Availability vs. Disponibility

Availability

In reliability theory and reliability engineering, the term availability has the following meanings:

The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e. a random, time. Simply put, availability is the proportion of time a system is in a functioning condition. This is often described as a mission capable rate. Mathematically, this is expressed as 100% minus unavailability.

The ratio of (a) the total time a functional unit is capable of being used during a given interval to (b) the length of the interval.

For example, a unit that is capable of being used 100 hours per week (168 hours) would have an availability of 100/168. However, typical availability values are specified in decimal (such as 0.9998). In high availability applications, a metric known as nines, corresponding to the number of nines following the decimal point, is used. With this convention, “five nines” equals 0.99999 (or 99.999%) availability.

Availability (noun)

the quality of being able to be used or obtained

“turkey producers had been losing sales because of the all-year-round availability of beef”

“the availability of social housing varies widely in rural areas”

Availability (noun)

the state of being otherwise unoccupied; freedom to do something

“they enquired as to my availability for a game the following evening”

Availability (noun)

the state of not being currently involved in a sexual or romantic relationship

“if you call yourself ‘Miss’ you’re advertising your availability to any man who takes a fancy”