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GCSE - Computing > 4. Data Representation > Flashcards

4. Data Representation Flashcards

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1
Q

How does binary work?

A

Each digit is a 0 or 1. The system works in base 2. That means each digit from right to left represents 1, 2, 4, 8, etc.

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2
Q

What is hex short for?

A

Hexadecimal

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3
Q

How many digits are there in hex?

A

16

0 - 9 and A - F

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4
Q

How is hex linked to binary?

A

Each hex digit is equivalent to a binary nibble of 4 digits. For example, 1110 is E.

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5
Q

How can an 8-bit binary number be written in hex?

A

Each of the two nibbles is converted to hex and then these are joined together.

For example, 1101 is D and 0100 is 4.
So, 11010100 is D4 in hex.

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6
Q

How do you convert from hex to denary?

A
  1. Convert each digit to a nibble of binary
  2. Put the two nibbles together
  3. Convert this to denary
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7
Q

How do you add two binary numbers?

A

Using column addition.
0 and a 0 make 0.
0 and 1 make 1.
1 and 1 make 0 but carry 1 to the next column.

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8
Q

What is an overflow error?

A

When the processor does not have enough bytes available to process an instruction.

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9
Q

What is a nibble?

A

4 bits

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10
Q

What is a byte?

A

8 bits

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11
Q

What is a kilobyte?

A

1024 bytes

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12
Q

What is a megabyte?

A

1024 kilobytes

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13
Q

What is a gigabyte?

A

1024 megabytes

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14
Q

What is a terrabyte?

A

1024 gigabytes

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15
Q

What is the order of ‘bytes’ in increasing size?

A 
Nibble
Byte
Kilobyte
Megabyte
Gigabyte
Terrabyte
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16
Q

What is a bitmap image?

A

An image stored as a series of values per pixel. The colour of each pixel is stored in a file.

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17
Q

What is a pixel?

A

A picture element - the smallest part of a bitmap picture.

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18
Q

What does DPI stand for?

A

Dots per inch

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19
Q

What is resolution?

A

The amount of pixels in an image. Usually measured in DPI.

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20
Q

How is binary used in a black and white bitmap picture?

A

Each pixel is represented by a 0 or 1. Only two are needed because there is only black and white.

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21
Q

What is colour depth?

A

The amount of bits used per pixel to encode the colour information.

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22
Q

How is binary used to represent pixels in a colourful image?

A

Each colour is given a binary number. If there are only 4 colours then they can be represented using 00, 01, 10 and 11.

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23
Q

What is the difference between vector and bitmap images?

A

BITMAP
• Each pixel is mapped and given a colour
• Suitable for photographs
• Quality is lost when stretched or resized
VECTOR
• Instruction for how to draw the picture are included
• Length of line, angles, curves, thickness of lines, etc.
• Best for cartoons and clip art
• Quality not lost when resized

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24
Q

What is lossless compression?

A

When a file is compressed so that picture quality remains the same and it can be decompressed into its original quality.

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25
Q

What is lossy compression?

A

When a file is compressed so that it permanently removed data. It cannot be decompressed into a file of the same quality.

26
Q

What does analogue mean?

A

A continuously varying signal - like a car speedometer

27
Q

What does digital mean?

A

A discrete value (a single number)

0s and 1s in computers

28
Q

What does ADC stand for?

A

Analogue to Digital Converter

29
Q

What is the sample rate?

A

The number of samples taken per second.

30
Q

What is sample resolution?

A

The number of bits allocated per sample.

31
Q

How is an analogue sound converted to a digital representation?

A

Using an ADC.

  1. Samples are taken multiple times per second
  2. A digital value is assigned to each sample.
  3. If a value falls between bit values, the value is rounded.
  4. The samples can be used to make a ‘graph’ showing the change in amplitude over time
32
Q

The more samples taken per second…

A

…The better the quality of the recorded sound

33
Q

What is quantisation?

A

The process of digitising an analogue sound signal.

34
Q

What is the largest number which can be shown in a byte?

A

255

35
Q

How many numbers can be shown in a byte?

A

256

36
Q

What is a character set?

A

The set of symbols that can be represented by a computer.

37
Q

What does ASCii stand for?

A

American Standard Code for Information Interchange

38
Q

What is needed for a bitmap pixel to have 4 colours?

A

2 bits per pixel

39
Q

What is Unicode?

A

Larger character set than ASCii (16 or 32 bits) and can represent many more characters from all languages.

40
Q

What is ASCii code?

A
  • 7-bit character set used by PCs.

* 128 characters represented

41
Q

What is a bit?

A

A single binary digit: 0 or 1

42
Q

What is 1024 equal to?

A

2^10

43
Q

How do you convert from denary to binary?

A
  1. Convert to binary
  2. Convert each nibble to hex
  3. Put these together
44
Q

What is F in hex equal to?

A

15

45
Q

How is a key press transmitted to a computer?

A
  • The code number of the key is transmitted to the computer

* The code number is stored as binary

46
Q

How many characters can ASCII and Unicode represent?

A

ASCII - 2^7

Unicode - 2^16 or 2^32

47
Q

Give 3 examples of character encoding systems.

A
  • ASCII
  • Unicode
  • EBCDIC
48
Q

What is EBCDIC?

A
  • Extended Binary Coded Decimal Interchange Code

* An 8-bit encoding system

49
Q

How many bits do ASCII, Unicode and EBCDIC use?

A

ASCII - 7
Unicode - 16 or 32
EBCDIC - 8

50
Q

What is metadata?

A

Data about a data file (e.g. the resolution)

51
Q

What is a vector graphic?

A

An image file that is made up of lines and shapes that have certain properties.

52
Q

What factors affect the sound quality of a digital sound?

A
  • Sample resolution

* Sample interval

53
Q

What is sound synthesis?

A

When the sound from a digital file is recreated and played through speakers.

54
Q

What is an instruction set?

A

The group of instruction available for a specific processor to use.

55
Q

What determines the number of bits used in an instruction set?

A

The number of instructions.

E.g. With 4 bits there could potentially be 16 different instructions.

56
Q

What is opcode?

A

The group of bits in a machine code instruction that represents the instruction, such as EAT, MOVE or TURN.

57
Q

What is operand?

A

The data in a machine code instruction that the operation will use, such as 5.

58
Q

What two things could the operand be?

A
  • An actual value (e.g. 5)

* An address in memory where the data can be found

59
Q

What is the difference between opcode and operand?

A

Opcode is the operation to be carried out, while operand is the data to do this with.

60
Q

How does a computer know which memory locations hold instructions and which ones hold data?

A

• Every location in memory has a specific address
• A compiled program is stored in memory with the machine code and related variables all in adjacent memory locations
• When the OS loads the program, it loads it into free space in memory and loads the start address into the processor
• The processor will continue executing instructions until it reaches a stop statement or until an error happens.
• The operand in each instruction indicates where to look for data.
• Therefore, it doesn’t matter where the program is stored in memory because the instructions in it will always be consecutive.
(See pg 59 of textbook)

GCSE - Computing (7 decks)

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