Operating system makers like Microsoft and Apple use a binary system to measure kilobyte, megabytes and gigabytes. Under this scheme, a kilobyte is made up of 1,024 (210) bytes, a megabyte is made up of 1,048,576 (220) bytes, a gigabyte made up of 1,073,741,824 (230) bytes and a terabyte made up of 240 bytes.
Hard drive manufacturers on the other hand use the decimal system for calculating the number of bytes that go to make a kilobyte, megabyte, gigabyte and tebibyte - 1,000 (103), 1,000,000 (106), 1,000,000,000 (109) and 1,000,000,000,000 (1012) respectively. The upshot of all this is that for every gigabyte fitted as storage to a PC, when this is measured by Windows or Mac OS, the customer gets 74 megabytes less than they expect to see, it is same When the operating system caculates that capacity in Gigabytes it divides the 1,000,000,000,000 bytes by 1,073,741,824 bytes/gigabyte which equals 931.3 gigabytes. - that is almost 70GB short of what most people expect to see.
| SI prefixes (Hard Drive) |
equivalent |
Binary prefixes (OS) |
equivalent |
| 1 TB (Terabytes) |
1 * 10004 B |
0.9095 TiB (Tebibytes) |
0.9095 * 10244 B |
| 1000 GB (Gigabytes) |
1000 * 10003 B |
931.3 GiB (Gibibytes) |
931.3 * 10243 B |
| 1,000,000 MB (Megabytes) |
1,000,000 * 10002 B |
953,674.3 MiB (Mebibytes) |
953,674.2 * 10242 B |
| 1,000,000,000 KB (Kilobytes) |
1,000,000,000 * 1000 B |
976,562,500 KiB (Kibibytes) |
976,562,500 * 1024 B |
| 1,000,000,000,000 B (bytes) |
- |
1,000,000,000,000 B (bytes) |
- |
The confusion goes deeper than just hard drives. While CD capacities are given in binary units, DVDs are measured in decimal units.
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