Data representation

Question 1

Character code:

Answer 1

A binary representation of a letter, character or number

Question 2

ASCII

Answer 2

A standard binary coding system for characters and number.
First was 7 bits (128 permutations), now extended to 8 bits (256 characters).
BUT 256 not enough, doesn’t cover all languages or platforms. Due to the widespread use of the web, increasing need for this. HENCE UNICODE

Question 3

Unicode:

Answer 3

A standard binary coding system that has superseded ASCII. It includes characters from over 20 countries.
16 bits, constantly updated as aims to cover every language and platform(HW and SW) and every program

Question 4

Parity bit:

Answer 4

Method of checking binary codes by counting the number of 1s and 0s. Even = even num 1’s. Odd = odd num 1’s

Question 5

Majority voting:

Answer 5

Produces same data several times and checks the same both time EG 101 - 111000111

Question 6

Check digits

Answer 6

Digit added onto end to check data is accurate, used in bar code scanners
Worked out by:
- Adding up numbers, add up that answer to get one digit BUT if digits swapped around in transmission, still get same check digit
- Modulo - 11 each num given weighting (scaling factor), times by this, add together, mod 11, remainder is check digit. ( rem = 10 ,X and rem = 11, 0)

Question 7

Why is hexadecimal preferred?

Answer 7

Useful to represent large numbers with as fewer digits as possible - 2 hex digits represent 1 byte.
USED —> identify memory addresses as less digits than binary representation

Question 8

Number Systems

Answer 8

Natural N - (0,1,2,3)
Integer Z - (-3,-2,-1,0,2)
Rational Q - (-1/2, 2.5, 3)
Irrational - (Pi, root2, root3)
Real R - EVERYTHING
Ordinal - (1st, 2nd, 3rd) used with size of lists often eg 3rd out of 30
Counting + measurement
- Natural for counting (counter used to keep track how many times looped)
- Real for measurement (microwaves control - both time and temp measured)

Question 9

Bit

Answer 9

A fundamental unit of info, either a 1 or 0

Question 10

Why comps use binary?

Answer 10

Processor only handles electricity in a simple way, flowing or not. Hence 2 states 0 (off) and 1 (on)

Question 11

How many different values can be represented with 5 bits?

Answer 11

2^5 = 32

Question 12

KMGT

Answer 12

BINARY DECIMAL
Kibi - 2^10 bytes Kila - 10^3
Mebi - 2^20 bytes Mega - 10^6
Gibi - 2^30 bytes Giga - 10^9
Tebi - 2^40 bytes Teba - 10^12

Question 13

Unsigned binary

Answer 13

Represent positive numbers

Question 14

Signed binary

Answer 14

Represent positive and negative numbers

Two’s compliment

Question 15

Max number in binary

Answer 15

2^(n)-1

Question 16

Most significant bit for 8 bits?

Answer 16

2^(n-1) = 2^7 = 128

Question 17

Twos compliment - range for 8 bits?

Answer 17

2^(n-1) -1 = 2^(7) - 1 = -128 to 127

128 is 2^(n-1)

Question 18

Convert from bits to bytes

Answer 18

/ 8

Question 19

Bit - mapped graphic

Answer 19

Image made up of individual pixels, each mapped to 1 bit of memory

Question 20

Pixels

Answer 20

Individual picture elements each mapped to 1 bit of memory

Question 21

Resolution

Answer 21

Width * Height (or pixels per inch)

Question 22

Colour depth

Answer 22

Number of bits/ bytes allocated to representing the colour of a pixel in a bit-mapped graphic

Question 23

Storage of an image?

Answer 23

Resolution * colour depth

Question 24

Metadata

Answer 24

Data about data. Bitmaps store this of themselves eg width, colour depth

Question 25

Analogue signals

Answer 25

Data that is infinitely variable and often represented in the form of a wave

Question 26

Digital signals

Answer 26

Discrete discontinuous data. either on of off

Question 27

Analogue to Digital converter

Answer 27

A series of readings are taken at fixed intervals from the wave to create discrete discontinuous values.
The more samples taken, the better accuracy to be like original copy. BUT takes up a greater file size

Question 28

Synthesized sound

Answer 28

Sound produced digitally

Question 29

File size (bits) =

Answer 29

Sample rate (hz) * length of recording (secs) * sampling resolution (bits)

Question 30

ADC Example

Answer 30

EG MIDI uses event messages to control various properties of sound (encoded in binary and provide communication between a midi device and processor
Advans over digital audio
- Small files hence less memory, loads faster (especially when file a web page)
- Completely editable (individual instruments can be selected/ modified)
- Supports wide range of instruments
- Midi files produce v high quality reproduction of instrument

Question 31

DAC example

Answer 31

• phones when playing music
• modem which is a device embedded within broadband routers that changes (modulates) a digital signal into analogue so that it can be sent down a telephone wire.
  When it is received at the other end, another modem demodulates the signal, converting it back into digital form

Question 32

Data compression

Answer 32

Process of reducing number of bits require to represent data so take up less memory

Question 33

Lossless compression

Answer 33

No data is lost
Less storage
Uses run-lenght encoding
Uses dictionary based encoding

Question 34

Run - length encoding

Answer 34

Eliminates repeating data eg blue blue blue = 3B

PICS

Question 35

Dictionary based encoding

Answer 35

Common strings of data in a text file eg tion rather than rewriting encoded
TEXT

Question 36

Lossy Compression

Answer 36

Identifies data that can be removed by Run time encoding, higher frequency data is less noticeable hence removed.
AUDIO of VIDEO