OCR GCSE Computer Science - Memory and Storage

Comprehensive vocabulary flashcards based on Section 1.2 Memory and Storage concise notes for OCR GCSE Computer Science.

RAM (Random Access Memory)

Holds the operating system, running applications, and associated data while the computer is on and in use; it is volatile, temporary, and can be read from and written to.

ROM (Read-only Memory)

Stores the bootstrap loader/BIOS to start the computer from scratch; it is non-volatile, permanent, and read-only during normal operation.

Volatile Memory

Memory that loses its stored data when the power is turned off.

Non-volatile Memory

Memory that retains its stored data even when the power is turned off.

Virtual Memory

A portion of secondary storage used as an extension of RAM when there is insufficient RAM, moving data not currently needed by the CPU from RAM to secondary storage and retrieving it back when required.

Secondary Storage

Non-volatile storage needed to store files and programs; it must be low cost, high capacity, and reliable.

Magnetic Storage

Storage technology that mostly uses hard disk drives (HDDs) made of a stack of rotating magnetic disks (platters) and a moving read/write head.

Solid-state Storage

Storage technology using flash memory with no moving parts, making access faster, power requirements low, and generating no noise or heat.

Optical Storage

Storage devices (such as CDs, DVDs, and Blu-Ray disks) that work by reflecting laser light onto the surface of a rotating disk and reading reflections as 1s or 0s.

Nibble

A unit of data storage equal to $4\text{ bits}$.

Byte

A unit of data storage equal to $8\text{ bits}$.

Kilobyte (KB)

A unit of data storage equal to $1000\text{ bytes}$.

Megabyte (MB)

A unit of data storage equal to $1000\text{ KB}$.

Gigabyte (GB)

A unit of data storage equal to $1000\text{ MB}$.

Terabyte (TB)

A unit of data storage equal to $1000\text{ GB}$.

Petabyte (PB)

A unit of data storage equal to $1000\text{ TB}$.

Sound File Size Formula

$$\text{sound file size} = \text{sample rate (Hz)} \times \text{duration (s)} \times \text{bit depth}$$

Image File Size Formula

$$\text{image file size} = \text{colour depth} \times \text{image height (pixels)} \times \text{image width (pixels)}$$

Text File Size Formula

$$\text{text file size} = \text{bits per character} \times \text{number of characters}$$

Left Shift

A binary shift operation that is equivalent to multiplying a binary number by $2$.

Right Shift

A binary shift operation that is equivalent to dividing a binary number by $2$.

Overflow Error

An error that may happen when adding together two binary numbers when there is a carry bit or leftover bit.

Most Significant Bit (MSB)

The leftmost digit in a binary number; in an $8\text{-bit}$ number, the MSB value represents $128$ in decimal.

Least Significant Bit (LSB)

The rightmost digit in a binary number; in an $8\text{-bit}$ number, the LSB value represents $1$ in decimal.

Character Set

A list of all the characters available to a computer.

ASCII

A $7\text{-bit}$ character code capable of representing the English alphabet, numbers, some symbols, and some control characters, with $2^7$ or $128$ characters available.

Extended ASCII

An $8\text{-bit}$ character code that uses the 8th bit in the byte to include extra symbols, mathematical symbols, and non-English characters, with $2^8$ or $256$ characters available.

Unicode

A character encoding standard that originally used a $16\text{-bit}$ code ($2^{16}$ or $65536$ characters available) to represent non-English characters and symbols, extended to represent billions of characters.

Pixel

Individual picture units forming an image on screen, stored as binary codes where the number of bits per pixel determines available colours.

Image Metadata

Information stored with an image telling the computer how to reproduce it from binary data, including colour depth, resolution, geographical data, date created, date modified, and file size.

Colour Depth

The number of bits used per pixel in an image.

Resolution

The number of dots (pixels) per unit of distance, for example dots per inch (DPI).

Sample Rate

The number of samples taken per second when converting analogue sound to digital, measured in $\text{Hz}$ (hertz).

Duration

The length of time that a sound is sampled for, measured in seconds or minutes.

Bit Depth (Sound)

The number of bits used to store each audio sample.

Lossy Compression

A data compression method where some data is removed to make the file smaller, and the original file cannot be restored; suitable for images and video.

Lossless Compression

A data compression method where no data is removed, algorithms look for patterns so repeated data is stored once, and the original file can be fully restored; suitable for text files and audio.