Ikigai Daily
Menu
WonderNetwork engineering biography

Radia Perlman, an American engineer, invented the spanning-tree algorithm, which stops data from circling endlessly in computer networks that have duplicate connections. It keeps the spare links switched off and brings one back into use when a cable fails.

Radia Perlman

BiographyTechnologyEngineeringScience

The story behind the card

When a network has more than one path between two points, a message can loop round and round, copying itself until the network jams. Perlman solved this in the mid-1980s while working at Digital Equipment Corporation. Her method lets the switches that connect a network agree among themselves, with no central controller, on one loop-free set of routes shaped like a branching tree; the extra links wait on standby. If a link breaks, the switches recalculate and a standby link takes over. The IEEE, the body behind many networking standards, adopted the method as 802.1D in 1990, and it and its faster successors still keep office and campus networks running. Perlman even described the algorithm in a short poem, “Algorhyme”.

Türkçe oku
Amerikalı mühendis Radia Perlman, yedek bağlantıları olan bilgisayar ağlarında verinin sonsuz döngüye girmesini önleyen “yayılan ağaç” algoritmasını geliştirdi. Algoritma fazladan bağlantıları kapalı tutar; bir kablo koptuğunda bunlardan birini devreye alır.

Bir ağda iki nokta arasında birden fazla yol varsa veri bu yollarda döne döne kendini çoğaltabilir ve sonunda ağ kilitlenir. Perlman bu sorunu 1980'lerin ortasında Digital Equipment Corporation'da çalışırken çözdü. Yöntemi, ağı birbirine bağlayan anahtarların merkezî bir denetçiye gerek duymadan kendi aralarında anlaşmasını ve dallanan bir ağaca benzeyen, döngüsüz tek bir yol düzeni seçmesini sağlar. Fazla bağlantılar yedekte bekler; bir bağlantı koparsa anahtarlar yeniden hesap yapar ve yedeklerden biri devreye girer. Pek çok ağ standardını belirleyen IEEE bu yöntemi 1990'da 802.1D standardı olarak kabul etti. Ofis ve kampüs ağları bugün hâlâ bu yöntemle ya da onun daha hızlı sürümleriyle çalışıyor. Perlman algoritmayı “Algorhyme” adlı kısa bir şiirle de anlatmıştır.

Sources and further reading

Background reading: Radia Perlman
Get the mobile appAbout our cards

Related cards

These cards share a subject or reading mode with the card above.

DriveBiography

Christine Darden, a NASA engineer, wrote computer programs to predict sonic booms, the thunder-like bangs made by aircraft flying faster than sound. Her research showed that reshaping a plane's nose and wings could make them softer on the ground.

Darden, a mathematics graduate of Hampton Institute, joined NASA's Langley Research Center in 1967 as a 'human computer', doing calculations for engineers. She pressed her managers to move her into engineering, and in the 1970s they did. A sonic boom forms when the shock waves from an aircraft's nose, wings and tail merge into one sharp jolt that reaches the ground. Darden's programs modelled those waves and pointed to shapes that keep them from merging, so people below hear a softer thump. She earned a doctorate in engineering from George Washington University in 1983, led NASA's sonic boom team from 1989 and wrote more than 50 papers. NASA's X-59, which first flew on 28 October 2025, was built to test this idea. Her story is also told in Margot Lee Shetterly's book Hidden Figures.

Christine DardenRead card
WonderSpace

A solar sail is a huge, ultra-thin mirror that lets a spacecraft travel on the faint push of sunlight. It needs no fuel, and the tiny push keeps adding speed for as long as light falls on it.

Light has no mass, but it carries momentum, so when it bounces off a mirror it gives it a tiny push. The idea goes back to Johannes Kepler, who noticed in the early 1600s that comet tails point away from the Sun and imagined ships sailing on a heavenly breeze. In 2010 Japan's IKAROS became the first spacecraft to use a solar sail in interplanetary space, on its way past Venus. In 2019 the Planetary Society's LightSail 2, partly funded by public donations, showed that a small satellite could raise its orbit using sunlight alone; it burned up in the atmosphere in 2022. The push is tiny, but it never runs out, so over months it adds up.

Solar sailRead card
DriveSpace

On 26 September 2022, NASA's DART spacecraft deliberately crashed into Dimorphos, a small asteroid orbiting a larger one, and cut the time it takes to circle its partner by about 33 minutes. It was the first proof that an impact can change an asteroid's path.

DART, short for Double Asteroid Redirection Test, launched in November 2021 and hit Dimorphos, about 150 metres across, at roughly 6.1 kilometres per second. Neither Dimorphos nor its partner Didymos was ever a threat to Earth; the pair was chosen because a change in the small asteroid's orbit is easy to measure with telescopes. Before the impact, Dimorphos circled Didymos every 11 hours and 55 minutes. The team would have counted a change of 73 seconds as success; the actual change was about 33 minutes, partly because the impact threw off a huge plume of rock and dust that pushed the asteroid further. A small Italian satellite, LICIACube, photographed the plume, and the European Space Agency's Hera probe, launched in 2024, is due to arrive in late 2026 to study the crater.

NASA DART missionRead card
WonderSpace

NASA's Parker Solar Probe, launched in 2018, flies through the Sun's outer atmosphere, the corona. In December 2024 it passed just 6.1 million kilometres from the solar surface, closer than any spacecraft before it.

The probe is named after the astrophysicist Eugene Parker, who in 1958 predicted the solar wind, the stream of charged particles flowing out from the Sun; it was the first NASA spacecraft named after a living person. A carbon-composite heat shield about 11 centimetres thick faces the Sun and heats to around 1,000 °C, while the instruments behind it stay near room temperature. Seven flybys of Venus shrank its orbit step by step. At its closest passes it travels at about 690,000 kilometres per hour, the fastest any human-made object has gone. In 2021 it became the first spacecraft to fly through the corona. Its measurements help explain how the solar wind is launched and how solar storms can disrupt satellites and power grids.

Parker Solar ProbeRead card
DriveBiography

Fazlur Rahman Khan, a Bangladeshi-American structural engineer, made very tall buildings cheaper to build with his 'tube' systems, in which a tower's outer walls work together to resist the wind. They shaped Chicago's John Hancock Center and the Sears Tower, now Willis Tower.

Before Khan, most skyscrapers relied on a rigid internal frame of steel columns and beams, and the taller they went, the more steel they needed to keep them from swaying in the wind. In Khan's framed tube, columns are set close together around the outside of the building and tied by deep beams called spandrels, so the whole outer wall acts like one stiff, hollow tube anchored in the ground. Working at the Chicago firm Skidmore, Owings & Merrill, he developed variations: the John Hancock Center (1969) braces its tube with giant diagonal X-shapes, and the Sears Tower (1973) bundles nine tubes together. Khan was born in Dhaka in 1929 and died in 1982.

Fazlur Rahman KhanRead card
Next card in the archiveIn 2014 Maryam Mirzakhani, an Iranian mathematician at Stanford University, became the first woman to win the Fields Medal, one of the highest honours in mathematics. She won it for work on the geometry of curved surfaces and on the space of all the shapes such surfaces can take.Read next →