Other platforms

NTFS attaches a security descriptor with an ordered list of ACEs to every file, so any number of users and groups can each be allowed or denied specific rights. Unix mode bits offer only three fixed slots of read/write/execute.

A Windows HANDLE is an opaque, per-process entry in that process's handle table referring to an object created by the NT object manager — a file, event, mutex, process, thread or registry key. A Unix file descriptor is a small integer naming a much narrower set of objects.

The Windows registry is the OS's hierarchical configuration database. HKLM holds machine-wide settings backed by hive files in %SystemRoot%\System32\config; HKCU holds the currently logged-on user's settings, backed by NTUSER.DAT inside that user's profile folder.

Windows NT layers user mode — applications, subsystem DLLs such as kernel32.dll, and ntdll.dll — over kernel mode, where ntoskrnl.exe holds the executive managers (I/O, memory, process, security), the kernel layer that schedules and dispatches interrupts, plus drivers and the HAL.

PowerShell's execution policy is refusing to load the script file — Windows clients default to Restricted, servers to RemoteSigned. It guards against accidentally running an untrusted file, not against a determined user: anyone who can start PowerShell can bypass it.

A Launch Daemon runs in the system domain from boot, normally as root, with no login session and no access to a user's screen. A Launch Agent runs inside a logged-in user's session, as that user, and can reach the GUI.

The browser tags its download with the com.apple.quarantine extended attribute; curl does not. Gatekeeper only evaluates quarantined files, so the tagged copy is checked for a valid signature and notarization on first launch while the untagged copy simply runs.

An APFS container owns all the blocks of its partition, and every volume inside it allocates from that one shared free pool. Volumes therefore have no fixed size, and each reports the container's remaining space as its own available space.

Homebrew uses a separate /opt/homebrew prefix on Apple Silicon so an arm64 installation can coexist with an Intel one under /usr/local and so bottles are built for a known default prefix. That directory is not on the default PATH, so brew shellenv must add it.

XNU combines a Mach core providing tasks, threads, port-based IPC and virtual memory with a BSD layer providing POSIX syscalls, processes, VFS and the network stack, plus IOKit for drivers. All of it runs in one kernel address space, so it is hybrid in structure but monolithic in performance.

Raspberry Pi GPIO pins run 3.3 V logic and are not 5 V tolerant, so 5 V on an input can damage the pin or the SoC. Put a level shifter or a resistor divider in between.

Consumer microSD cards have limited write endurance and simple controllers, so constant small writes from logs, databases and swap wear them out, while power loss mid-write can corrupt the card's internal mapping. Cut the write rate, or move the root filesystem off the card entirely.

Read the firmware's throttle flags with vcgencmd get_throttled and check the kernel log for under-voltage messages. The bitmask separates a current problem from one that has occurred since boot, and distinguishes low voltage from thermal throttling.

Linux now exposes GPIO as character devices at /dev/gpiochipN, and a program requests specific lines through ioctls, usually via libgpiod. The kernel releases a line when the requesting file descriptor closes. The older /sys/class/gpio export interface is deprecated and leaves lines stranded.

Argue against it when the environment, timing or reliability requirements exceed a consumer board: wide ambient temperature range, hard real-time deadlines, uncorrected memory errors, or a mechanical socket that must survive vibration. Move to a Compute Module with eMMC, an industrial SBC, or a microcontroller.