1.2 Memory and storage

Question 1

What are the 3 number systems?

Answer 1

• Denary (base 10)
• Binary (base 2)
• Hexadecimal (base 16)

Question 2

Denary

Answer 2

• 10 Digits: 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9
• Place values are powers of 10 (100s, 10s, 1s)

Question 3

Binary

Answer 3

• 2 Digits: 0 and 1
• Place values are powers of 2 (8s, 4s, 2s, 1s)

Question 4

Hexadecimal

Answer 4

• 16 Digits - 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E and F
• Place values powers of 16 (256s, 16s, 1s)

Question 5

Converting binary to denary

Answer 5

• Put the number in a binary place value table
• Add up the place values in columns where there’s a 1

Question 6

Converting denary to binary

Answer 6

• Draw a binary place value table
• Keep subtracting the biggest place values you can until you’re left with 0
• If you subtracted a place value, put a 1 in that column, otherwise put a 0

Question 7

Converting Hex to Denary

Answer 7

• Put the number in a hex place value table
• Convert each value to hex
• Add up the results

Question 8

Converting Denary to Hex

Answer 8

• Dividing by 16 to get a quotient and a remainder
• Convert each to hex
• The quotient is the 1st digit and the remainder is the 2nd

Question 9

Converting Binary to Hex

Answer 9

• Put the numbers in a table that repeats 8, 4, 2, 1
• If the binary isn’t 8 bits, add 0s to the front so that it can split into nibbles
• For each nibble, add up the place values in columns where there’s a 1, and convert into hex

Question 10

Converting Hex to Binary

Answer 10

• Convert each hex digits into a 4-bit binary number
• Put the nibbles together

Question 11

Binary addition

Answer 11

• Use column addition
• Follow the 4 rules:
  1) 0 + 0 = 0
  2) 1 + 0 = 1
  3) 1 + 1 = 10 (carry a 1)
  4) 1 + 1 + 1 = 11 (carry a 1)

Question 12

Binary shifts

Answer 12

• Move every bit left or right a certain number of places
• Gaps at the beginning or end of the number are filled in with 0s
• Left shifts -> Multiplying -> For every place, number is doubled
• Right shifts -> Dividing -> For every place, number is halved

Question 13

Overflow error

Answer 13

• When binary arithmetic gives a result that requires more bits than the CPU is expecting
• Can lead to a loss of data or precision
• In binary addition, two 8-bit numbers might add to give a 9-bit number. If the CPU expects an 8-bit answer then bits will be lost
• Left shifts can cause the most significant bits to be lost
• Right shifts can cause the least significant bits to be lost

Question 14

Eight units of data size

Answer 14

• Bits (b) -> a single binary digit (1 or 0)
• Nibble -> 4 bits
• Byte (B) -> 8 bits
• Kilobytes (kB) -> 1000 bytes
• Megabyte (MB) -> 1000 Kilobytes
• Gigabyte (GB) -> 1000 Megabytes
• Terabyte (TB) -> 1000 Gigabytes
• Petabyte (PB) -> 1000 Terabytes

Question 15

How does computer store and process data?

Answer 15

• Binary
• Use 0s and 1s to represent flow of electricity -> 1 shows electricity is flowing, 0 shows that it isn’t flowing
• Each 1 or 0 in binary data is a bit. The size of the file is the numbers of 0s and 1s that make up its data

Question 16

Data compression

Answer 16

Making file sizes smaller, while trying to stay as true to the original as possible

Question 17

Benefits of data compression

Answer 17

• Compressed files use less storage space
• Streaming/downloading takes less bandwidth
• Some services like email have file size limits -> compression can get a file below the limit

Question 18

Two types of compression

Answer 18

• Lossy compression -> permanently removes data from the file
• Lossless compression -> Temporarily removes data to store the file, and restores it to its original state when opened

Question 19

Advantages of lossy compression

Answer 19

• Big reduction in file size -> easier to store, faster to download
• Commonly used -> lots of software can read lossy files

Question 20

Disadvantages of lossy compression

Answer 20

• Loses data -> can’t be turned back into the original
• Can’t be used on text/software
• Reduction in quality

Question 21

Disadvantages of lossless compression

Answer 21

• Comparatively small reduction in file size -> lossless files take up more storage space than lossy files

Question 22

Characters

Answer 22

Uppercase and lowercase letters, the digits 0-9, and symbols like ?, + and £. Used to make words and strings

Question 23

Character sets

Answer 23

Collections of characters that a computer recognises from their binary representation, used to convert characters to binary code and vice versa

Question 24

ASCII

Answer 24

• Each character is given a 7-bit binary code -> can represent 128 different characters
• Extra 0 is added to the start of each binary code so each character uses 1 byte

Question 25

Unicode

Answer 25

• Covers all major languages, including ones that use different alphabets
• Uses multiple bytes for each character
• First 128 characters in Unicode are the same as ASCII

Question 26

Text file sizes

Answer 26

File size (in bits) = number of bits per character x number of characters

Question 27

Bitmap

Answer 27

A type of image made up of lots of tiny dots, called pixels. Colour of each pixel is stored using a binary code

Question 28

Image resolution

Answer 28

Number of pixels in a bitmap image -> width x height

Question 29

Colour depth

Answer 29

The number of bits used to represent each pixel -> total number of colours = 2 to the power of n (where n = colour depth)

Question 30

Image file sizes

Answer 30

• File size (in bits) = image resolution x colour depth = width x height x colour depth
• Increasing the image resolution or colour depth will usually give a higher quality image, but a larger file size

Question 31

Metadata

Answer 31

Data stored in a file which contains information about the file. Helps the computer to recreate the image on the screen from the binary data

Question 32

Sampling

Answer 32

Converting an analogue sound wave into digital data that can be read and stored by a computer

Question 33

Sample rate

Answer 33

The number of samples taken per second. It is usually measured in hertz (Hz).

Question 34

Bit depth

Answer 34

The number of bits available for each sample

Question 35

Sound sampling process

Answer 35

• The amplitude of the sound wave is measured at fixed intervals -> sample rate
• Recreated digitally based on the measurements taken -> bit depth
• Will have lost some accuracy

Question 36

Sound file sizes

Answer 36

File size (in bits) = Sample rate (Hz) x bit depth x length (seconds)