Memory and Storage

What Memory and Storage covers

Memory and Storage is examined in J277/01, Computer systems. It covers RAM, ROM, cache and virtual memory, secondary storage: magnetic, optical and solid state, data units and storage capacity calculations, binary, denary and hexadecimal conversions, binary addition, overflow and binary shifts, character sets, ASCII and Unicode, bitmap images, colour depth and resolution, sound sampling, sample rate and bit depth and lossy and lossless compression.

The 9 subtopics

Each one has its own page.

• RAM, ROM, cache and virtual memoryPrimary storage, the purposes of RAM and ROM, volatile and non-volatile memory, cache and the speed ranking of storage, and how virtual memory works when RAM is full.Open →
• Secondary storage: magnetic, optical and solid stateWhy secondary storage is needed, magnetic, optical and solid state storage, comparing capacity, speed, portability, durability and reliability, and choosing storage for cameras, backups and consoles.Open →
• Data units and storage capacity calculationsBits, nibbles and bytes, units from kilobyte to petabyte, converting between them, fixed capacities, and worked storage calculations including text file sizes.Open →
• Binary, denary and hexadecimal conversionsPlace values and the most and least significant bits, the 0 to 255 range, and worked conversions between binary, denary and hexadecimal with the method for each.Open →
• Binary addition, overflow and binary shiftsThe rules for binary addition, worked additions, overflow errors and how to spot them, and left and right shifts with their effect as multiplication and division.Open →
• Character sets, ASCII and UnicodeHow characters are stored, character sets and bits per character, ASCII and Unicode compared, ordered character codes worked from A = 65, and text file sizes.Open →
• Bitmap images, colour depth and resolutionPixels, colour depth and resolution, how each affects quality and file size, the image file size formula with worked calculations, and why metadata is stored.Open →
• Sound sampling, sample rate and bit depthHow sound is sampled, sample rate, bit depth and duration, their effect on quality and file size, the sound file size formula, and worked calculations.Open →
• Lossy and lossless compressionWhy files are compressed, lossy and lossless compression with their advantages and disadvantages, choosing the right type for spreadsheets, music and X-rays, and common file formats.Open →

What you need to know

Answer each one before you reveal it.

Take Memory and Storage further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• RAM vs ROM

  RAM: volatile working storage holding the programs and data currently in use. ROM: non-volatile storage holding the start-up instructions, which cannot normally be changed.

• Primary storage vs Secondary storage

  Primary storage: memory the CPU accesses directly, holding data and instructions in current use. Secondary storage: non-volatile devices that keep files and programs long term when the power is off.

• Lossy compression vs Lossless compression

  Lossy compression: permanently removing some data so that a file becomes much smaller. Lossless compression: shrinking a file so that the original can be rebuilt exactly.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is primary storage?

   Model answer

   Primary storage is the memory that the CPU can access directly. Primary storage holds the data and instructions currently in use.

2. 2

   Why does a computer need primary storage as well as secondary storage?

   Model answer

   The CPU needs very fast access to the programs and data it is running. Secondary storage is far too slow for the CPU to work from directly.

3. 3

   Which types of memory make up primary storage?

   Model answer

   Primary storage is usually made up of RAM and ROM. Cache is also a form of primary storage.

4. 4

   What does RAM stand for, and what is its purpose?

   Model answer

   RAM stands for random access memory. RAM holds the operating system, programs and data that are currently in use.

5. 5

   What does ROM stand for, and what is its purpose?

   Model answer

   ROM stands for read-only memory. ROM holds the start-up instructions, such as the BIOS, that get the computer running when it is switched on.

6. 6

   What does it mean to say that RAM is volatile?

   Model answer

   Volatile memory loses its contents when the power is switched off. RAM needs a constant power supply to keep its data.

What is inside Levo

Six ways to work the same material.

Memory and Storage revision questions

What does Memory and Storage cover in OCR GCSE Computer Science?

9 subtopics: ram, rom, cache and virtual memory, secondary storage: magnetic, optical and solid state, data units and storage capacity calculations, binary, denary and hexadecimal conversions, binary addition, overflow and binary shifts, character sets, ascii and unicode, bitmap images, colour depth and resolution, sound sampling, sample rate and bit depth and lossy and lossless compression. Each one has its own page with questions and model answers.

How is Memory and Storage organised?

By the OCR J277 specification, subtopic by subtopic, so it matches the order you are taught it in.