Mainframes

Mainframes are huge and expensive computers used mainly by government institutions and large companies for mission critical applications, usually bulk data processing such as censuses, industry/consumer statistics, ERP, and financial transaction processing.
The term originated during the early 1970s with the introduction of smaller, fewer complex computers such as the DEC PDP-8 and PDP-11 series, which became known as minicomputers or just minis. The industry/users then coined the term "mainframe" to describe bigger, earlier types (previously known simply as "computers").

Water abstraction

Water abstraction, or water extraction, is the procedure of taking water from any source, either temporarily or permanently. Most water is used for irrigation or treatment to produce drinking water. Depending on the environmental legislation in the relevant country, controls may be located on abstraction to limit the amount of water that can be removed. Over abstraction can lead to rivers drying up or the level of groundwater aquifers reducing inappropriately. The science of hydrogeology is used to assess safe abstraction levels.

Allan variance

The Allan variance, named after David W. Allan, is a quantity of stability in clocks and oscillators. It is also identified as the two-sample variance. It is defined as one half of the time average of the squares of the differences between succeed readings of the frequency deviation sampled over the sampling period. The Allan variance depends on the time period used between samples: therefore it is a function of the sample period, as well as the distribution being measured, and is displayed as a graph rather than a single number. A low Allan variance is a characteristic of a clock with good stability over the measured period.

Web proxy

Proxies that hub on WWW traffic are called web proxies. Many web proxies try to block offensive web content. Other web proxies reformat web pages for an exact purpose or audience (e.g., cell phones and PDAs or persons with disabilities). Network operators can also set up proxies to intercept computer viruses and other hostile content served from remote web pages.

Many organizations — including schools, corporations, and countries — use proxy servers to implement acceptable network use policies or to provide security, anti-malware and/or caching services. A traditional web proxy is not translucent to the client application, which must be configured to use the proxy (manually or with a configuration script). In some cases, where substitute means of connection to the Internet are available ,the user may be able to avoid policy control by simply resetting the client configuration and bypassing the proxy. Furthermore administration of browser configuration can be a load for network administrators.