SID
A security identifier (SID) is a unique, immutable alphanumeric string generated by Microsoft Windows to reference security principals such as user accounts, groups, or computer objects within its operating system and Active Directory environments.[1][2] SIDs form the core of Windows' discretionary access control mechanism, enabling precise authorization decisions by uniquely identifying entities regardless of name changes or domain migrations, with a structure comprising a header (including revision and identifier authority values) followed by variable subauthority components that ensure global uniqueness.[3][4] Introduced in Windows NT and persisting across subsequent versions, SIDs underpin features like access control lists (ACLs), auditing, and impersonation, preventing unauthorized access while supporting scalability in enterprise networks; well-known SIDs, such as those for "Everyone" (S-1-1-0) or "Administrators" (S-1-5-32-544), provide standardized references for common principals without relying on domain-specific resolution.[5][6] Their design prioritizes security over readability, as SIDs like S-1-5-21-3623811015-3361044348-30300820-1013 remain opaque yet reliable for policy enforcement, though mismanagement in multi-domain setups can lead to access issues resolvable via tools like PsGetSid or domain trusts.[7][8]Technology and computing
Sound Interface Device
The Sound Interface Device (SID), designated MOS Technology 6581, is a programmable sound generator chip designed for analog synthesis, primarily integrated into Commodore computers such as the Commodore 64 released in August 1982.[9] Developed by engineer Bob Yannes at MOS Technology in 1981, the SID combines digital control logic with analog circuitry to produce audio signals, enabling complex sound generation beyond simple tones typical of contemporary microcomputers.[10] Its architecture supports three independent oscillator circuits (voices), each configurable for triangle, sawtooth, pulse-width modulated square, or pseudo-random noise waveforms, with simultaneous multichannel output at a sampling rate derived from the system's 1.023 MHz clock (NTSC variant).[9] [11] Each SID voice incorporates a 12-bit frequency register for pitch control spanning approximately five octaves, an amplitude modulation circuit, and a dedicated ADSR (attack, decay, sustain, release) envelope generator that shapes volume over time via programmable 8-bit parameters for attack (up to 40 ms), decay/sustain/release (up to 6.4 seconds combined).[11] The chip includes a master analog low-pass filter with configurable resonance (0-15 levels) and cutoff frequency (up to 12 kHz), switchable to band-pass or high-pass modes, alongside a volume control register for overall output amplitude.[9] [11] Audio output is monaural, filtered through an external RC network, and the SID supports synchronization between voices for ring modulation effects, contributing to its characteristic "dirty" analog timbre from NMOS fabrication imperfections like oscillator leakage.[10] Programming the SID occurs via memory-mapped I/O in the Commodore 64's address space (D400 to D41F for core registers), using 29 8-bit registers: 24 write-only for synthesis parameters and five read-only for monitoring oscillator output and status (e.g., envelope levels, 4-bit ADC for external input).[11] Software control, often in 6502 assembly for real-time precision, allows dynamic waveform modulation, filter sweeps, and effects like the "digi-noise" technique exploiting early 6581 revisions' digital audio artifacts for sampled playback, though limited to low fidelity (4-bit, ~4 kHz).[10] The chip lacks built-in digital-to-analog conversion for samples, relying on analog techniques, which influenced chiptune composition by favoring subtractive synthesis over additive methods.[12] Two primary revisions exist: the original 6581 (NMOS logic, produced 1982-1986) with higher distortion and a "zero-frequency resonance bug" causing audible clicks at low pitches, and the 8580 (HMOS, introduced 1987) with improved filter stability, reduced noise floor, and enhanced high-frequency response but lacking the 6581's distinctive distortion harmonics sought by musicians.[13] A rare 6582 variant mirrors the 8580 die for consumer applications.[14] These differences necessitate chip identification (via markings or test tones) for accurate emulation in modern reproductions, as the 8580's cleaner sound alters classic compositions' timbre.[10] The SID's design prioritized musical expressiveness over efficiency, enabling the Commodore 64's enduring legacy in demoscene and game audio despite computational constraints.[9]Security Identifier
A security identifier (SID) is a unique, variable-length value used in Microsoft Windows NT-based operating systems to identify security principals, such as user accounts, groups, or other trustees that can be authenticated by the system.[15] Each SID is generated and issued by a local or domain security authority, ensuring uniqueness within its scope, and remains immutable even if the associated account name changes.[15] SIDs form the basis for access control decisions, as the operating system compares SIDs directly rather than relying on potentially alterable names or friendly identifiers.[1] The structure of a SID follows a hierarchical binary format defined in the Windows API, consisting of a one-byte revision level (typically 1 for current implementations), a six-byte identifier authority value (which specifies the issuing authority, such as the NT Authority for local accounts), a variable number of 32-bit subauthority values (up to 15, indicating relative identifiers within the domain or machine), and an optional subauthority count.[3] In textual representation, SIDs appear as strings in the formS-R-I-S-SA..., where S denotes the SID prefix, R is the revision level, I is the identifier authority in hexadecimal, and subsequent S values are decimal subauthorities; for example, the SID for the local Administrators group on a standalone system is S-1-5-32-544.[16] Domain-issued SIDs incorporate a domain identifier as the first subauthority, followed by a relative ID (RID) unique to the principal within that domain, such as S-1-5-21-domain-1001 for a user with RID 1001.[1]
SIDs are integral to Windows access control lists (ACLs) and security descriptors attached to securable objects like files, registry keys, processes, and network resources.[1] When evaluating access requests, the system maps the requesting principal's SID to permissions defined in the object's discretionary ACL (DACL), granting or denying operations based on SID matches rather than usernames to maintain security integrity across renames or migrations.[15] Well-known SIDs, predefined by Microsoft for generic entities, simplify this process; examples include S-1-1-0 for the "Everyone" group (encompassing all users) and S-1-5-32-544 for the built-in Administrators group, which are consistent across all Windows installations regardless of local configuration.[5]
In Active Directory environments, domain SIDs ensure cross-machine consistency, with child domains inheriting parent identifiers while appending unique RIDs.[1] Tools like the Windows Security Identifier API (e.g., ConvertSidToStringSid) allow programmatic manipulation, but direct SID alteration is restricted to prevent privilege escalation risks.[3] Historical issues, such as SID history in migrations, have enabled attacks like SID history injection, underscoring the importance of auditing SID usage in enterprise security.[17]