All articles starting with S

System software

System software is the layer of programs that manages a computer's hardware resources and provides foundational services for application software, including operating systems, device drivers, and middleware.

System strength (electric power)

System strength is a property of an AC power system describing how well the voltage waveform resists disturbances. It is measured by available fault current, often via the short-circuit ratio.

System T

System T, also called Gödel's T, is a quantifier-free theory of functionals of finite type introduced by Kurt Gödel in 1958 as the target of his Dialectica interpretation.

System time

System time is the current date and time an operating system maintains and exposes to its processes, based on UTC and usually kept accurate by NTP.

System Usability Scale

The System Usability Scale (SUS) is a ten-item questionnaire giving a 0 to 100 score of perceived usability; the most widely used such scale, it averages 68 across 500 evaluations.

System Wide Information Management

System Wide Information Management (SWIM) is an air traffic management concept, defined by ICAO, for exchanging aviation information between qualified parties through shared, interoperable services.

System X (telephony)

System X is a family of stored-program digital telephone exchanges developed in the UK by the Post Office with GEC, Plessey, and STC, deployed from 1981.

System-theoretic process analysis

System-theoretic process analysis (STPA) is a hazard analysis method, based on Nancy Leveson's STAMP, that models systems as feedback control loops to find unsafe control actions and loss scenarios.

Systema Naturae

Systema Naturae is Carl Linnaeus's classification of minerals, plants, and animals, first published in Leiden in 1735 as an 11-page folio; its 10th edition (1758) starts zoological nomenclature and named Homo sapiens.

Systemantics

Systemantics, also known as The Systems Bible, is a 1975 satirical book by physician John Gall on how systems behave and fail, best known for Gall's Law.

Systematic Biology

Systematic Biology (formerly Systematic Zoology) is the bimonthly peer-reviewed journal of the Society of Systematic Biologists, published by Oxford University Press since 1952, covering systematics, phylogenetics, and evolution; 2025 impact factor 6.2.

Systematic desensitization

Systematic desensitization, or graduated exposure therapy, is a behavioral therapy for phobias in which a relaxed client is gradually exposed to feared situations, from least to most disturbing.

Systematic evidence map

A systematic evidence map is an evidence synthesis that catalogs what research exists on a broad topic, often in a visual matrix or database, to identify knowledge gaps.

Systematic evolution of ligands by exponential enrichment

Systematic evolution of ligands by exponential enrichment (SELEX) is an in vitro selection method, reported in 1990, that iteratively enriches oligonucleotide pools to isolate aptamers binding a target molecule.

Systematic layout planning

Systematic layout planning (SLP) is a step-by-step method for arranging facilities, developed by Richard Muther and first published in 1961 and applied to factories, warehouses, offices, and hospitals.

Systematic mapping

Systematic mapping, also called systematic map or mapping review, is an evidence synthesis method that charts a field's literature to reveal evidence clusters and gaps.

Systematic measurement error

Systematic measurement error, or systematic error, is the component of measurement error that stays constant or varies predictably in replicate measurements, with its estimate called measurement bias.

Systematic placement and evolution of whisk ferns

Whisk ferns (Psilotaceae) are a small family of rootless, leafless vascular plants, once classed as relics of early land plants, that molecular studies place as ferns sister to Ophioglossaceae.

Systematic prostate biopsy

Systematic prostate biopsy is a diagnostic procedure that samples the prostate with a needle at fixed, standardized locations, usually under ultrasound guidance, to detect cancer.

Systematic review

A systematic review, also called a systematic literature review, is a research synthesis answering a pre-specified question, with study eligibility criteria fixed in advance, unlike a narrative review.

Oct 10, 2026

Systematic risk

Systematic risk is the component of an investment's risk driven by economy-wide forces such as interest rates, inflation, and recessions, and it cannot be removed by diversification.

Systematic sampling

Systematic sampling is a probability sampling design in which units are selected at a fixed interval through an ordered list after one random starting point.

Systematic theology

Systematic theology, also called systematic divinity, is the branch of theology that sets out a religious tradition's teaching as an ordered whole, testing doctrines for consistency.

Systematics

Systematics is the biological science of organismal diversity and phylogeny, spanning taxonomy, cladistics (Hennig, 1966), species delimitation, and molecular phylogenetics; distinct from phenetics and from taxonomy alone.

Systematics and fossil record of Dryopteridaceae

Dryopteridaceae, the shield-fern family, the largest fern family with over 2100 species; systematics revised in 2025 into seven subfamilies and 24 genera including Pseudarachniodes, with a sparse fossil record from Cretaceous amber and permineralized rhizomes.

Systematics of Blastocladiomycota

Blastocladiomycota, synonym Allomycota, a phylum of zoosporic fungi elevated from order Blastocladiales by James et al. 2006; one order, five families, saprobes, and parasites; deep placement still unresolved.

Systematics of irregular echinoids

Systematics of irregular echinoids covers the classification of Irregularia, sea urchins whose anus migrated posteriorly, giving bilateral symmetry and burrowing habits, including heart urchins, sand dollars, and sea biscuits.

Systematics of Lactarius

Systematics of Lactarius: classification and phylogeny of the milkcap genus Lactarius (Russulales), split molecularly into Lactarius s. str., Lactifluus, and Multifurca, with three subgenera, ITS-based species delimitation, and regional revisions in Korea, Africa, and North America.

Systematics of Pteridaceae

Systematics of Pteridaceae: classification of the maidenhair and brake fern family, over 1,000 species in five subfamilies, molecular phylogeny, cheilanthoid taxonomy, and recent PPG II reclassification.