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Linux, the free operating system that Linus Torvalds started in 1991 as a 21-year-old student in Helsinki, can be used and changed by anyone. Since November 2017 it has run every machine on the TOP500 list of the world's fastest supercomputers.

Linus Torvalds, 1991

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On 25 August 1991 Torvalds announced his project in an online discussion group, describing a free operating system that was ‘just a hobby’. Strictly, Linux is a kernel: the core of an operating system, which manages the processor, memory and devices so that other programs can run. Torvalds wanted to call it Freax, but Ari Lemmke, who helped run the Finnish university network's server where the files were first shared, named the folder Linux, and the name stuck. In 1992 Torvalds released it under the GNU General Public License, which lets anyone use, study, change and share the code as long as their changed versions stay free too. Thousands of volunteers and companies now work on it. The Linux kernel runs inside every Android phone and on much of the internet's servers.

Türkçe oku
Ücretsiz işletim sistemi Linux'u, 1991'de Helsinki'de 21 yaşında bir üniversite öğrencisi olan Linus Torvalds başlattı. Herkes onu kullanabilir ve değiştirebilir. Kasım 2017'den bu yana, dünyanın en hızlı süper bilgisayarlarını sıralayan TOP500 listesindeki makinelerin hepsi Linux'la çalışıyor.

Torvalds 25 Ağustos 1991'de projesini internetteki bir tartışma grubunda duyurdu ve yazdığı ücretsiz işletim sisteminin “sadece bir hobi” olduğunu söyledi. Linux aslında bir çekirdektir, yani işletim sisteminin işlemciyi, belleği ve donanımı yöneterek öteki programların çalışmasını sağlayan temel parçası. Torvalds ona Freax adını vermek istiyordu, ama dosyaların ilk paylaşıldığı Fin üniversite ağı sunucusunun yöneticilerinden Ari Lemmke klasöre Linux adını verdi ve bu ad tuttu. Torvalds 1992'de kodu GNU Genel Kamu Lisansı'yla yayımladı. Bu lisans, değiştirilmiş sürümler de özgür kaldığı sürece herkesin kodu kullanmasına, incelemesine, değiştirmesine ve paylaşmasına izin verir. Bugün Linux'u binlerce gönüllü ve şirket geliştiriyor. Linux çekirdeği her Android telefonun içinde çalışıyor, internet sunucularının da büyük bölümü ona dayanıyor.

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WonderHistory

When Neil Armstrong radioed “Houston, Tranquility Base here. The Eagle has landed” on 20 July 1969, his words reached Earth about 1.3 seconds later. Radio waves travel at the speed of light, and the Moon is about 384,000 km (239,000 miles) away.

Eagle was the lunar module that carried Armstrong and Buzz Aldrin down to the surface. Light, and so radio, travels at almost 300,000 km per second. At the Moon's average distance of about 384,400 km, a signal takes roughly 1.28 seconds each way, so every exchange with Mission Control in Houston had a built-in pause of about 2.6 seconds before an answer could arrive. Large dish antennas at Goldstone in California and at Honeysuckle Creek and Parkes in Australia picked up the signals; the clearest pictures of the first steps came through Australia and were watched live by an estimated 600 million people. Before leaving, the crew set up a panel of reflectors on the surface. Scientists still fire lasers at it and time the light's return, which is how we know the Moon is drifting away from Earth by about 3.8 cm a year.

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WonderTechnology

The Apollo Guidance Computer that steered astronauts to the Moon had about 4 kilobytes of rewritable memory and 72 kilobytes of permanent memory. Its programs were woven by hand into “rope memory”: a wire threaded through a tiny magnetic ring stored a 1, and a wire passing it by stored a 0.

Designed at the MIT Instrumentation Laboratory and built by Raytheon, the computer was one of the first to use silicon chips (integrated circuits) and fitted into about 28 litres. Its memory was counted in “words” of 16 bits, or binary digits: 2,048 rewritable and 36,864 permanent. During Apollo 11's descent on 20 July 1969 it flashed 1202 and 1201 alarms: a radar left on in case the landing had to be abandoned was stealing processing time and overloading it. Its operating system, designed by J. Halcombe Laning, dropped less urgent jobs and restarted in a moment while the landing programs kept running, so Mission Control told the crew to carry on. The flight software was written by a team led by Margaret Hamilton, who received the Presidential Medal of Freedom in 2016. Its power was similar to that of the first home computers of the late 1970s.

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WonderTechnology

The Antikythera mechanism, an ancient Greek geared device probably made in the 2nd century BC, had a spiral dial covering 223 lunar months for predicting eclipses. Symbols on the dial marked the months when an eclipse of the Sun or Moon was expected, and inscriptions gave details such as the hour.

Sponge divers found the mechanism in 1901, a corroded lump among treasures from a Roman-era ship that sank off the Greek island of Antikythera around 70 to 60 BC. Its hand-turned bronze gears modelled the movements of the Sun and Moon, and it is called the oldest known analogue computer, a machine that calculates with moving parts rather than digits. The eclipse dial follows the Saros cycle: after 223 lunar months (new moon to new moon), about 18 years and 11 days, the Sun, Earth and Moon return to almost the same positions, so eclipses repeat in a similar pattern. Symbols in 51 of the dial's cells mark 38 lunar and 27 solar eclipses. Much of this was read only in the 2000s, when researchers including Mike Edmunds and Tony Freeth used X-ray scans to see inside the fragments. The front, which probably showed the planets, is largely lost.

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WonderTechnology

Paper money was first used in China. In the early 11th century, merchants in Sichuan began issuing paper notes called jiaozi in place of heavy iron coins, and in 1023 the Song government took over issuing them. Europe's first banknotes appeared in Sweden in 1661.

The idea had roots in the Tang dynasty (618–907): by 804, merchants were using “flying cash”, paper certificates that let them move money across China without carrying coins. In Sichuan, where iron coins were too heavy for large payments, private firms in the regional capital, Chengdu, began issuing jiaozi notes. When some issuers went bankrupt, the state set up its own office in 1023 and printed the first government notes the following year. Paper money rested on trust: a note was worth only what its issuer promised. That trust could be abused, and when the Song printed far more notes than they could back with coins, prices soared. Europeans learnt of paper money from travellers such as Marco Polo, who described the Mongol emperor Kublai Khan's notes in the 13th century. Europe's first banknotes came from Stockholms Banco in 1661; the bank failed six years later.

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WonderTechnology

The magnetic compass began in China as a tool for fortune-telling and geomancy, the art of siting houses and tombs in harmony with the land. The first records of Chinese sailors steering by a magnetised needle date from the early 12th century.

The first Chinese direction-finders were probably “south-pointing spoons” made of lodestone, a naturally magnetic iron ore. Placed on a smooth bronze board marked with directions, the spoon turned until its handle pointed south. Texts from the Han dynasty (206 BC to AD 220) appear to describe such devices, although archaeologists have not yet found one. The big step came under the Song dynasty. In 1088 the scholar Shen Kuo described needles magnetised by rubbing them on lodestone, and noticed that they do not point exactly north-south, the effect now called magnetic declination. A few decades later the writer Zhu Yu recorded that sailors steered by the stars at night and the sun by day, and turned to the south-pointing needle when the sky was overcast. In Europe, the first written mention of a compass dates from about 1190.

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