Chapter 4 - Representing Data

Question 1

In binary what does 
1 + 0 =
1 + 1 =
0 + 0 =
1 + 1 + 1 =

Answer 1

1 + 0 = write 0 carry 1 over
1 + 1 = write 0 carry 1 over
0 + 0 = write 0
1 + 1 + 1 = write 1 carry 1 over

Question 2

What is an overflow error?

Answer 2

When the result of an addition is too big to fit in the available space
Eg. When a computer uses storage values that are 8 bit long, by adding two 8 bits long numbers, the result may be bigger than 256 - you need a 9th binary digit, the 9th digit will be lost

Question 3

Count to 15 in hexadecimal

Answer 3

0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F

Question 4

Why use hexadecimal numbers?

Answer 4

Large binary numbers are hard to remember and programmers want something that is easily converted from binary an easy to remember and recognise

Question 5

How are images stored?

Answer 5

Images are stored as a series of binary values, each binary value is one pixel

Question 6

What is metadata and why is there a need for it?

Answer 6

Metadata is data about data
It includes height and width, resolution, but depth etc
There is a new for metadata because it enables the computer to work out how to turn these binary values into an image

Question 7

What is height and width measured in?

Answer 7

Pixels

Question 8

What is couloir depth?

Answer 8

The number of bits used per pixel, or how many colours each pixel can represent
1 bit = 2 colours black or white
2 bits = 2*2 colours or 4 colours
Etc.
The more bits per pixel the greater the colour depth

Question 9

What is resolution?

Answer 9

Number of pixels per unit eg number of pixels per inch or dpi (dots per inch)

Question 10

The higher the colour depth and the higher resolution, what happens to the size of an image file?

Answer 10

It increases

Question 11

When does an image become pixelated?

Answer 11

When a bitmapped image is enlarged

Question 12

What are the units of storage?

Answer 12

Bit 
Nibble
Byte
Kilobyte
Megabyte
Gigabyte
Terabyte

Question 13

How are characters steed?

Answer 13

All characters and symbols are represented by a code
The codes used are stored in binary
The computer looks up the symbol matching the code from a list of codes and their associated character

Question 14

What is a character set?

Answer 14

The list of codes and matching characters is called a character set

Question 15

What determines how many symbols are in a character set?

Answer 15

The number of bits used to store each symbol

Question 16

Examples of character sets?

Answer 16

Unicode

ASCII

Question 17

How many bits does ASCII use?

Answer 17

8 bits per character = 256 possibilities

Question 18

How many bits does uni code use?

Answer 18

16 bit providing 65 000 possibilities

Or 32 bits = 4 billion possibilities

Question 19

Why is unicode better than ascii?

Answer 19

Because it provides a wider range of characters and symbols facilitating communication

Question 20

What is sound and how is in stored in digital form?

Answer 20

Sound is analogue (continuously varying) so to transfer sound to a computer it must be digitally sampled.

Question 21

What is sample rate?

Answer 21

The number of samples in a second

Question 22

What is sample interval?

Answer 22

The time between samples been taken

Question 23

The higher the sample interval…

Answer 23

The lower the sample rate

Question 24

When a sound is sampled at a low rate:

Answer 24

Very few samples are taken
There is poor match between the original sound and the samples sound
A small file size is required

Question 25

When sound is samples at a high rate:

Answer 25

Many more samples are taken
There is a good match between the original sound and the sampled sound
A large file size is required

Question 26

What is bit rate?

Answer 26

The amount of storage space used for exam sample

Question 27

A high bite rate means:

Answer 27

More accurate sampling at each point which gives better quality
More data needs to be stored so larger file size

Question 28

What are the two parts of an instruction?

Answer 28

Operator: the instruction part eg. An operation
Operand: the data part, it is what the operator uses eg. A memory location

Question 29

How does a computer tell the difference between data and instructions?

Answer 29

It doesn’t, it simply deals with what it finds according to what it expects to find

Question 30

What is the accumulator?

Answer 30

A special register in the CPU used to store the results of any calculation