Data Representation

What Data Representation covers

Data Representation is examined in Paper 2, Computing concepts. It covers number bases and why hexadecimal is used, converting between binary, decimal and hexadecimal, units of information: bits, bytes and prefixes, binary addition and binary shifts, character encoding: ASCII and Unicode, pixels, bitmaps and colour depth, bitmap image file size calculations, digital sound: sampling rate and sample resolution and data compression: Huffman coding and run-length encoding.

The 9 subtopics

Each one has its own page.

• Number bases and why hexadecimal is usedDecimal, binary and hexadecimal, the values of A to F, place values in binary and hex, why computers work in binary, and why programmers read data in hexadecimal.Open →
• Converting between binary, decimal and hexadecimalStep-by-step methods and worked conversions between binary, decimal and hexadecimal, checking an answer, the largest value one byte holds, and a common conversion mistake explained.Open →
• Units of information: bits, bytes and prefixesBits and bytes, the prefixes kilo, mega, giga and tera, why some count a kilobyte as 1,024 bytes, and conversions between units including how many photos fit on a card.Open →
• Binary addition and binary shiftsThe rules for adding binary digits, worked additions of two and three numbers, overflow beyond 255, and left and right logical shifts as multiplication and division by powers of two.Open →
• Character encoding: ASCII and UnicodeCharacter sets and codes, 7-bit ASCII and the order of its codes, working out a letter's code from A = 65, why '5' differs from 5, and why Unicode was needed.Open →
• Pixels, bitmaps and colour depthPixels, image size and colour depth, how many colours a given depth can show, how more pixels or bits change an image, and decoding short rows of bitmap data.Open →
• Bitmap image file size calculationsThe file size formula for bitmaps, worked calculations in bits, bytes, kilobytes and megabytes, working backwards to a width or colour depth, and how resizing changes storage.Open →
• Digital sound: sampling rate and sample resolutionAnalogue and digital data, how sound is sampled, sampling rate and sample resolution and their effect on quality, the file size formula, and worked sound file calculations.Open →
• Data compression: Huffman coding and run-length encodingWhy data is compressed, lossy and lossless compression, building and reading Huffman codes, bits saved against 7-bit ASCII, and run-length encoding with worked pairs.Open →

What you need to know

Answer each one before you reveal it.

Take Data Representation further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Bit vs Byte

  Bit: a single binary digit that is either 0 or 1. Byte: a group of eight binary digits.

• Left shift vs Right shift

  Left shift: moving every bit towards the most significant end, doubling the value per place. Right shift: moving every bit towards the least significant end, halving the value per place.

• ASCII vs Unicode

  ASCII: a 7-bit character set of 128 codes covering English letters, digits and punctuation. Unicode: a character set covering the alphabets and symbols of almost every written language.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is a number base?

   Model answer

   A number base is the number of different digits a counting system uses. Each place in a number is worth the base times the place to its right.

2. 2

   What is the base of the decimal system, and which digits does it use?

   Model answer

   Decimal is base 10. Decimal uses the ten digits 0 to 9.

3. 3

   Which digits does binary use?

   Model answer

   Binary is base 2 and uses only the digits 0 and 1. Each binary digit is called a bit.

4. 4

   Which symbols does hexadecimal use?

   Model answer

   Hexadecimal is base 16. Hexadecimal uses the digits 0 to 9 followed by the letters A to F.

5. 5

   Why does hexadecimal need the letters A to F?

   Model answer

   Base 16 needs sixteen single symbols, but there are only ten numerals. The letters A to F stand for the values 10 to 15.

6. 6

   State the decimal values of the hexadecimal digits A to F.

   Model answer

   A is 10, B is 11 and C is 12. D is 13, E is 14 and F is 15.

What is inside Levo

Six ways to work the same material.

Data Representation revision questions

What does Data Representation cover in AQA GCSE Computer Science?

9 subtopics: number bases and why hexadecimal is used, converting between binary, decimal and hexadecimal, units of information: bits, bytes and prefixes, binary addition and binary shifts, character encoding: ascii and unicode, pixels, bitmaps and colour depth, bitmap image file size calculations, digital sound: sampling rate and sample resolution and data compression: huffman coding and run-length encoding. Each one has its own page with questions and model answers.

How is Data Representation organised?

By the AQA 8525 specification, subtopic by subtopic, so it matches the order you are taught it in.