Technology and the built world

Directory (computing)

A directory, also called a folder, is a file system container holding named references to files and other directories, organized as a hierarchy called a directory tree.

Directory-based coherence is a cache coherence scheme for shared-memory multiprocessors in which a directory tracks which caches hold each memory block, letting writes go only to those caches instead of being broadcast, as in snooping systems.

DirecTV

DirecTV is an American direct-broadcast satellite and streaming television service launched in 1994, once the country's top pay-TV distributor and now wholly owned by TPG.

DirectX

DirectX, also known as Microsoft DirectX, is a collection of Microsoft APIs for audio and video hardware, first released in 1995 and best known for its Direct3D graphics APIs.

DirectX Raytracing

DirectX Raytracing (DXR) is a Microsoft ray tracing API introduced as a feature of DirectX 12, announced in 2018 and shipped with the Windows 10 October 2018 Update.

Direktorat Jenderal Perhubungan Darat

Direktorat Jenderal Perhubungan Darat, or Ditjen Hubdat, is Indonesia's Directorate General of Land Transportation, the Ministry of Transportation unit that formulates and executes national land transport policy.

Dirk

A dirk is a long dagger, originally the heavy thrusting knife carried by the Highlanders of Scotland and later the straight-bladed sidearm worn by naval officers in the 18th and 19th centuries.

Sep 20, 2026

Dirk Englund

Dirk Englund is a professor of electrical engineering and computer science at MIT who leads the Quantum Photonics Laboratory, researching quantum communication, computing, sensing, and photonic AI hardware.

Dirt Devil

Dirt Devil is an American budget vacuum cleaner brand owned by TTI Floor Care North America, best known for its low-priced handheld vacuums, above all the 1984 Hand Vac.

Dirty bomb

A dirty bomb, or radiological dispersal device, combines conventional explosives with radioactive material to scatter contamination; no atomic blast occurs, and none has been used in terrorism.

Dirty paper coding

Dirty paper coding is a channel coding technique that pre-codes transmitted data so a receiver decodes reliably despite known interference, with no power increase or rate loss.

Disaggregated memory

Disaggregated memory is a datacenter architecture that decouples main memory from compute nodes into shared, independently scalable pools over an interconnect, raising memory utilization across a datacenter.

Disc cutter

A disc cutter is a rolling cutting tool mounted on a tunnel boring machine cutterhead, whose hardened steel ring crushes rock into chips under high pressure.

Disc rot

Disc rot: deterioration of optical discs (CDs, DVDs, LaserDiscs, Blu-ray) from dye degradation, aluminum oxidation, label ink, or storage conditions, making discs unreadable; studied by NIST/LoC and CCI.

Disc wheel

A disc wheel is an aerodynamic spokeless bicycle wheel, used mainly as a rear wheel in time trials and track racing since Francesco Moser's 1984 hour record.

Disciplined Agile

Disciplined Agile is a process-decision toolkit owned by the Project Management Institute, co-created by Scott Ambler and Mark Lines, that lets teams choose their own way of working.

DisCoCat

DisCoCat, short for categorical compositional distributional semantics, is a mathematical model of meaning that combines word vectors with grammatical structure, introduced by Coecke, Sadrzadeh, and Clark in 2010.

Discogs

Discogs, short for discographies, is a user-built online database of music releases and a marketplace for buying and selling vinyl, CDs, and cassettes, founded in 2000.

Discontinuous deformation analysis

Discontinuous deformation analysis (DDA) is a numerical method that simulates the motion and deformation of discrete blocks in jointed rock masses, applied mainly to rockfall, rock slopes, and landslides.

Discontinuous PWM

Discontinuous PWM, also called bus-clamping PWM, is a pulse-width modulation strategy for three-phase voltage-source inverters in which each leg periodically stops switching to cut switching losses.

Discord

Discord is a communication platform combining group text chat, voice calls, and video, launched in May 2015 for gamers and reported by 2025 to have over 200 million monthly users.

Discounted cumulative gain

Discounted cumulative gain (DCG) is a ranking evaluation metric that discounts graded relevance by rank position, introduced by Järvelin and Kekäläinen in 2002 and widely used in information retrieval.

Discoverer

Discoverer was the public cover name of a US satellite series launched from Vandenberg between 1959 and 1962, masking the classified CORONA film-return spy satellite program.

Discrete cosine transform

The discrete cosine transform (DCT), also called cosine transform, is a family of real-valued Fourier-related transforms, introduced in 1974, that underlies JPEG image and MP3 audio compression.

Discrete elastic rods

Discrete elastic rods (DER) is a numerical method, introduced at SIGGRAPH in 2008, for simulating slender elastic bodies such as hair strands, cables, and soft robot limbs.

Discrete element method

The discrete element method (DEM), also called the discrete element model, is a numerical simulation technique that computes the motion of large particle assemblies contact by contact.

Discrete event simulation

Discrete event simulation is a modeling method where a system's state changes only at discrete event times, used to estimate waiting times, throughput, and bottlenecks.

Discrete phase model

The discrete phase model (DPM) is an Euler–Lagrange method in computational fluid dynamics that tracks particles, droplets, or bubbles through a continuous carrier fluid in dilute flows.

Discrete sine transform

The discrete sine transform (DST) is a family of invertible linear transforms expressing a sequence as a sum of sines, the odd-symmetry counterpart of the discrete cosine transform.