Unit 2: Data Edexcel GCSE Computer Science

Pixel

The smallest single point of colour in an image

Resolution

The number of pixels in an image. Sometimes identified by the width and height of the image as well as the total number of pixels in the image.

ASCII

A standard for representing characters, using 7 bits - 128 unique characters can be represented

Character set

The list of characters recognised by a computer

Colour depth

The number of bits used to encode the colour of each pixel

Sampling

Measurements taken of a sound wave at regular intervals of time

Fidelity

how accurate the recording is to the original sound.

High fidelity

A very accurate digital recording; often called hi-fi

Compression

Changing the format of a file to decrease the file size

Lossless compression

Compressing a file and not losing any data

Lossy compression

Compressing a file by removing some of the data

Sample rate

The number of samples taken per second, often measured in Kilohertz (kHz)

Sample interval

The distance or time between data points or measurements.

Bitmap

An image composed of pixels with a fixed resolution

Binary

Base 2 Number system using 0 and 1

Hexadecimal

A base-16 number system that uses symbols 0-9 and A-F to represent numbers from 0 to 15.

Byte

8 bits

Nibble

4 bits

Kibibyte (KiB)

1024 bytes

Mebibyte (MiB)

1024 kibibytes

Gibibyte (GiB)

1024 mebibytes

MSB

Most Significant Bit, the left-most bit in a binary whole number or code

Two's complement

A method of being able to store negative numbers as binary digits. It works by turning the MSB into a sign bit, where 0 represents a positive number and 1 represents a negative.

Overflow

Error that results when the number of bits is not enough to represent the number.

Logical Shift Left

(<<)Everything moves left by a bit, and the LSB on the right is filled with a zero - multiplication

Logical Shift Right

(>>)Everything moves right by a bit, and the MSB on the left is filled with a 0 - division

Uses of Hexadecimal

Defining colours in HTML and MAC addresses

Bit depth

The number of bits used to encode each sound sample. (Higher bits → greater quality → larger file size)

Amplitude

Height of an audio wave: larger amplitude = louder sound

Data compression algorithms

Algorithms designed to reduce the number of bits needed to represent a piece of information

Data capacity

The amount of data that can be stored on a secondary storage device or in a computer's memory

MP3

A standard format for audio files

Why is hexadecimal used?

Hexadecimal uses less digits than binary so humans find it easier to read