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Computer science > 4.5 Data representation > Flashcards

4.5 Data representation Flashcards

points 4.5.1 - 4.5.5 by 13/12/2023

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1
Q

What is the symbol for a natural number ?

A

N

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2
Q

What is a natural number ?

A

Set of infinite positive whole numbers.

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3
Q

What is the symbol for an integer ?

A

Z

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4
Q

What is an integer ?

A

Infinite set of both positive and negative whole numbers.

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5
Q

What is the symbol for a real number ?

A

R

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6
Q

What is a real number ?

A

Any positive or negative number including those with a decimal , fraction or infinite decimal expansion. (Rational + Irrational)

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7
Q

What is the symbol for a ration number ?

A

Q

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8
Q

What is a rational number ?

A

A number that can be expressed as the ratio of two integers (neither zero)

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9
Q

What is error trapping ?

A

When the denominator of a fractional part is zero producing an unknowable.

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10
Q

How is an irrational number defined ?

A

R/Q or R-Q

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11
Q

What is an irrational number ?

A

An irrational number has an infinite number of decimal places without ever slipping into a pattern so cannot be represented by a fraction.

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12
Q

What is an ordinal number ?

A

A natural number describing the numerical position of a value.

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13
Q

What is an array pointer ?

A

Ordinal number that points to a specific position in the sequence - start at zero unless stated otherwise.

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14
Q

What is a number base ?

A

A number base is the number of digits or combination of digits that a system uses to represent numbers.

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15
Q

What base is binary?

A

2

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16
Q

What base in denary?

A

10

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17
Q

What base is hex?

A

16

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18
Q

Why is hex used as shorthand for binary ?

A

Easier to interpret, uses less digits and is therefore less likely to be recorded incorrectly. eg. MAC addresses and RGB values

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19
Q

Values and notation for prefixes : kilo, mega, giga, tera

A

10^3 (kB) , 10^6 (MB) , 10^9 (GB) , 10^12 (TB)

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20
Q

Values and notation for prefixes : kibi, mibi, gibi, tebi

A

2^10 (KiB) , 2^20 (MiB) , 2^30 (GiB) , 2^40 (TiB)

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21
Q

If number of bits is ‘n’ how many binary sequences can a bit represent ?

A

2^n

eg .1bit –> 2
3bits –> 8
8bits –> 256

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22
Q

What is word size ?

A

The amount of data that can be handled at one time by the processor

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23
Q

Convert 1011.0011 from Fixed point binary to denary

A

11 3/16

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24
Q

what do the 4 bits after the pint in fixed point binary represent ? (.0000)

A

2^-1 = 0.5
2^-2 = 0.25
2^-3 = 0.125
2^-4 - 0.0625

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25
Q

Using twos compliment, If the left most bit of a binary number is a ‘1’ is it positive or negative ?

A

Negative

26
Q

What is the range of values on byte in twos compliment can represent ?

A

-128 –> 127

27
Q

Convert -45 (denary) to binary using twos complement.

A

11010011

28
Q

How do you subtract in binary ?

A

Add a positive and negative number using two’s compliment.

29
Q

Do 15-67 (Give answer and do working in binary)

A

-67+15

10111101 + 00001111

= 11001100 (-52)

30
Q

01=
00=
1*1=

A

01=0
00=0
1*1=1

31
Q

multiply 11 by 1101

A

x 11
1101
1101 +
11010 = 110111

32
Q

multiply 1010 by 1101010

A

10000100100

33
Q

What does ASCII stand for ?

A

American standard code for information interchange

34
Q

How many bits does ASCII use to represent each character ?

A

8 bits (256 chars)

35
Q

What is a character set ?

A

A standardised collection of characters with corresponding character codes

36
Q

What is a control character ?

A

Codes designed to trigger certain actions on peripheral devices eg. Tab. In ascii characters 0-31.

37
Q

What is unicode ?

A

Universal international character set allowing for special characters and symbols.

38
Q

Name and Describe the three encoding standards

A

UTF8 - 8 bit so compatible with ASCII and allows for variable width encoding so can expand to deal with larger sets of characters.

UTF16 - 16 Bits and allows variable width encoding to expand to 32.

UTF32 - Each character uses exactly 32 bits (fixed width)

39
Q

What is the formula for calculating size of text files ?

A

No. chars * Bits per char

40
Q

What isa character code ?

A

When a numeric digit is processed as a character, the computer uses the binary pattern of the character code rather than the pure binary representation of the numeric value.

eg. 35 = 00100011
or
3 char code = 00110011
5 char code = 00110101

41
Q

What is ‘noise’ in cables?

A

Electromagnetic interference

42
Q

Does a longer cable have more or less noise ?

A

More

43
Q

What is a transmission error

A

noise can cause corruption of a bit, a logic 1 is read as 0 and 0 as 1

44
Q

What is a parity bit ?

A

An extra bit added to the end or start of a byte to make the total number of 1’s odd (odd parity) or even (even parity)

45
Q

What is the purpose of a parity bit ?

A

To allow the receiving end to detect errors in transmission

45
Q

What decides the position and type of the parity bit ?

A

The protocol

45
Q

Which of these doesn’t have an error ?

a) 0111101 EVEN PARITY BIT ADDED : 10111101
Received :10111100
b)1010110 EVEN PARITY BIT ADDED : 01010110
Received : 01010110

A

b as there is still an even number of 1’s

46
Q

What does the computer do if fit knows an error has occurred ?

A

Requests for it to be resent

46
Q

What is majority voting ?

A

Every bit is repeated an odd number of times before transmission.
eg 110 = 111 111 000

46
Q

Cons of parity bits

A

They can detect whether an error is present but not its position. If there are two errors there will still be an odd/ even no. of ones depending on the parity type and it will not be detected.

47
Q

How does majority voting work ?

A

If each bit is repeated an odd amount of times the correct bit can be assumed as the one that appears most of the time.

eg. 111 011 000

we can assume the correct data is 110 with one erroneous bit.

48
Q

Cons of Majority voting

A

If two bits are erroneous it isn’t always correct. The chance of this can be reduced by multiplying by a larger number but then more redundant information is transmitted (than necessary)

49
Q

What is a checksum algorithm ?

A

Algorithm attached to a piece of data that returns a value and is transmitted with the data.

50
Q

How does checksum work ?

A

The receiver calculates their checksum value using the same algorithm and the data they received to see whether the checksums are the same. If not there is an error.

51
Q

What is a a longitudinal parity check ?
(in regards to checksum error detection)

A

Way of producing a check sum by dividing data into a set number of bits. It calculates the XOR values for each of columns in these chunks and adds them together to create a checksum.

52
Q

How does the sum compliment work ?
(in regards to checksum error detection)

A

Divides data into sets of bits and adds them . The check sum is equal to the twos compliment answer of the sum Ignoring the overflow bits.

53
Q

What is a check digit ?

A

Extra digit added to the beginning of a long number to identify its product eg. Bank numbers or social security numbers or ISBNs.

54
Q

What is a check digits purpose ?

A

To recognise and prevent human errors when typing in a long number.

55
Q

How are check digits produced ?

A

Using modulo arithmetic - Multiply the digit in the number by its position and then add all of the products. Then perform mod x.

56
Q
A

Computer science (7 decks)

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