OCR J277 · Component 01 · §1.2 · Paper 1

§1.2 Memory and Storage

How is data stored and represented in a computer — from binary to images, and from RAM to hard drives?

Data Representation of Images

Data Representation of Sound

Practice

Where we are · Year 10 · updated 15 September 2026

Covered so far

  • Why data must be binary — bit, nibble, byte
  • The kB → PB ladder and capacity calculations
  • Place value: denary ↔ binary, up to 8 bits
  • Hexadecimal: base 16, and the binary ↔ hex nibble trick
  • Hex in practice — including hex colour codes

This week

  • Binary addition
  • Overflow
  • Binary shifts — left multiplies, right divides

Still to come

  • Characters: character sets, ASCII, Unicode
  • Images: pixels, colour depth, resolution, metadata
  • Sound: sample rate, bit depth, duration
  • Compression: lossy and lossless
  • Primary storage: RAM, ROM, cache, virtual memory
  • Secondary storage: optical, magnetic, solid-state

Quiz — Thursday 17 September. Booklet pp. 2–16, 20 minutes, self-marked.  ·  Unit test — Tuesday 6 October. The whole of §1.2, 37 marks.

Revision

Three explanations of each idea, from three different teachers — if one does not land, try the next. Then practise it.

Units of data storage1.2.3

Bit, nibble, byte, and the kB → PB ladder — then using it to work out how big a file is.

Units of data storageCraig'n'Dave
How to convert between file sizesMr Moore
Data capacity requirementsCSNewbs

Practise2.3 Units — notes and questions CSNewbs

Binary and denary1.2.4

Place value both ways: denary → 8-bit binary, and 8-bit binary → denary.

Converting between denary and 8-bit binaryCraig'n'Dave
How to convert between denary and binaryMr Moore
Denary to binaryCSNewbs

PractiseDenary → binary drill 101 Computing · Binary → denary drill 101 Computing · 2.4a Number systems CSNewbs

Hexadecimal1.2.4

Base 16, and the nibble trick — split eight bits down the middle and read each half.

Converting between denary and 2-digit hexadecimalCraig'n'Dave
Hexadecimal conversionsMr Moore
Binary to hexadecimalCSNewbs

PractiseDenary → hex drill 101 Computing · Hex → denary drill 101 Computing · Binary → hex drill 101 Computing · Hex → binary drill 101 Computing

Binary addition and overflow1.2.4

Adding two 8-bit numbers, carrying, and what happens when the answer will not fit in eight bits.

Adding two 8-bit binary integersCraig'n'Dave
Binary additionMr Moore
Overflow errorsCSNewbs

PractiseBinary addition drill 101 Computing · 2.4b Binary addition and shifts CSNewbs

Binary shifts1.2.4

Left shift multiplies by two, right shift divides by two — and bits fall off the end.

Binary shiftsCraig'n'Dave
Performing a binary shiftMr Moore
Binary shiftsCSNewbs

PractiseBinary shift drill 101 Computing · 2.4b Binary addition and shifts CSNewbs

If you only watch one

1.2 Memory and Storage — full topic revisionMr Moore

Videos remain on their creators' YouTube channels and are embedded, not copied. Practice pages link out to their own sites. Craig'n'Dave · Mr Moore · CSNewbs · 101 Computing.

All data inside a computer is ultimately stored as binary — sequences of 0s and 1s. A bit is the smallest unit; 8 bits make a byte; units scale by 1,000 from there (kilobyte → megabyte → gigabyte → terabyte → petabyte). The same binary digits can represent different things — a number, a character, part of an image — depending on context and encoding. ASCII and Unicode define how characters are encoded; image and sound files are binary sequences whose file size can be calculated from colour depth × resolution and sample rate × duration × bit depth respectively.

Memory sits in a hierarchy. Cache (tiny, very fast) feeds the CPU first; RAM (fast, volatile) holds running programs and data; secondary storage (slow, non-volatile — magnetic, optical, solid-state) holds everything else when the power is off. When RAM is full, the OS moves data to a virtual memory area on secondary storage — slower, but it prevents crashes. The choice of secondary storage type depends on the application: SSDs are fast but expensive; HDDs are slow but cheap and large; optical media (CD/DVD/Blu-ray) is portable but slow.

A 24-bit colour bitmap image has dimensions 1200 × 800 pixels. (a) Calculate the file size in bytes. (b) An audio file is recorded at 44,100 Hz, 16-bit depth, for 3 minutes. Calculate the uncompressed file size in MB. (c) Convert 11011010 from binary to denary. Convert 2D from hex to denary.

Key formulas and facts

Image file size (bits) = colour depth × height (px) × width (px)
Sound file size (bits) = sample rate (Hz) × duration (s) × bit depth
Text file size (bits) = bits per character × number of characters
Units: 1 KB = 1,000 B · 1 MB = 1,000 KB · 1 GB = 1,000 MB · 1 TB = 1,000 GB

What students must understand

Diagrams

Photograph of a RAM memory module
A RAM module. Primary storage is fast and volatile, holding running programs and their data.
Diagram of the surface of an optical disc showing pits and lands and the binary data they encode
Optical storage records data as pits and lands. Each transition between them is read as a 1.
A grid of ones and zeros shown as black and white pixels, illustrating how a bitmap image is stored in binary
A bitmap is just binary. Each pixel's colour is stored as a binary value, here 1 bit per pixel.
An analogue sound wave with sample points marked at regular time intervals
Sampling. The analogue wave is measured at regular intervals, and each sample is stored as a binary number.
The full ASCII character table with decimal and 7-bit binary codes for each character
The ASCII character set. Each character maps to a 7-bit binary code.

Diagrams: PG Online (Paul Long), OCR J277 textbook. Used under the school site licence.

Linking questions

Video Support

Craig'n'Dave — OCR J277
1.2 Memory and storage — unit playlist