Mean Time To Failure (MTTF)
MTTF is a basic measure of reliability for non-repairable
systems. It is the mean time expected until the first failure
of a piece of equipment. MTTF is a statistical value and
is meant to be the mean over a long period of time and large
number of units.
For constant failure rate systems, MTTF is the inverse
of the failure rate. If failure rate is in failures/million
hours, MTTF = 1,000,000 / Failure Rate for components with
Technically MTBF should be used only in reference to repairable
items, while MTTF should be used for non-repairable items.
However, MTBF is commonly
used for both repairable and non-repairable items.
more information: http://www.i-mtbf.com/