1.4.1 Data Types - Done

Question 1

Name each primitive data type

Answer 1

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

Question 2

What is the purpose of data types?

Answer 2

They are needed so the computer knows how to store, process and interpret data correctly so that only valid operations are performed on data.

Question 3

What is an integer?

Answer 3

A whole number

Question 4

What is a real/floating point data type?

Answer 4

A decimal number

Question 5

What is a character?

Answer 5

A single letter, digit or symbol

Question 6

What is a string?

Answer 6

A sequence of characters

Question 7

What is a boolean data type?

Answer 7

A data type with only 2 possible values – true or false

Question 8

What types of data can be represented in binary?

Answer 8

Numeric, text, image and sound

Question 9

How is binary used to represent text?

Answer 9

Through their use of the character sets ASCII and Unicode. Each character is given a unique binary code. Increasing the number of bits for each character increases the number of possible characters that can be stored

Question 10

How is binary used to represent numbers?

Answer 10

Positive denary numbers can be represented through binary. Negative binary numbers can be stored using Sign and Magnitude and Two’s Compliment. Floating point binary can be used to store decimal numbers.

Question 11

How is binary used to represent images?

Answer 11

Images are split into pixels. Each pixel is given a binary value which represents colour.

Question 12

How is binary used to represent sound?

Answer 12

Analogue sound is sampled. A sample is a reading that is taken at a certain point and stored as a binary number.

Question 13

Why do computers use binary?

Answer 13

Computers are made up of switches which have 2 states: on and off. This can be easily represented using binary as it also has 2 states that can represent on and off: 1 and 0.

Question 14

Describe Sign and Magnitude

Answer 14

The number is written the same as in regular binary, however the left-most bit has become a sign bit (no longer representing a weighted value, but instead a sign) with 1 representing a negative number and 0 for if the number is positive.

Question 15

Describe Two’s complement

Answer 15

Negative numbers are represented starting from 11111111 as the denary value -1.

Starting from the right-most digit, you write the binary number exactly how it would appear in regular binary, up to and including the first 1. From that point onwards, swap every 0 for a 1 and vice versa.

Question 16

State the advantages of storing values using Two’s complement rather than Sign and Magnitude

Answer 16

• Calculations are easier to perform
• Two’s complement allows for a larger range of numbers to be stored
• It has only one representative station for 0
• No additional hardware is required

Question 17

Describe how to do binary subtraction using the borrowing method

Answer 17

1 - 1 = 0
1 - 0 = 1
0 - 0 = 0
0 - 1 = 1, make the next digit of 1 a 0 and the digit to the right of it a 2

Question 18

Describe how to do binary subtraction using Two’s complement

Answer 18

Add the negative version of one number to the positive of the other number to get the two’s complement form of the result.
[a - b = a + (-b)]

Question 19

What are the benefits of using hexadecimal over binary?

Answer 19

-Hexadecimal values are shorter than binary so 4 bits can be represented using one character
-This means they are faster, and more reliable to write down and read

Question 20

How are decimal numbers represented in floating point binary?

Answer 20

The mantissa of a floating point number holds the actual digits of the value and represents the precision of the number. It’s usually 5 bits long.

The exponent controls the size of the number as it governs where the decimal point is positioned. It’s usually 3 bits long. The exponent is written in Sign and magnitude.

The decimal point starts between the first and second digits. If the exponent is positive the decimal moves right, if it’s negative it moves left.
Each digit after the decimal represents 1/2^n (with n increasing the lower the digit is).

Question 21

What is the benefit of using a normalised form when representing data as a floating point number?

Answer 21

• It allows for greater accuracy from the given number of bits.
• The representation of each binary value is unique.

Question 22

Describe how a normalised number should appear

Answer 22

A floating point where the mantissa starts with 01 if positive or 10 if negative.
The normal exponent should be the difference between where the decimal point would be based on the original exponent and where it is after normalisation (negative if the normalised is further right, positive if it’s further left)

Question 23

How do you perform a logical shift?

Answer 23

By moving all the bits in a binary number left/right a set number of places.
In a right shift, the right most bits should be discarded. In a left shift, the empty righthand bits should be filled with zeros.

Question 24

What do right and left shifts do to the numbers?

Answer 24

A right shift divides the number by 2, a left shift multiplies the number by 2.

Question 25

What is a mask?

Answer 25

A binary pattern used with bitwise operations to manipulate specific bits within a binary value.

Question 26

Describe the use of the AND mask

Answer 26

Both bits are needed to be 1 for the result to be 1. An AND mask is used to clear (Set to 0) specific bits, as any bit ANDed with 0 becomes 0 and with 1 stays the same.

Question 27

Describe the use of the OR mask

Answer 27

1 or both bits need to be 1 for the result to be 1. An OR mask is used to set (turn on) specific bits as any bit ORed with 1 becomes 1 and with 0 stays the same.

Question 28

Describe the use of the XOR mask

Answer 28

1 bit (but NOT both) needs to be 1 for the result to be 1. A XOR mask is used to toggle (invert) specific bits as any bit XORed with 1 flips and, when XORed with 0 stays the same.

Question 29

Define a character set

Answer 29

A list of characters (that can be understood by the computer) where each character is given a unique binary value that is stored instead of the character

Question 30

Describe ASCII

Answer 30

The American Standard Code for Information Interchange uses 7 bit binary (128 characters) to represent characters. Extended ASCII uses 8 bits (256 characters).

Question 31

What's the advantage of ASCII?

Answer 31

It's simple and compact and takes up less memory.

Question 32

What's the disadvantage of ASCII?

Answer 32

The limited number of bits means it can only store English characters, and doesn't have the space to store a wider variety of characters.

Question 33

Describe Unicode

Answer 33

Unicode is a character set that uses up to 32 bits to represent characters using binary numbers.

Question 34

What is the advantage of Unicode?

Answer 34

It includes over 140,000 characters, allowing consistent representation of text across different devices and platforms and for characters from a variety of languages and writing systems to be represented digitally.

Question 35

What is the disadvantage of Unicode?

Answer 35

The greater number of bits it utilises means it take ups more memory than ASCII.