K

One thousand. A computer whose memory has a capacity of 64K can store 64,000 bits of information. (Actually, for reasons too complicated too explain, 64K equals 65,536 bits.)

More Detailed Definition:

In decimal systems, kilo stands for 1,000, but in binary systems, a kilo is 1,024 (2 to the 10th power). Technically, therefore, a kilobyte is 1,024 bytes, but it is often used loosely as a synonym for 1,000 bytes. For example, a computer that has 256K main memory can store approximately 256,000 bytes (or characters) in memory at one time.

A megabyte is 2 to the 20th power (approximately 1 million) and a gigabyte is 2 to the 30th power (approximately 1 billion).

In computer literature, kilobyte is usually abbreviated as K or Kb. To distinguish between a decimal K (1,000) and a binary K (1,024), the IEEE has suggested following the convention of using a small k for a decimal kilo and a capital K for a binary kilo, but this convention is by no means strictly followed.