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4.5 Fundamentals of data representation

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How are signed integers, fractions and binary arithmetic represented?

Understand unsigned and signed binary using two's complement, binary addition and subtraction, fixed point and floating point representation of real numbers, and the effects of overflow and rounding.
A focused answer to AQA A-Level Computer Science 4.5.2 to 4.5.7, covering unsigned and signed binary using two's complement, binary addition and subtraction, fixed and floating point representation of real numbers, and overflow and rounding errors.
9 min answer →

What are bits and bytes, and how are storage capacities measured?

Understand the bit and byte, the units of information capacity, binary and decimal prefixes (kibi versus kilo), and how the number of bits limits the range of values that can be represented.
A focused answer to AQA A-Level Computer Science 4.5.8, covering the bit and the byte, the units of information capacity, binary prefixes (kibi, mebi) versus decimal prefixes (kilo, mega), and how the number of bits limits the range of values.
7 min answer →

How are characters represented as binary using ASCII and Unicode?

Understand character encoding using ASCII and Unicode, the limitations of ASCII, why Unicode was introduced, and the relationship between a character set and a character code.
A focused answer to AQA A-Level Computer Science 4.5.9, covering character encoding using ASCII and Unicode, the limitations of ASCII, why Unicode was introduced, and the relationship between a character set and its codes.
7 min answer →

How is data compressed, encrypted and checked for errors?

Understand lossy and lossless compression, run length encoding and dictionary-based compression, symmetric and asymmetric encryption, and error-checking methods such as parity and check digits.
A focused answer to AQA A-Level Computer Science 4.5.12 to 4.5.14, covering lossy and lossless compression, run length encoding and dictionary-based compression, symmetric and asymmetric encryption, and error checking with parity and check digits.
9 min answer →

What number bases do computers use and how do we convert between them?

Understand the decimal, binary and hexadecimal number systems, why computers use binary and hexadecimal, and how to convert between the three bases.
A focused answer to AQA A-Level Computer Science 4.5.1, covering the decimal, binary and hexadecimal number systems, why computers use binary and hexadecimal, and how to convert between the three bases.
8 min answer →

How are images and sound represented digitally?

Understand how bitmap images are represented using pixels, colour depth and resolution, how analogue sound is sampled, and the effect of sample rate, resolution and metadata on quality and file size.
A focused answer to AQA A-Level Computer Science 4.5.10 and 4.5.11, covering bitmap images with pixels, colour depth and resolution, the sampling of analogue sound, and the effect of sample rate, resolution and metadata on quality and file size.
9 min answer →