3. Fundamentals of data representation

Question 1

What are the three number bases?

Answer 1

denary (base 10)
binary (base 2)
hexadecimal (base 16)

Question 2

What base do computers use to represent all data and instructions?

Answer 2

binary

Question 3

Why is hexadecimal often used in computer science? (2)

Answer 3

• large numbers can be stored using fewer digits (is a form of short-hand for coders as they do not want to type loads of 1s and 0s)
• easy to converted denary to hex to binary and vice versa

note: computers do everything in binary, only humans use hex and denary

Question 4

convert 8D (hex) to binary
(and show working)

Answer 4

10001101

8D
= 8 D
= 1000 1101
= 10001101

(you separate each character into its 4 digit binary equivalent)

Question 5

convert 10010100 (binary) to hex

Answer 5

94

Convert every 4 binary digits (from bit0) to hex digit
10010100
= 1001 0100
= 9 4
= 94

Question 6

what is the smallest/fundamental unit of information?

Answer 6

a bit (either 0 or 1)

Question 7

how many bits is a byte

Answer 7

8 bits

Question 8

write out the prefixes for bytes in ascending order

Answer 8

kilo
mega
giga
tera

all go up by 1000

Question 9

When can binary shifts be used?

Answer 9

Binary shifts can be used to perform simple multiplication/division by powers of 2, with multiplication shifting to the left and division shifting to the right.

Question 10

What is a character set?

Answer 10

All of the characters that a computer can use are called a character set

Question 11

how many bits are in extended ASCII? (1)
how many characters in the character set? (1)
what is the purpose of extended ASCII? (1)
which languages is extended ASCII suitable for? (1)

Answer 11

Extended ASCII uses eight bits (1), giving a character set of 256 characters (1). This allows for special characters such as those with accents in some languages (1) such as French and Spanish (1).

Question 12

how many bits are in unicode? (1)
how many characters in the character set? (1)
what is the purpose of unicode? (1)
which languages is it suitable for? (1)

Answer 12

Unicode is a character set which uses 16 bits (1), giving a range of over 65,000 characters (1). It is suitable for languages that contain hundreds to thousands of characters (1) such as Chinese or Arabic (1).

Question 13

Know that Unicode uses the same codes as ASCII up to 127.

Answer 13

do u know it?

Question 14

What is the purpose of Unicode and the advantages of Unicode over ASCII?

Answer 14

Students should be able to explain the need for data representation of different alphabets and of special symbols allowing a far greater range of characters.

Question 15

What is a pixel (and what is it short for)?

Answer 15

A pixel is a single point in an image and is short for picture element

Question 16

How do you calculate the size of a bitmap?

Answer 16

width (in pixels) x height (pixels)

Question 17

What is colour depth?

Answer 17

Colour depth is the number of bits used to represent each pixel.

Question 18

How do you calculate an image file size?

Answer 18

Size = (bits) = W x H x D

Size = (bytes) = (W x H x D)/8

W = image width

H = image height

D = colour depth in bits.

Question 19

sample

Answer 19

A sound measurement taken at a given point in a sound file

Question 20

amplitude

Answer 20

The size of the sound wave

Question 21

What type of data is raw, unedited sound?

Answer 21

Analogue

Question 22

How do analogue signals become digital sound?

Answer 22

• By the process of sampling.
• Where the amplitude of the sound wave is measured at regular intervals in time (for the sound)

Question 23

sampling rate

Answer 23

Sampling rate is the frequency at which a sample of a sound file is taken and is usually measured in hertz (1 hertz = 1 sample per second).

Question 24

sample resolution

Answer 24

Sample resolution is the number of bits per sample/ how much data is needed to store a sample.

Question 25

How do you calculate sound file sizes?

Answer 25

File size (bits) = rate x res x secs

rate = sampling rate

res = sample resolution

secs = number of seconds

Question 26

What is data compression?

Answer 26

Reducing the size of a certain file

Question 27

Why might data be compressed? (4)

Answer 27

• file may be too big to store
• file may be too big to transmit to someone else or too big to download
• to reduce the amount of storage space used on the hard drive
• to make downloading or transmitting a file quicker

Question 28

lossy compression

Answer 28

File compression method that permanently removes redundant data

Question 29

lossless compression

Answer 29

A file compression method that does not remove any data but compresses data by looking for a repeating pattern

Question 30

look at smth on Huffman coding idk how to make a flashcard of it

Question 31

look at something on Run-length Coding (RLE)

Question 32

RLE pros and cons

Answer 32

pro: works well in images that have blocks of the same colour, and text that has repeating symbols

con: isn’t ideal for text written in english, compression string may be larger than the actual string

Question 33

Huffman Coding pros and cons:

Answer 33

pro: compresses text very well
con: huffman trees have to be made for each string that is compressed; using a tree made from a different string might not be as efficient