J277 1.2 Memory and Storage

Colour depth (also called bit depth)

Refers to how many bits are used to store the colour of each pixel. E.g 2-bit colour depth gives 4 possible colours 00 or 01 or 10 or 11. 3 bit colour depth will give 8 possible colour combinations (2^3 = 8)

Bit depth (Audio bit depth)

Refers to how many bits can be used for each sample. 3 bits means that 8 possible 'levels' (voltages) can be represented. Of course, the more levels you have, the better the quality of the sound. The bit depth on CD is 16 bits (meaning 65536 levels). On DVD it is 24 bits.

Sample rate

Refers to how often samples are taken in a second. It's usually measured in kilohertz (kHz). A common frequency used in MP3s is 44.1 kHz (i.e 44,100 samples per second)

Resolution

Refers to the density of pixels in an image (i.e how many pixels are within a certain area). It is measured in dots per inch (dpi). The higher it is, the better the picture may look, but the file size will be larger.

ASCII

The most commonly used character set in the English speaking world. Each character is given a 8 bit binary code (therefore can only store 256 characters).

Least significant bit (LSB)

The rightmost bit of a binary number that indicates whether it is odd or even. This is because it represents adding 1 or 0 to the final number.

Pixel

The squares that make up an image. Each one is given a binary code which represents the colour of that pixel. The word stands for 'picture element'

Overflow error

This happens when two binary numbers are added together and the result is too big to fit into 8 bits so the calculation is inaccurate.

Metadata

This means 'data about data'. This sounds confusing, but you could also think of it as 'properties' (e.g Resolution, Width, Height, Colour depth etc). It is stored in the same file as the data which it stores the properties of.

Character set

This refers to the amount of characters that a computer recognises. e.g. ASCII or Unicode

Byte (B)

8 bits e.g. 01011100

Kilobyte (KB)

1000 bytes

Terabyte (TB)

1000 gigabytes

Megabyte (MB)

1000 kilobytes

Gigabyte (GB)

1000 megabytes

Petabyte (PB)

1000 terabytes

Analogue

A continually varying wave. It has to be converted into a digital signal for the computer to be able to process it

Binary shift

A fast method of multiplying and dividing a binary number by a power of 2. All bits are shifted to the left or right.

Lossless compression

A form of compression where a special algorithm is used to make the file size smaller but no data is lost (hence the term loss-less). This may happen when using a ZIP utility to compress documents. When you unzip them again, the uncompressed files will be exactly the same as before you compressed them.

Lossy compression

A form of compression where some data is permanently lost when compressing the data. You cannot get back the data afterwards. For example, when saving a high quality image as a lower quality one. The data lost cannot be regained.

Sample

A measurement of the amplitude/height of a wave which is then converted to binary. This happens at regular intervals (e.g. 44.1kHz means 44,100 times per second)

Base 10

A number system that uses 10 possible numbers (012345678&9)

Base 16

A number system that uses 16 possible numbers/letters (0123456789ABCDE&F)

Base 2

A number system that uses 2 possible numbers (0&1)

Left shift

A process performed on a binary number where all the bits move to the left. The remaining bits are filled with 0. This has the effect of multiplying by 2.

Right shift

A process performed on a binary number where all the bits move to the right. The remaining bits are filled with 1. This has the effect of dividing by 2.

File compression

A process which reduces the size of a file (how much storage memory it takes up). This can help with storing files, but is also useful when making transfer of data faster. e.g. Youtube and Netflix will use a lot of compression technologies.

Hex character

A singular Hexadecimal character. E.g D3 is made up of the characters 'D' and '3'

Character

A singular letter, number or symbol. E.g 'A','a','7','!'

Unicode

A universal character set that tries to cover every possible character that might be written in the world. The most common forms are 16-bit (65,536) and 32-bit (4,294,967,296) versions.

Hexadecimal (Hex)

A way of representing a number using numbers from 0-9 and A-F. This is called Base 16 notation because there are 16 possible numbers (0123456789ABCDE&F)

Denary (Decimal)

A way of representing a number using numbers from 0-9. This is called Base 10 notation because there are 10 possible numbers (012345678&9)

Binary

A way of representing a number using only 0s and 1s. This is called Base 2 notation because there are only 2 possible numbers (0&1)

"Describe how binary is used to represent data"

Computers are made up of logic circuits/transistors/switches which use 1 and 0 to show high and low voltage. This enables circuits to be simpler to construct.

Nibble

Half a byte e.g. 1010

Digital

Information (a wave) which can be represented by binary i.e. 1's and 0's

Most significant bit (MSB)

The leftmost bit of a binary number representing the highest power of 2. If you have 4 bits, the leftmost bit represents 8. If you have 8 bits, the leftmost bit represents 128.

Bit (b)

The most basic unit of data in computers. It is either 1 (on) or off (0)