OCR A Level CS 1.4.1 Data Types

What are the five primitive data types?

Integer, Real/Floating Point, Character, String, Boolean.

What is a character?

A single symbol used by a computer (e.g., A, 7, %).

How do computers store integers?

Using binary (base 2), where each bit represents a power of 2.

What is a byte?

8 bits.

What is a nibble?

4 bits (half a byte).

What are the two main methods to represent negative numbers in binary?

Sign magnitude and Two’s complement.

How does sign magnitude work?

The leftmost bit represents the sign (0 = positive, 1 = negative).

What is a problem with sign magnitude?

It has two representations for zero (00000000 and 10000000).

How does two’s complement work?

The most significant bit (MSB) represents a negative value.

How do you convert a number to two’s complement?

Flip all bits and add 1.

What are the four rules of binary addition?

• 0 + 0 = 0

• 0 + 1 = 1

• 1 + 1 = 10 (carry 1)

• 1 + 1 + 1 = 11 (carry 1)

How is binary subtraction done?

By using two’s complement and then adding.

What is hexadecimal (hex)?

A base 16 number system using 0-9 and A-F.

How do you convert binary to hex?

Group bits into 4-bit chunks and convert each group to hex.

Convert 10101110 to hex.

1010 1110 → AE.

What are the two parts of a floating-point number?

Mantissa and Exponent.

What is the purpose of normalisation?

To ensure maximum precision by adjusting the mantissa and exponent.

How do you normalise a floating-point number?

Adjust the number so it starts with 01 (positive) or 10 (negative).

What are the three types of bitwise operations?

Shifts, AND/OR/XOR, Masks.

What does a left shift do?

Multiplies a number by 2^n.

What does a right shift do?

Divides a number by 2^n

What is a mask?

A binary pattern used to extract or modify specific bits.

What are the two main character sets?

ASCII and Unicode.

How many bits does ASCII use?

7 bits, representing 128 characters.

Why was Unicode introduced?

To support multiple languages and more characters.

How many bits does Unicode use?

Variable length (16-bit, 32-bit, etc.).