawn.

```text
CPU <-> System memory
   |        (display file / list)
   v
Display processor --> Deflection --> CRT
(reads commands,         circuits
 refresh ~30-60 Hz)
```

**Working**
1. The application program and graphics package store the picture as line-drawing commands (e.g. MOVE, LINE) in a **display list** (refresh display file).
2. The display processor (display controller) reads the commands in turn and moves the beam along each line.
3. Because the phosphor glows only for a short time, the whole list is redrawn 30 to 60 times per second to refresh.

**Features**
- Small memory (only commands stored).
- Very high resolution, smooth lines without staircase effect.
- Flicker appears if the display list is long.
- Poor for filled areas, shading and many colours.
- Used in early CAD, plotters and radar-type displays; now largely replaced by raster displays.

## Check yourself

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

1. How does a vector display draw?
   A. It sweeps all rows
   B. It lights pixels from a frame buffer
   C. Beam is deflected directly from one endpoint to another along straight lines
   D. It uses a backlight
   Answer: C. Only the picture parts are drawn. (Key point: Principle)

2. Where is the picture stored?
   A. In a frame buffer of pixels
   B. In the video RAM only
   C. In a colour table
   D. As line-drawing commands in a display list
   Answer: D. The display file holds MOVE/LINE commands. (Key point: Storage)

3. Why is the display list redrawn 30-60 times per second?
   A. Phosphor glows only briefly
   B. To save memory
   C. To raise resolution
   D. To reduce cost
   Answer: A. Without redrawing the picture fades. (Key point: Refresh)

4. Which is a feature of vector display?
   A. Good shading
   B. Smooth lines but poor for filled areas and many colours
   C. Jagged lines
   D. Large memory
   Answer: B. Vector is high resolution but poor for fills. (Key point: Features)

## Related in Computer Graphics

- [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×