*2.4.2.1 Measurement of availability*

*Maintenance Management*

*2.4.2 Availability*

framework [10]:

independently

must first measure availability.

between failures (MTBF) is displayed as follows.

system (such as waiting time)

different resources. The purpose of this measure is to measure responsiveness and differentiation and differences. Since a system that is well used is generally

3.**Mission capability:** This measure indicates that it is constantly operating in its mission period. Possible measurements may include the distribution of tasks performed during the mission, the availability distance (the system may function successfully during the mission), and the life span (when unacceptable behaviors increase beyond the boundaries of the mandate). This measurement is useful when repair and adjustment are unprofessional or acceptable disastrous behaviors.

4.**Reliability:** This measure determines how long a system will be trusted. Its possible measurement, including MTTF (average failure time) and MTTR (average repair time, long-term availability, and failure cost), is a useful

5.**Efficiency:** This measure determines how a user can effectively perform his work. Possible measurements include friendliness, maintainability, and user comprehension. Because measurement has a problem, it is often overlooked.

The data were presented by Culnan's three dimensions of accessibility as a

1.**Physical dimension:** Access to a terminal and the findings of an existing

3.**Information dimension:** The ability to recover physical information

Relative availability is the time when a system, or a component, should be operational at all when it is expected. A short phrase is that a system can continue to work even when the element or set of elements is gone. To measure reliability we

Most reliability models are also predicted for hardware based on failure fracture rather than failures based on defects. In hardware, failure based on physical (corrosion) is more likely than design failure. The relationship between these key concepts of reliability in hardware and its application for software is specified. If we consider a computer system, a simple measurement of the reliability of the mean time

In a transaction processing system, you may be concerned about system performance that is different from system levels, for example, consider the computer system one, A and the other is B. For the failure type, system A has an average time between two high failure MTTFs and has an average repair time (MTTR), but the failures are because of a large amount of files loss, and the system B has a short MTTF and a high MTTR. But loses of a small amount of data due to failure make user know that B is better than A although MTTF and MTTR and cost criteria may support the system.

and the ability to find a person to help for system use

2.**Communication dimension:** the use of grammatical language to formulate a command including the ability to use the system and its command language

measure when repair is possible and the failure is tolerable.

slower than the responsiveness system is less used.

**102**

According to the theory, Stuart Rance and Hewlett Packard include the following steps:


Use a group of clients that sends known transactions from a point in the network to determine what services are in progress and what they are doing.

According to Stuart Rance and Hewlett Packard, the concept of "user definitive minutes" often measures and reports the number of affected users that is based on multiplying the number of users by the time the system that is out of reach in minutes is being impressed. The number of "user definitive minutes" is often compared with the number of "user potential per minute" to calculate a number for accessibility.

 Availability **∗ 100 =** (user failure minutes **−** user potential minutes)/ (user potential minutes) (1)

Accessibility is an indispensable part of to be considered. It is very necessary to understand what is and how it affects and how it is calculated. Although many methods are proposed to calculate the availability of a device and a simple system, calculating the availability of a business application in a complex organization cannot be easily accessed [11].

#### *2.4.2.2 Different types of accessibility*


regulatory failure, which can lead to preventive and corrective maintenance of the failure.

3.**Operational availability:** When an item works satisfactory, is employed at a point in time and used in a reasonable logic operation and regulatory environment Including logistic time, preparation time, waiting, or regulatory failure.

It both contains corrective and preventive maintenance. Its calculation includes the average time between failures, which is divided by the sum of the average time between failure and the average MDT breakdown. This size defines the availability of elements that are controlled by logistics and extends planners, such as the quality of parts, tools, manpower, and hardware.
