One of the more difficult problems you will face when working with computer hardware, especially hard drives, is the two different measurement definitions or terms used to calculate drive capacity. Capacity measurements are usually expressed in kilobytes (thousands of bytes), in megabytes (millions of bytes), or gigabytes (billions of bytes), however, due to a mathematical coincidence there are two different meanings for each of these measures.
Computers are digital, and with that store data using binary numbers, or powers of two, although we are accustomed to using decimal numbers, expressed as powers of ten. As it turns out, two to the tenth power, 2^10, is 1,024, which is very close in value to 1,000 (10^3). Similarly, 2^20 is 1,048,576, which is approximately 1,000,000 (10^6), and 2^30 is 1,073,741,824, close to 1,000,000,000 (10^9). As computer development became more prominent and binary numbers began to be used on a regular basis, computer scientists took note of this similarity and began using the abbreviations normally associated with decimal numbers, and applied them to binary numbers. This led to 2^10 being given the prefix "kilo", 2^20 given the prefix "mega", and 2^30 referred to as "giga".
This shorthand reference works well when used between technicians who regularly work in computer development, as they know what they are referring to, (and no one else really cares). However, when computers entered the mainstream, the dual reference began leading to quite a bit of confusion and inconsistency. In many areas of development, only binary values are used. As an example, 64 MB of RAM memory always means 64 times 1,048,576 bytes, never 64,000,000. Lending confusion to this mess though, in some areas only decimal values are used such as when the term, "56K modem" works at a maximum speed of 56,000 bits per second, not 57,344.
It's no secret that storage devices are the single largest area of confusion in this regard, as some drive manufacturers use the decimal method, while others use the binary method when advertising their drive capacities. Even some software companies play this game, with some software packages using binary megabytes and gigabytes, and others using decimal megabytes and gigabytes. If you are using smaller numbers, the difference between decimal and binary is rather insignificant, but as the numbers grow larger so does the disparity. As an example, there is only a 2.4% difference between a decimal and a binary kilobyte, but when you calculate a megabyte, this difference increases to approximately 5%. A gigabyte produces a difference of approximately 7.5%, which is a rather significant difference. Not too many years ago this difference, as it pertains to hard drives that is, wasn't all that noticeable when drive manufacturers advertised the size of their drives in decimal format, and you partitioned and formatted your drive in binary. Today, however, people are beginning to notice the difference between the two measures. As an example, should you purchase an "80 GB" hard drive, in all probability it will partition and format to about 74.2 to 76.3 gigabytes. Don't worry, there's nothing wrong with the drive, it's just that the manufacturer stated the 80 GB in decimal format, but Windows (MS-DOS) partitioned and formatted the disk in binary gigabytes. There are a few other issues with large hard drive capacities, but we'll address those in the drive limitations and barriers section of this topic area.
Another issue of importance is that of converting between binary gigabytes and binary megabytes. Decimal gigabytes and megabytes differ by a factor of 1,000, however binary measurement differs by 1,024. So the same 80 GB hard disk is 80,000 MB in decimal terms, however the 76.3 binary gigabytes are equal to 78,131 binary megabytes (76.3 times 1,024).......