Computer Systems (Data Representation)

Question 1

How are positive numbers represented in a Computer

Answer 1

They are represented in binary

Question 2

128 64 32 16 8 4 2 1

1 0 0 0 0 1 1 1

What decimal number is represented in binary by 10000111?

Answer 2

135

Question 3

How are real numbers represented?

Answer 3

Real numbers must be able to store decimal numbers the floating point system is used.

Question 4

Explain how the floating point system works?

Answer 4

The Mantissa dictates the precision of numbers and the Exponent dictates the range

Question 5

What is the mantissa in a floating point system?

Answer 5

The number of bits allocated to the Mantissa dictates the precision of a real number. More bits to the Mantissa leads to greater precision. Less bit leads to less precision.

Question 6

What is the exponent in a floating point system?

Answer 6

The number of bits allocated to the Exponent dictates the range of a real number. More bits to the Exponent leads to greater range. Less bit leads to less range.

Question 7

What is Extended ASCII?

Answer 7

Extended ASCII is one way to represent a character set. Extended ASCII code uses 8 bits to represent a character meaning that you can represent up to 256 different characters.

Question 8

What are printable characters (ASCII)?

Answer 8

Printable characters are those that you will be able to see on screen. They have an 8 bit ASCII code. Examples are: A, s, !, @

Question 9

What are control characters (ASCII)?

Answer 9

Control Characters are those that do not appear on screen but that carry out a task. They have an 8 bit ASCII code. Examples are:
Shift, Delete, Backspace, F2, Ctrl

Question 10

What are bit-mapped graphics?

Answer 10

Bit Mapped graphics are made up of a 2D array of pixels. Every single pixel is saved. JPEG, PNG and GIF are bit mapped graphic formats.

Question 11

What talking about colour depth for graphics, what is bit depth?

Answer 11

Every pixel is stored as a binary code. Bit depth is the number of bits used to store each pixel. A bit depth of 8 bits allows the pixel to be one of 256 colours, a bit depth of 16 bits allows for 65,536 colours and a bit depth of 24 bits allows for 16, 777, 216 colours. The higher the bit depth the larger the file size but the more colour available.

Question 12

What is the resolution of an image?

Answer 12

Resolution is the total number of pixels in an image.

E.g. A resolution of 800 x 600 would create 480,000 pixels

Question 13

What are vector graphics?

Answer 13

Vector graphics are NOTstored as individual pixels. Instead a description of attributes is used to create an object/shape. E.g. for a circle the attributes might be: cx (centre x), cy (centre y), rx (radius x), ry (radius y), fill, line. The computer uses the attributes to create shapes.
Vector graphics usually have smaller file sizes than bit
mapped graphics as you don’t need to store every pixel.

Question 14

Name and describe four differences between bit-mapped and vector graphics

Answer 14

Scaling – Bit Mapped could be pixelated, vector would retain quality

Editing –Every pixel can be edited for fine detail in bit
mapped graphics, in vector, fine detail is harder to edit as you can only change individual attributes

Layering – Bit maps don’t let you layer shapes, whereas vectors do

File Size –bit mapped usually larger as every pixel is stored, whereas only attributes are stored in vector

Question 15

With regard to vector graphics, what is a rectangle and how would it be stored?

Answer 15

Rectangle is a type of polygon but given the frequency of its use, most vector graphic file formats support a specific rectangle object. Squares could be created using either the rectangle or polygon objects.
Attributes: x, y, fill, line, height, length. x and y define the top left corner position

Question 16

With regard to vector graphics, what is an ellipse and how would it be stored?

Answer 16

Ellipse objects are like circles, but you can alter the radius of the X co-ordinate so that it is a different value to that of the Y co-ordinate. This allows for the creation of oval shapes rather than circles.
Attributes: cx and cy define the centre, rx and ry the radius. Fill and line.

Question 17

With regard to vector graphics, what is a line and how would it be stored?

Answer 17

The line object allows for the creation of lines. More complex lines with different points can be created using an object called a polyline.
Attributes: x1 and y1 define the start of the line, x2 and y2 define the end of the line. Line is used for the colour of the line. Fill IS NOT NEEDED for lines.

Question 18

With regard to vector graphics, what is a polygon and how would it be stored?

Answer 18

The polygon object can be any shape that has at least three sides and allows for a wide variety of common shapes to be stored in vector form.
At every angle, x and y coordinates are needed, soa shape with five angles would have:
Fill, line, x1, y1, x2, y2, x3, y3, x4, y4, x5, y5