How macOS actually works
Every term in these articles, defined once, plainly.
APFS — the modern Mac filesystem. Containers share space, files clone cheaply, snapshots freeze states.
Volume — a mountable filesystem. One drive can hold several; each has its own search index.
Package / bundle — a folder shown as one item (.app, .photoslibrary). Search indexes it as a single object, not its contents.
inode / file ID — the filesystem's identity for a file, stable across renames within a volume.
Firmlink — the APFS join stitching the read-only System volume and your Data volume into one apparent tree.
Index — a prepared copy of what you will search, so lookups skip the disk.
Spotlight — macOS's built-in content-and-metadata index and search.
mdfind / mdls / mdimport / mdutil — the Terminal tools for querying, inspecting, importing and managing the Spotlight index.
FSEvents — the macOS API reporting filesystem changes, letting an index stay current without rescanning.
Content search vs filename search — searching inside files (expensive, what Spotlight excels at) versus matching names (cheap, what a filename index excels at).
SIP (System Integrity Protection) — kernel-level immutability for system files; root cannot override it.
TCC / Full Disk Access — the privacy layer gating access to personal data like Mail and Messages until an app is granted permission.
Quarantine — the attribute on downloaded files triggering Gatekeeper's first-open check.
Sandbox — the confinement every Mac App Store app runs under, unable to read your filesystem freely.
Extended attributes (xattr) — hidden key-value data on files: tags, download origins, quarantine flags.
UTI (Uniform Type Identifier) — the file's real type, independent of its extension. Finder's Kind filter uses it.
Metadata — data about a file (size, dates, type, tags) as distinct from its contents.
Content search matches text inside files — expensive, Spotlight's strength. Filename search matches names — cheap, and what a dedicated index does instantly.
Transparency, Consent and Control — the privacy system behind Full Disk Access and the permission prompts.
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