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

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. In this system, "five nines" equals 0.99999 (or 99.999%) availability.

Availability of a system is typically measured as a factor of its reliability - as reliability increases, so does availability. However, no system can guarantee 100.000% reliability; and as such, no system can assure 100.000% availability. Further, reliability engineering and maintainability involve processes designed to optimize availability under a set of constraints, such as time and cost-effectiveness. Availability is the goal of most system users, and reliability engineering and maintainability provide the means to assure that availability performance requirements are achieved.

El Mariachi is a 1992 American action film that is the debut of writer/director Robert Rodriguez. The Spanish language film was shot in the northern Mexican bordertown of Ciudad Acuña with a mainly amateur cast. The US$7,000 production was originally intended for the Mexican home video market, but executives at Columbia Pictures liked the film so much that they bought the American distribution rights. Columbia eventually spent several times more than the 16 mm film's original budget on 35 mm transfers, promotion, marketing and distribution.

The success of Rodriguez's directorial debut led him to create two further entries, Desperado (1995) and Once Upon a Time in Mexico (2003), in what came to be known as the Mexico Trilogy. In 2011, the film was inducted into the Library of Congress to be preserved as part of its National Film Registry for being culturally, historically, or aesthetically significant.

In a small Mexican town, a ruthless criminal, nicknamed Azul (Reinol Martínez), breaks out of jail and vows revenge on the local drug lord, Moco (Peter Marquardt), who put him there in the first place, by using a guitar case which carries a small arsenal of guns. At the same time, a young mariachi (Carlos Gallardo) arrives in the town looking for work, carrying his guitar case with his signature guitar.