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🔗 Computing 🔗 Computer science

In computer science, the five-minute rule is a rule of thumb for deciding whether a data item should be kept in memory, or stored on disk and read back into memory when required. It was first formulated by Jim Gray and Gianfranco Putzolu in 1985, and then subsequently revised in 1997 and 2007 to reflect changes in the relative cost and performance of memory and persistent storage.

The rule is as follows:

The 5-minute random rule: cache randomly accessed disk pages that are re-used every 5 minutes or less.

Gray also issued a counterpart one-minute rule for sequential access:

The 1-minute rule: cache sequentially accessed disk pages that are re-used every 1 minute or less.

Although the 5-minute rule was invented in the realm of databases, it has also been applied elsewhere, for example, in Network File System cache capacity planning.

The original 5-minute rule was derived from the following cost-benefit computation:

BreakEvenIntervalinSeconds = (PagesPerMBofRAM / AccessesPerSecondPerDisk) × (PricePerDiskDrive / PricePerMBofRAM)

Applying it to 2007 data yields approximately a 90-minutes interval for magnetic-disk-to-DRAM caching, 15 minutes for SSD-to-DRAM caching and 2​¹⁄₄ hours for disk-to-SSD caching. The disk-to-DRAM interval was thus a bit short of what Gray and Putzolu anticipated in 1987 as the "five-hour rule" was going to be in 2007 for RAM and disks.

According to calculations by NetApp engineer David Dale as reported in The Register, the figures for disc-to-DRAM caching in 2008 were as follows: "The 50KB page break-even was five minutes, the 4KB one was one hour and the 1KB one was five hours. There needed to be a 50-fold increase in page size to cache for break-even at five minutes." Regarding disk-to-SSD caching in 2010, the same source reported that "A 250KB page break even with SLC was five minutes, but five hours with a 4KB page size. It was five minutes with a 625KB page size with MLC flash and 13 hours with a 4KB MLC page size."

In 2000, Gray and Shenoy applied a similar calculation for web page caching and concluded that a browser should "cache web pages if there is any chance they will be re-referenced within their lifetime."

🔗 Electronics

A Josephson voltage standard is a complex system that uses a superconducting integrated circuit chip operating at a temperature of 4 K to generate stable voltages that depend only on an applied frequency and fundamental constants. It is an intrinsic standard in the sense that it does not depend on any physical artifact. It is the most accurate method to generate or measure voltage and, by international agreement in 1990, is the basis for voltage standards around the world.

🔗 Biography 🔗 Disambiguation

William Adams may refer to:

🔗 India 🔗 India/Indian literature workgroup

The Shishupala Vadha (Sanskrit: शिशुपालवध, IAST: Śiśupāla-vadha, lit. "the slaying of Shishupala") is a work of classical Sanskrit poetry (kāvya) composed by Māgha in the 7th or 8th century. It is an epic poem in 20 sargas (cantos) of about 1800 highly ornate stanzas, and is considered one of the six Sanskrit mahakavyas, or "great epics". It is also known as the Māgha-kāvya after its author. Like other kavyas, it is admired more for its exquisite descriptions and lyrical quality than for any dramatic development of plot. Its 19th canto is noted for verbal gymnastics and wordplay; see the section on linguistic ingenuity below.

🔗 Professional sound production 🔗 Stagecraft

The Schaffer–Vega diversity system (SVDS) was a wireless guitar system developed in 1975–76, engineered and prototyped by Ken Schaffer in New York City, and manufactured by the Vega Corporation, El Monte, California. A handheld microphone version was introduced in 1977.

The system was the first cordless system to be adopted by major rock acts because it solved technical problems common to earlier wireless systems. The reliable sound and freedom of movement it provided paved the way for bands to tour with large multi-level stages in arenas. Schaffer-Vegas were used in the late 1970s and early 1980s by many rock bands such as Pink Floyd (namely guitarist David Gilmour), the Rolling Stones, AC/DC and Kiss.

🔗 International relations 🔗 Ancient Egypt 🔗 Politics 🔗 Sociology 🔗 Asia

A hydraulic empire, also known as a hydraulic despotism, hydraulic society, hydraulic civilization, or water monopoly empire, is a social or government structure which maintains power and control through exclusive control over access to water. It arises through the need for flood control and irrigation, which requires central coordination and a specialized bureaucracy.

Often associated with these terms and concepts is the notion of a water dynasty. This body is a political structure which is commonly characterized by a system of hierarchy and control often based on class or caste. Power, both over resources (food, water, energy) and a means of enforcement such as the military, is vital for the maintenance of control.

🔗 Novels 🔗 Novels/Science fiction 🔗 Science Fiction 🔗 Media franchises

Dune is a science fiction media franchise that originated with the 1965 novel Dune by Frank Herbert and has continued to add new publications up to 2017. Dune is frequently cited as the best-selling science fiction novel in history. It won the 1966 Hugo Award and the inaugural Nebula Award for Best Novel, and was later adapted into a 1984 film and a 2000 television miniseries. Herbert wrote five sequels, and the first two were presented as a miniseries in 2003. The Dune universe has also inspired some traditional games and a series of video games. Since 2009, the names of planets from the Dune novels have been adopted for the real-world nomenclature of plains and other features on Saturn's moon Titan.

Frank Herbert died in 1986. Beginning in 1999, his son Brian Herbert and science fiction author Kevin J. Anderson published a number of prequel novels, as well as two which complete the original Dune series (Hunters of Dune in 2006 and Sandworms of Dune in 2007), partially based on Frank Herbert's notes discovered a decade after his death.

The political, scientific, and social fictional setting of Herbert's novels and derivative works is known as the Dune universe, or Duniverse. Set tens of thousands of years in the future, the saga chronicles a civilization which has banned all forms of computers, or "thinking machines", but has also developed advanced technology and mental and physical abilities. Vital to this empire is the harsh desert planet Arrakis, only known source of the spice melange, the most valuable substance in the universe.

Due to the similarities between some of Herbert's terms and ideas and actual words and concepts in the Arabic language, as well as the series' "Islamic undertones" and themes, a Middle Eastern influence on Herbert's works has been noted repeatedly.

🔗 Military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry 🔗 Classical Greece and Rome 🔗 Military history/Classical warfare

Polybolos, meaning "multi thrower" in Greek, was an ancient Greek repeating ballista reputedly invented by Dionysius of Alexandria, a 3rd-century BC Greek engineer at the Rhodes arsenal, and used in antiquity.

Philo of Byzantium encountered and described a weapon similar to the polybolos, a catapult that like a modern machine gun could fire again and again without a need to reload. Philo left a detailed description of the gears that powered its chain drive, the oldest known application of such a mechanism, and that placed bolt after bolt into its firing slot.

🔗 Physics 🔗 Systems 🔗 Systems/Chaos theory

In condensed matter physics, Hofstadter's butterfly describes the spectral properties of non-interacting two dimensional electrons in a magnetic field. The fractal, self-similar, nature of the spectrum was discovered in the 1976 Ph.D. work of Douglas Hofstadter and is one of the early examples of computer graphics. The name reflects the visual resemblance of the figure on the right to a swarm of butterflies flying to infinity.

The Hofstadter butterfly plays an important role in the theory of the integer quantum Hall effect, and D.J. Thouless has been awarded the Nobel prize in physics in 2016 for the discovery that the wings of the butterfly are characterized by Chern integers, the quantized Hall conductances discovered in 1980 by Klaus von Klitzing for which he has been awarded the Nobel prize in 1985. The colors in the diagram reflect the different Chern numbers.