GCSE Computing A451
Unit 4.1 – Units of Data
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Unit 4.1– Units of Data
Candidates should be able to:
a) Define the terms bit, nibble, byte, kilobyte, megabyte, gigabyte, terabyte
b) Understand that data needs to be converted into a binary format to be processed
by a computer.
Units of Data in Computer Systems
Unit
Bit
Nibble
Byte
Kilobyte (KB)
Size
1 bit
4 bits
8 bits
1024 bytes
Unit
Megabyte (MB)
Gigabyte (GB)
Terabyte (TB)
Petabyte (PB)
Size
1024 Kb
1024 MB
1024 GB
1024 TB
•
A bit is the smallest unit of data that a computer uses. It holds a binary value of either 0 or 1.
•
A nibble consists of 4 bits. This means it can store 16 possible binary values, 0000 to 1111.
Example of use: Binary Coded Decimal (BCD) System - 1 nibble is used to encode each digit
e.g.
•
78 -> 0111 1000
251 -> 0010 0110 0001
A byte consists of 8 bits. It can store 256 possible binary values, 00000000 (0) to 11111111 (255).
e.g.
•
29 -> 0010 1001
29 -> 00011101
78 -> 01001110
251 -> 11111011
A kilobyte (KB) consists of 1024 bytes (Sometimes rounded to 1000 MB or 103 bytes).
1KB of memory could store roughly one full A4 page of text.
•
A Megabyte (MB) consists of 1024 Kilobytes (Sometimes rounded to 1000 Kb or 106 bytes).
•
A Gigabyte (GB) consists of 1024 Megabytes (Sometimes rounded to 1000 MB or 109 bytes).
•
A Terabyte (TB) consists of 1024 Gigabytes (Sometimes rounded to 1000 GB or 1012 bytes).
Why does data need to be converted into a binary format to be
processed by a computer?
Computers can only understand 1s and 0s... they process and store binary numbers. Any other type
of data is useless to a computer unless it is first translated into binary form (digitised). This is true
for all text, images, music and data that originate from an analogue (non-digital) source.
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