In the human world, the smallest time element we usually deal with is the second. Rarely do we need to think smaller.

In the computer world, time increments are much smaller and things happen much faster.

• Millisecond. One thousandth (10^-3) of a second. Early PC's typically used times expressed in milliseconds. Some storage devices (e.g., floppy disk drives) still have to use milliseconds due to the speed at which their mechanical elements work.
• Microsecond. One Millionth (10^-6) of a second. Minicomputers and most PC's use times expressed in microseconds.
• Nanosecond. One Billionth (10^-9) of a second. Supercomputers and some PC's use times expressed in nanoseconds.
• Picosecond. One trillionth (10^-12) of a second. A barrier to be broken for most computers.

And, when optical switches start to make their way into computers...

• Femtosecond. One Millionth of a Nanosecond (10^-15). Typically used when dealing with very short laser pulses.
• Attosecond. One Quintillionth (10^-18) of a second. Used when dealing with single photons.

Finally, just for the fun of it, there are a couple of others that are really short...

• Zeptosecond. (10^-21) of a second.
• Yoctosecond. (10^-24) of a second.

The prefixes used above can also be used for units other than seconds. They mean the same thing in terms of 10 to the minus power numbers.

Bits & Bytes