An Explanation of Computer Measurements
NOTE: There are multiple Measuring Systems used in computers. Do not be surprised if you come across some that are slightly different to the ones I describe.
To begin, we need to look at the smallest piece of information a computer can deal with. A piece of Computer Memory can be either a One or a Zero, and this is referred to as a “bit (b)”.
Eight “bits” makes up a “Byte (B)”. This is a useful measure, as it is enough to store one Character (e.g. the letter “a” takes up a Byte. The word “Byte” takes four Bytes (one Byte per letter), and so on).
In the early days of computing, it was decided that a useful measure would be the KiloByte. S.I. Units work with multiples of 1,000, but to keep in fitting with the Binary working of computers, it was chosen that a KiloByte was 1,024 Bytes. That is, 2 to the power of 10 (often expressed as 2^10) Bytes, as Binary numbers are all powers of 2. This was close enough to 1,000 to make it seem useful.
Following the S.I. naming convention, but the Computer numbering convention, the following prefixes are used:
| Prefix | S.I. Measurement | Computer Measurement |
|---|---|---|
| Kilo- | 10^3 = 1,000 | KB = 2^10 = 1,024 |
| Mega | 10^6 = 1,000,000 | MB = 2^20 = 1,048,576 |
| Giga- | 10^9 = 1,000,000,000 | GB = 2^30 = 1,073,741,824 |
| Tera- | 10^12 = 1,000,000,000,000 | TB = 2^40 = 1,099,511,627,776 |
As you can see, there is a small difference between the S.I. Measurement and the Computer Measurement. When we say a kilogram, we mean 1,000 grams, but a kilobyte is 1,024 Bytes, 2.4% different! By the time we get to terabytes (as your hard disk drive may well do), it is nearly 10%!
Most of the time, this will not make any difference to you, and working with “approximately 1,000” is perfectly good enough. Although it is good to know the correct figures.
What you need to know is how much you can store on a hard disk drive, or a memory stick!
| Device | Size | Example Capacity |
|---|---|---|
| Floppy Disk | 1.44MB = 1,500,000 Bytes | 700-1,000 pages of plain text |
| USB Stick | 16 GB = 16,000,000,000 Bytes | 10,000 Photos (average of 1.6MB each) |
| Hard Disk | 1 TB = 1,000 GB = 1,000,000,000,000 Bytes | Over 250,000 .mp3 music files (an average song is about 4MB) |
Older USB Sticks only held 1 or 2 GB of data. While this is a lot compared to Floppy Disks, we didn’t have easy access to Digital Cameras back then! A 1 or 2 GB USB stick will soon fill up!
As you can see, modern storage devices can hold a huge amount of data.