1.4.1 Data Types

Question 1

What is a character set?

Answer 1

• A defined list of characters recognised by the computer hardware and software, with each character being represented by a single number
• Character sets are agreed standards for referring to all characters a computer uses
• Includes upper/lower case symbols and punctuation

Question 2

How many unique binary numbers does 7 bits give?

Answer 2

128

Question 3

What is ASCII?

Answer 3

• American Standard Code Information Interchange became the accepted standard.
• It was then extended from 7 bit to 8 bit - Extended ASCII

Question 4

How many unique binary numbers with 8 bits?

Answer 4

256

Question 5

An international, multilingual language character set needs to include:

Answer 5

• Characters from every written language
• Historical scripts
• Emojis

Question 6

What is UNICODE?

Answer 6

• Was originally 16 bit but is now 24 bit character set providing over 16 million characters
• Writing 24 bits is slow, so hexadecimal is used instead

Question 7

Why don’t we use UNICODE all the time?

Answer 7

• The ASCII Character set is an 8 bit character set, meaning each unique character in a file is represented by 8 1s or 0s
• The Unicode Character set is 8, 16 or 32 bit character set depending on version, therefore each character is either 8, 16 or 32 1s or 0s
• Text file stored using UNICODE can take up more space than ASCII

Question 8

Exam Question: What is meant by the character set of a computer?

Answer 8

• Normally equates to the symbols on a keyboard/ digits/ letters
• That can be represented/ interpreted/ understood by a computer
• May include control characters

Question 9

Exam Question: Explain how codes are used to represent a character set?

Answer 9

• Each symbol has a (binary) code / number
• Which is unique
• Number of bits used for 1 character = 1 byte
• Example code: ASCII / UNICODE
• Uses 8 bits/ 16 bits per character
• Use of more bits for extended character set

Question 10

Exam Question: The character A in the ASCII character set is represented by the denary value 65. Write the binary representation for the ASCII character “H”. Show your working. (2)

Answer 10

• If A is 65, H is 72
• 72 in binary is 01001000

Question 11

Describe what is meant by the term ASCII ?(2)

Answer 11

• American Standard Code for Information Interchange
• A character set
• Maps values to characters
• Uses 7 bits/8bits per character

Question 12

Exam Question: Explain what is meant by the term UNICODE? (3)

Answer 12

• Unicode is a character set
• Mapping different binary values to characters
• Each character is represented by 1-4 bytes
• It supports a very large number of characters
• It is backward compatible with ASCII

Question 13

What are the 5 primitive data types?

Answer 13

• Integer
• Real/floating point
• Character
• String
• Boolean

Question 14

What is an integer and give an example?

Answer 14

• A whole number
• 23

Question 15

What is a real/floating point and give an example?

Answer 15

• A number with an integer and a fractional part
• 12.65

Question 16

What is a character and give an example?

Answer 16

• A single alpha-numeric character
• D

Question 17

What is a string and give an example?

Answer 17

• A sequence of alpha numeric characters
• Hello

Question 18

What is Boolean and give an example?

Answer 18

• Either TRUE or FALSE
• FALSE

Question 19

How do you represent positive 11 in a 4 bit binary system?

Answer 19

• 1011

Question 20

How do you represent 121 into binary?

Answer 20

• 01111001

Question 21

What are the 2 ways to represent negative numbers in binary

Answer 21

• Sign and Magnitude
• Two’s complement

Question 22

How do you use sign and magnitude to represent a negative number in binary?

Answer 22

• The most sig fig is used to represent the sign
• 1 means the number is negative and 0 means the number is positive

Question 23

How would you convert -4 into binary using sign and magnitude?

Answer 23

• Write out positive 4 in binary
• Then change the MSB to 1
• 10000010

Question 24

Why is Sign and magnitude not used often?

Answer 24

• Largest number that can be represented using 8 bits is 127 due to using MSB as a sign bit much less than 255
• Also harder to do calculations as some bits mean different things; some numbers and some signs

Question 25

How do you represent a negative number using Two's complement?

Answer 25

* To write it out as a positive number * Then starting from the right hand side, flip each bit and then add 1

Question 26

Convert -86 into binary using Two's complement

Answer 26

* Work out + 86: 01010110 * Then flip: 10101001 * And add 1: 10101010

Question 27

What is 1. 0+0 2. 0+1 3. 1+1 4. 1+1+1 ?

Answer 27

1. 0 2. 1 3. 10 4. 11

Question 28

How do you do Binary Addition?

Answer 28

* Arrange them above each other * Start at Least Significant Bit and add the 1s and 0s

Question 29

How do you do Binary subtraction?

Answer 29

* Same as binary addition but convert the number to be subtracted into a negative number using 2s complement

Question 30

Binary addition: What is 42+18

Answer 30

00111100

Question 31

Binary subtraction: What is 68 - 33

Answer 31

* 00100011

Question 32

What are the different symbols used in hexadecimal and what do they mean?

Answer 32

* 0 - 9 = 0 - 9 * A=10, B = 11, C=12, D=13, E = 14, F = 15

Question 33

How do you convert the denary number 31 into hexadecimal?

Answer 33

* 1F

Question 34

What are the steps of writing a number into floating point notation?

Answer 34

* Convert the exponent into denary. * If the exponent is positive, move the decimal point to the right, if negative move decimal point to the left * Put column headings under and add the value

Question 35

How do you normalise a number - if positive?

Answer 35

1. Convert exponent to denary 2. Move decimal point so it is before the first 1 3. Subtract the number of moves from the exponent

Question 36

How do you add floating point numbers?

Answer 36

1. The exponents of the 2 numbers must be the same 2. Change the exponent of the 2nd number to the first exponent and adjust mantissa 3. Add mantissas using usual method

Question 37

Add Mantissa: 01110, Exponent 010 and Mantissa 01000, Exponent 001 together?

Answer 37

* 10010 010

Question 38

How do you subtract floating numbers?

Answer 38

1. Just like addition, exponents must be the same and adjust mantissa 2. Now convert the mantissa of the second number to a negative one using 2s complement 3. Add the mantissas

Question 39

Subtract Mantissa: 01110, Exponent: 010 from Mantissa: 01000, Exponent 001

Answer 39

* 01010 010

Question 40

What is Bitwise Manipulation and masks?

Answer 40

* Bitwise Manipulation means applying logical operators (AND, OR, NOT, XOR) to binary * Mask is simply data being used in the operation

Question 41

How do you carry out Bitwise Manipulation?

Answer 41

* Apply operations to corresponding bits * A = 10111001 * B = 00111010 * AND = 00111000