The basic unit used in computer data storage is called a bit (binary digit). Computers use these little bits, which are composed of ones and zeros, to do things and talk to other computers. All your files, for instance, are kept in the computer as binary files and translated into words and pictures by the software (which is also ones and zeros). This two number system, is called a “binary number system” since it has only two numbers in it. The decimal number system in contrast has ten unique digits, zero through nine.
Although computer data and file size is normally measured in binary code using the binary number system (counted by factors of two 1, 2, 4, 8, 16, 32, 64, etc), the prefixes for the multiples are based on the metric system! The nearest binary number to 1,000 is 2^10 (2 to the 10th power) or 1,024; thus 1,024 bytes was named a Kilobyte. So, although a metric “kilo” equals 1,000 (e.g. one kilogram = 1,000 grams), a binary “Kilo” equals 1,024 bytes (e.g. one Kilobyte = 1,024 bytes).
Since writing out a formula on packaging for hard drives, discs, SD cards and USB flash drives would be really hard, it become the convention, many years ago, to use the MB and GB system instead of trying to denote how many bits or even bytes there are. This means there are 1,028,718,592 bytes for a 1GB capacity drive. But you have to divide that number by 1024 (or 2^10) three times. This is moving up the scale from Bytes, to Kilobytes, to Megabytes and finally, the actual capacity of Gigabytes = .958GB. Simply, there will always be more bytes than the listed GB or MB number.
Here is a simple exercise to demonstrate the difference. Click “Computer” on a Windows computer. Right click the “Local Disc” and select “Properties” in the pop-up menu (usually the last option). In the “General” tab you should see a pie chart. But above the pie chart is a line that states “Capacity” and it gives you two numbers, a long one in bytes and a short one in GB. This is how your computer reads the difference. Your computer used the binary system to divide the large number by 1024 (or 2^10) three times to get the GB number!
(By C. Smith · Tuesday, February 26th, 2013)