Software Quality Assurance

317SOFTWARE RELIABILITY AND PROCESS

Mean Time to Failure

Mean time to failure (MTTF) describes the expected time to failure

for a nonrepairable system.

For example, assume that you tested three identical systems starting

from time 0 until all of them failed. e first system failed at 10 hours,

the second failed at 12 hours, and the third failed at 13 hours.

e MTTF is the average of the three failure times, which is

11.6667 hours.

is metric is the basic parameter required by most software reli-

ability models.

High values imply good reliability.

Failure Rate

Used to indicate the growth in the software reliability as a func-

tion of test time.

Usually used with reliability models.

is metric requires two primitives: t

i

is the observed time

between fai ...