Sid

SID is an acronym with multiple meanings in different fields, including computing, aviation, and electronics. It does not correspond to a single universal concept, and its meaning must be inferred from context.

In computing, SID most commonly refers to a Security Identifier. A Windows SID is a unique value assigned to a user account, group, or computer account. It is used by the operating system’s security subsystem to identify principals in authentication and authorization processes and to enforce access control lists. SIDs are created by the domain or local security authority, stored in security tokens, and embedded in permissions on files and other resources. They are persistent across user name changes and can be involved in migrations, where SID history may be retained to preserve access rights.

In aviation, SID stands for Standard Instrument Departure. A published routing used to transition from takeoff to en route airspace under instrument flight rules, detailing initial headings, altitudes, and waypoints. SIDs are designed to improve safety and efficiency, reduce conflicts, and manage traffic around busy airports, sometimes with variations for noise abatement or terrain.

In electronics and retro computing, SID denotes the Sound Interface Device, the sound chip used in the Commodore 64 family. The MOS Technology SID chip provides programmable oscillators, envelopes, and filters, contributing to distinctive timbres that are celebrated in chiptune music and vintage computing soundtracks.

Other uses occur in various contexts as an acronym for organizations, project identifiers, or general identifiers in software and data systems. Context generally clarifies the intended meaning of SID.