4. Representing Data

Question 1

How do you convert from denary to binary?

Answer 1

Keep subtracting number by biggest base 2 that goes into it. Base 2’s that go in are 1’s in binary column.
Eg. 12 - 8 = 4
4-4 = 0
1’s in 8 and 4 column

Question 2

How do you add binary?

Answer 2

1+1 = 10 (carry the 1)
0+1 = 1
0+0 = 0

Question 3

What is it called when result of addition exceeds available space?

Answer 3

Overflow

Question 4

Why is hexadecimal used?

What does it look like

Answer 4

Represents 16 values instead of 2 of binary, so easier to remember for programmers
0-9 and then A to F

Question 5

How do you convert between hexadecimal and denary?

Answer 5

Put each digit in base 16 columns
Multiply digit by the base 16
Eg. 27 = 216 + 71

Question 6

How do you convert denary to hexadecimal?

Answer 6

Keep dividing by 16 and record remainders
Eg. 45/16 = 2 remainder 13
2/16 = 0 remainder 2
=2D (last to first)

Question 7

How do you convert from binary to hexadecimal?

Answer 7

Split split into nibbles

Value of each nibble is one digit of hexadecimal

Question 8

How do you convert from hexadecimal to binary?

Answer 8

Replace each hex digit with binary nibble

Work out denary then binary

Question 9

What is difference between ASCII and Unicode character set?

Answer 9

ASCII 7 bit (128 characters) or extended 8 bit (252 char)
Unicode 16 bit (65 000 char) or 32 (4 billion)
Unicode can include specialist symbols and multiple languages, keep 128 characters of ASCII so ASCII is subset of Unicode

Question 10

What is a character set?

Answer 10

List of codes that match characters

Question 11

What happens if you sort the list ‘Gorilla’, ‘bear’, ‘Elephant’, ‘Cat’ and ‘dog’ in a program using ASCII (or Unicode) as character set?

Answer 11

Cat
Elephant
Gorilla
bear
dog
(as A first and z last)

Question 12

What is metadata?

Answer 12

Data about the data eg. Of image

Question 13

How many colours can 1-16 bits represent

Answer 13

1 bit- two (2^1)
2 bits- four(2^2)
4 bits- sixteen (2^4)etc.
8 bits- 256
16 bits- 65 536

Question 14

What is the colour depth? Units?

Names?

Answer 14

Number of bits in a pixel (bpp)
16 bpp = high colour
24 bpp = true colour
32 bpp = deep colour

Question 15

What is the resolution? Units?

Answer 15

Number of pixels in a unit (dpi)

Question 16

What does sound metadata store?

Answer 16

Audio codec and sample rate

Question 17

How is sound interpreted by computer?

Answer 17

Sound analogue, digitally sampled by computer at the sample rate

Question 18

What happens when sample rate is low?

Answer 18

Few samples taken
Poor match between original sound and sampled sound
Small file size required

Question 19

What is the bit rate (for sound)

What does higher bit rate mean

Answer 19

Amount of space used for each sample
Higher bit rate:
More accurate sampling, better quality
More data, larger file size

Question 20

What is the bit rate for MP3 and CD?

Answer 20

128 Kbits/s

1411.2 Kbits/s

Question 21

What is instruction made up of?

Answer 21

Operator- instruction/function

Operand- data

Question 22

How does computer tell between operator and Operand?

Answer 22

They are fetched at different times in fetch execute cycle

Question 23

What is accumulator?

Answer 23

Special register in CPU, stores results of calculations

Question 24

What is the order of bits/bytes etc.

Answer 24

4 bits - 1 nibble
8 bits- 1 byte
1024 bytes - 1 kilobyte
1024 kilobytes - 1 megabyte
1024 megabytes - 1 gigabyte
1024 gigabytes - 1 terabyte