SPIs

SPIs is an acronym used for several concepts across different fields. This article summarizes the major meanings and how they are used in practice.

In electronics, SPI refers to Serial Peripheral Interface, a synchronous serial communication protocol. It uses a master-slave arrangement with four signals: clock (SCK), master output/slave input (MOSI), master input/slave output (MISO), and a chip-select line (SS) for each device. SPI supports full-duplex transfer and can connect multiple peripherals, typically at higher data rates than I2C, though it requires more wiring and device-specific configuration. Common applications include sensors, flash memory, displays, and memory cards.

In biology, SPIs commonly denotes serine protease inhibitors, a broad class of proteins that inhibit serine proteases such as trypsin and chymotrypsin. They include serpins and non-serpin inhibitors and regulate processes such as digestion, coagulation, immune defense, and parasite-host interactions. Dysfunction or imbalance of SPIs is associated with disease; some SPIs serve as therapeutic targets or drugs.

In climate and hydrology, SPI stands for Standardized Precipitation Index, a statistical measure of precipitation anomalies used to detect drought and wet periods. SPI is calculated for multiple timescales (for example, 1, 3, 6, and 12 months) to assess short- and long-term moisture conditions and supports drought monitoring and water resource planning.

In software engineering, SPI can also mean Service Provider Interface, a design pattern that allows a framework to be extended by pluggable implementations. An SPI defines interfaces that service providers implement, enabling dynamic discovery and loading at runtime. This usage complements but is distinct from application programming interfaces (APIs) used by end-user developers.