macOS applications evolved from Classic Mac OS's resource fork structure to the modern bundle architecture inherited from NeXTSTEP. Today's .app bundles contain a standardized directory hierarchy with executable code in MacOS, resources like icons and GUI components, frameworks, and metadata in Info.plist. Modern additions include code signatures in _CodeSignature, App Store receipts, notarization tickets, and self-contained components like XPCServices, plugins, and extensions that were previously installed separately. This centralization improves installation, updates, removal, and security by keeping all components within the app's signature protection.
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