Data Representation

Question 1

What are the advantages of the design, manufacture and use of a computer system being based around the binary counting system rather than the denary (human- 0-9) counting system?

Answer 1

1. Computer circuitry is easier to design and build due to the easy mathematical rules of binary such as there only being four possible combinations when adding two binary digits.
2. A computer system is not affected by voltage fluctuations as there are only two states and so a small change in voltage would have no effect on the values stored.
3. Easier design and manufacture of storage devices which use only two states

Question 2

How are integers stored?

Answer 2

Using simple binary numbers. They are commonly stored as 8, 16, 32, 64 or 128 bit binary numbers.

Question 3

How are negative integers stored by a computer system?

Answer 3

Several methods - most common is twos complement where the left-most sided bit is used to store the negative equivalent of that column. For example, -128 would be used to make -19 (-128, 64, 32, 8, 4)

Question 4

How are real numbers stored by a computer system?

Answer 4

Using floating point notation, for example 345765000 would be stored as 3.45675x10^8 which would be stored as two separate integers - split into the mantissa and exponent with a set number of bits e.g if 32 bits are used then 24 bits may be allocated to the mantissa while the remaining 8 bits would be the exponent part of the number. This can be stored using twos complement also in order to allow negative values to be stored.

Question 5

How is text stored by a computer system?

Answer 5

Using binary number code to represent each character. Examples include American Standard Code for Information interchange which is an 8 bit code used to store 256 different text characters and Unicode which is a 16 bit code capable of storing 65 536 characters, numbers and symbols.

Question 6

Why does a computers system store and process data in binary form?

Answer 6

A computer system consists of microscopic switches called transistors which are used in computer circuitry to store and process all data. A switch only has two states (on and off) meaning that all data stored and processed by a computer system is represented using binary values that compromise the digits 0 (off) and 1 (on)

Question 7

How are vector graphics stored by a computer system?

Answer 7

Regular shapes (Polygons, Elipses, Text) and stored by saving a list of attributes for the shape
Irregular shapes are created in a vector graphics application by manipulating a series of nodes and curves which are altered by moving handles attached to each curve. The position of these nodes is then saved.

Question 8

How are sound files stored by a computer system?

Answer 8

To store sound as digital data, an analogue sound must be converted into a series of binary values by:
Taking regular ‘samples’ of single points on the wave and converting the amplitude of the wave at each point into a binary number.
A stereo sound with left and right channels will store samples for two waves

Question 9

How is the sound quality of a digitised sound determined?

Answer 9

Sample Rate - How often a sample is taken
Sample Depth - This determines the number of different values that may be used in order to store the amplitude of the wave
Higher sampling rate and depth indicate a higher quality sound - this means that the steps in the digital wave may be so small that the wave will closely resemble the original analogue wave. A lower quality sound will have larger steps between each sampled point.

Question 10

How are storage requirements for the size of a sound file calculated?

Answer 10

Number of channels x Sample Depth x Sample Rate x Sample Rate x Time (Seconds)

Question 11

How is the storage requirements for a graphic file calculated?

Answer 11

Resolution x Colour Depth

Question 12

How are video files stored by a computer system?

Answer 12

Uncompressed videos are stored as a sequence of still bit-mapped graphics.
Number of graphics stored is determined by the frame rate and video length

Question 13

How are storage requirements for a video file calculated?

Answer 13

Size of video file = Resolution x Colour Depth x Frame Rate x Time

Question 14

What does a bit-mapped graphic consist of?

Answer 14

Rows and columns of coloured pixels
Each pixel stored as a binary number
Number of possible colours being determined by the number of bits used to store each pixel
Known as its colour depth