Basic info: Megabytes, Gigabytes, Terabytes…

These terms are usually used in the world of computing to describe disk space, or data storage space, and system memory. For instance, just a few years ago we were describing hard drive space using the term Megabytes. Today, Gigabytes is the most common term being used to describe the size of a hard drive. In the not so distant future, Terabyte will be a common term. But what are they? This is where it gets quite confusing because there are at least three accepted definitions of each term.



 According to the IBM Dictionary of computing, when used to describe disk storage capacity, a megabyte is 1,000,000 bytes in decimal notation. But when the term megabyte is used for real and virtual storage, and channel volume, 2 to the 20th power or 1,048,576 bytes is the appropriate notation. According to the Microsoft Press Computer Dictionary, a megabyte means either 1,000,000 bytes or 1,048,576 bytes. According to Eric S. Raymond in The New Hacker's Dictionary, a megabyte is always 1,048,576 bytes on the argument that bytes should naturally be computed in powers of two. So which definition do most people conform to?



When referring to a megabyte for disk storage, the hard drive manufacturers use the standard that a megabyte is 1,000,000 bytes. 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. This is where it gets confusing because Windows uses the 1,048,576 byte rule so 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. Anybody confused yet? With three accepted definitions, there will always be some confusion so I will try to simplify the definitions a little.



The 1000 can be replaced with 1024 and still be correct using the other acceptable standards. Both of these standards are correct depending on what type of storage you are referring.

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