Binary Prefixes (Cambridge (CIE) A Level Computer Science) : Revision Note
Binary prefixes
What is a binary prefix?
A binary prefix is a unit prefix used to indicate multiples of bytes in binary
Consider the word kilobyte, "kilo" is the prefix
Bytes are the smallest unit of data that can be stored in a computer so there needs to be a way of expressing bytes in larger multiples
Denary prefixes
A common way of expressing multiples of bytes is to use denary prefixes:
Denary unit | Equivalent size (bytes) |
|---|---|
1 kilobyte (1 KB) | 1000 |
1 megabyte (1 MB) | 1 000 000 |
1 gigabyte (1 GB) | 1 000 000 000 |
1 terabyte (1 TB) | 1 000 000 000 000 |
1 petabyte (1 PB) | 1 000 000 000 000 000 |
This system relies on the assumption that 1 kilo = 1000
This assumption is based on the denary (base 10) number system
E.g. a 1 GB hard drive can store 1 x 109 bytes
Binary prefixes
However, computers use the binary (base 2) number system so the denary system is technically inaccurate when describing storage
To be precise, expressing multiples of bytes is done using binary prefixes:
Binary unit | Number of bytes (base 2) | Equivalent size (base 10) |
|---|---|---|
1 kibibyte (1 KiB) | 210 | 1024 |
1 mebibyte (1 MiB) | 220 | 1 048 576 |
1 gibibyte (1 GiB) | 230 | 1 073 741 824 |
1 tebibyte (1 TiB) | 240 | 1 099 511 627 776 |
1 pebibyte (1 PiB) | 250 | 1 125 899 906 842 624 |
Notice the prefixes change depending on the system being used, e.g. kilo (denary) vs kibi (binary)
Why does it matter?
The importance of the system being used depends on how precise you need to be
Identifying the total amount of memory (RAM) available to a computer must be accurate (use binary prefixes)
E.g. 16 GiB RAM can store 16 x 230 bytes of data (64 719 476 736 bytes)
when describing storage space, a rough estimate is acceptable (use denary prefixes)
E.g. a 16 GB memory stick can store 16 x 109 bytes of data (16 000 000 000 bytes)
You've read 0 of your 5 free revision notes this week
Unlock more, it's free!
Did this page help you?
