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Another memory trick to calculate the allowed downtime duration for an "-nines" availability percentage is to use the formula seconds per day. For example, 90% ("one nine") yields the exponent 4 − 1 = 3 {\displaystyle 4-1=3} , and therefore the allowed downtime is 8.64 × 10 3 {\displaystyle 8.64\times 10^{3}} seconds per day.
Uptime is a measure of system reliability, expressed as the period of time a machine, typically a computer, has been continuously working and available. Uptime is the opposite of downtime. Htop adds an exclamation mark when uptime is longer than 100 days.
For example, a percentage of 99.5% could be expressed as "two nines five" (2N5, or N2.5) [2] or as 2.3 nines, [citation needed] following from the logarithm definition. A percentage of 100% would, in theory, have an infinite number of nines – though, in the context of purity of materials, 100% is virtually unachievable.
[1] [citation needed] In early days of computing, availability was not considered business critical. With the increasing use of mobile computing, global access to online business transactions and business-to-business communication, continuous availability is increasingly important based on the need to support customer access to information ...
In an increasing system, the time constant is the time for the system's step response to reach 1 − 1 / e ≈ 63.2% of its final (asymptotic) value (say from a step increase). In radioactive decay the time constant is related to the decay constant ( λ ), and it represents both the mean lifetime of a decaying system (such as an atom) before it ...
The term "second" comes from "the second minute division of an hour", as it is 1 ⁄ 60 of a minute, or 1 ⁄ 60 of 1 ⁄ 60 of an hour. While usually sub-second units are represented with SI prefixes on the second (e.g. milliseconds ), this system can be extrapolated further, such that a "Third" would mean 1 ⁄ 60 of a second (16.7 ...
A simple example arises where the quantity to be estimated is the population mean, in which case a natural estimate is the sample mean. Similarly, the sample variance can be used to estimate the population variance. A confidence interval for the true mean can be constructed centered on the sample mean with a width which is a multiple of the ...
A mathematical constant is a key number whose value is fixed by an unambiguous definition, often referred to by a symbol (e.g., an alphabet letter), or by mathematicians' names to facilitate using it across multiple mathematical problems. [1]