2.1.4 Data Representation Units

Data representation - Units Candidates should be able to: Define the term bit, nibble, byte, kilobyte, megabyte, gigabyte, terabyte Understand that data needs to be converted into a binary format to be processed by a computer

Data and Information Data is any collection of numbers, characters or other symbols that has been coded into a format we can input into a computer and process. Data on its own has no meaning, or context. It is only after processing by a computer that data takes on a context and becomes information.

There are many types of data All data ends up being stored as a series of numbers inside the computer. Data can be inputted into the computer by the user in many different ways. The main types of data we input into a computer which gets processed are numbers, text, dates, images and sound.

Units Bit, Nibble, Byte Bit (Binary Digit) is the smallest unit of data that can be stored. Each bit is represented as a binary number, either 1 (true) or 0 (false). Byte contains 8 bits. Could be stored as 11101001. A single keyboard character such as letter A, takes up one byte of storage. Nibble is not commonly used as groups of 8 bits and higher are most common. Used for a group of four bits so two nibbles make a byte.

Kilobyte Unit of storage which can be written as kB or kbyte. Thought of as 1,000 bytes but is actually 1,024 bytes which is 2 to the power of 10. Equivalent to 1024 characters on the screen. Megabyte Unit of storage which can be writted as MB or mbyte. Thought of as one million bytes or 1,000 kilobytes but is actually 1,048,576 bytes or 1,024 kilobytes. Typical MP3 song can be between 3 to 5 megabytes in size. CD can store 650 megabytes of data.

Gigabyte Can be written as GB or gbyte. Thought of as 1,000 megabytes but is actually 1024 megabytes. A DVD can hold a film which would be around 4-8 gigabytes in size. Hard disks are in gigabytes with a typical on being 160GB. Terabyte Can be written as TB. Commonly seen as 1,000GB but is actually 1024 GB. Equivalent to just over one million megabytes. Could hold about 300 hours of good quality video.

Binary data Analogue data is processed by humans, it is data on a continuous scale. E.g. temperature in the classroom going down in stages from 20 C to 19.9 C etc. Computers can only process digital data, 1s and 0s and binary data. So data from the outside world needs to be converted into binary numbers before the computer can process it. This is done by a piece of hardware called an analogue-to-digital converter (ADC) Analogue data = time, height, noise levels, acidity etc.

Converting a denary number into a binary number We use a ‘Denary’ number system in our everyday lives which has the number digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. This is called a ‘base-10’ number system. Examples are 5, 24, 316, 8715. Computers use binary numbers to process data. There are only two digits, 1 and 0. This is called a ‘base-2’ number system. Examples are 1, 101, 1101, 11011001.

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