Data

What Data covers

Data is examined in Paper 1, Principles of Computer Science. It covers binary, states and unsigned integers, two's complement, binary addition, overflow and shifts, hexadecimal, ASCII and the limits of binary representation, bitmap images, sound sampling and storage units, file sizes and compression.

The 8 subtopics

Each one has its own page.

• Binary, states and unsigned integersWhy computers use binary, the number of states n bits can represent, unsigned integers from 0 to 255, place values, and worked conversions between denary and binary.Open →
• Two's complementTwo's complement representation, the range −128 to +127, recognising negative values, worked conversions in both directions, and why the CPU uses it.Open →
• Binary addition, overflow and shiftsRules for binary addition, worked 8-bit additions, overflow and its problems, logical left and right shifts, and arithmetic right shifts on negative numbers.Open →
• HexadecimalHexadecimal digits and why programmers use them, why one digit stands for four bits, worked conversions between binary and hexadecimal, and web colours.Open →
• ASCII and the limits of binary representationCharacter sets and 7-bit ASCII, working out codes from A = 65, upper and lower case, the limits of ASCII and Unicode, and the trade-off of using more bits.Open →
• Bitmap imagesPixels, resolution and colour depth, how many colours a given depth allows, the bitmap file size expression, and worked calculations in bytes and KiB.Open →
• Sound samplingHow analogue sound is sampled, amplitude, sample rate, sample interval and bit depth, their effect on quality and size, and worked sound file calculations.Open →
• Storage units, file sizes and compressionBits, nibbles and bytes, kibibytes, mebibytes, gibibytes and tebibytes with worked conversions, and lossless and lossy compression including run-length encoding.Open →

What you need to know

Answer each one before you reveal it.

Take Data further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Logical right shift vs Arithmetic right shift

  Logical right shift: a bit movement that ignores the sign and fills every vacated place with 0. Arithmetic right shift: a bit movement that copies the sign bit into the vacated leftmost places.

• Lossless compression vs Lossy compression

  Lossless compression: a size reduction that lets the original file be rebuilt exactly. Lossy compression: a size reduction that permanently discards detail people rarely notice.

• Mebibyte vs Megabyte

  Mebibyte: a storage unit of exactly 1,048,576 bytes. Megabyte: a storage unit of exactly 1,000,000 bytes.

Questions from this topic

Each one with the model answer underneath.

1. 1

   Why do computers use binary to represent data and program instructions?

   Model answer

   A computer's circuits are built from transistors that act as switches with two states, on and off. The binary digits 1 and 0 map directly onto those two states.

2. 2

   Which kinds of data does a computer store as binary?

   Model answer

   A computer stores numbers, text, sound and images as binary. Program instructions are stored as binary patterns too.

3. 3

   What is a bit?

   Model answer

   A bit is a single binary digit, either 0 or 1. A bit is the smallest unit of data a computer can store.

4. 4

   How many different states can a binary pattern of n bits represent?

   Model answer

   A pattern of n bits can represent 2ⁿ different states. Each extra bit doubles the number of states.

5. 5

   How many different values can a 5-bit pattern represent?

   Model answer

   A 5-bit pattern can represent 32 different values. Five bits give 2⁵ = 32 combinations.

6. 6

   What is the smallest number of bits needed to give a unique code to each of 50 students?

   Model answer

   Six bits are needed, since 2⁶ = 64 codes is enough for 50 students. Five bits give only 32 codes, which is too few.

What is inside Levo

Six ways to work the same material.

Data revision questions

What does Data cover in Edexcel GCSE Computer Science?

8 subtopics: binary, states and unsigned integers, two's complement, binary addition, overflow and shifts, hexadecimal, ascii and the limits of binary representation, bitmap images, sound sampling and storage units, file sizes and compression. Each one has its own page with questions and model answers.

How is Data organised?

By the Edexcel 1CP2 specification, subtopic by subtopic, so it matches the order you are taught it in.