A bit is the storage space needed to store a binary digit -- a $0$ or a $1$. A byte is eight bits -- storage space adequate to store one of the many characters normally encountered on a keyboard (and a few other special characters according to the ASCII character encoding scheme).
We can measure the size of files or hard drives in terms of the number of bytes they can store. However, this can get cumbersome, as the numbers involved are very, very large. So, taking a cue from the metric system, larger units of measure were created by prepending various prefixes to the word "byte". Kilobyte, Megabyte, Gigabyte, etc. are all examples of these. Just a few years ago we were describing hard drive space in terms of Megabytes. Today, Gigabytes is the more common term, with Terabyte starting to reveal its presence. But how much storage does each of these actually describe? This is where it gets interesting, because there is more than one accepted definition for each term.
In the metric system, moving up the scales of units is straight forward. For example, a kilometer is $1000$ meters, a megameter is $1000$ kilometers, a gigameter is $1000$ megameters, and so on... If you are a hard drive manufacturer, this is the standard that is followed. So, for example, a megabyte turns out to be $1,000,000$ bytes. Notice, $1,000,000$ as used here is a decimal number.
However, when the term megabyte is used for real and virtual storage, operating systems and other software often go the more natural binary route, with $1,000,000_2 = 2^{20} = 1,048,576$ bytes intended as the number of bytes described by a megabyte. This means that when you buy an 80 Gigabyte Hard drive you will get a total of 80,000,000,000 bytes of available storage. However, since MS Windows uses the 1,048,576 byte rule, when you look at the Windows drive properties an 80 Gigabyte drive will report a capacity of 74.56 Gigabytes and a 250 Gigabyte drive will only yield 232 Gigabytes of available storage space.
As one moves from the number of bytes in a Kilobyte, to the number of bytes in a Megabyte, and then to the number in a Gigabyte, Terabyte, Petabyte, and beyond -- we can use a multiplier of 1,000 or we can use a multiplier of 1,024. Either choice can be considered "correct". Traditionally, the standards adopted depend on what type of storage is involved.
Processor or Virtual Storage |
Disk Storage |
· 1 Bit = Binary Digit |
· 1 Bit = Binary Digit · 8 Bits = 1 Byte · 1000 Bytes = 1 Kilobyte · 1000 Kilobytes = 1 Megabyte · 1000 Megabytes = 1 Gigabyte · 1000 Gigabytes = 1 Terabyte · 1000 Terabytes = 1 Petabyte · 1000 Petabytes = 1 Exabyte · 1000 Exabytes = 1 Zettabyte · 1000 Zettabytes = 1 Yottabyte · 1000 Yottabytes = 1 Brontobyte · 1000 Brontobytes = 1 Geopbyte |