Glossary of embedded & SBC terms
Every term used across the Embedded & Single-Board Computers module, defined in plain language and linked to the lesson where it’s explained in full. Skim it as a refresher, or use your browser’s find (Ctrl/Cmd-F) to jump to a word. Terms are grouped by theme, roughly in the order the module introduces them.
Looking for deeper reference entries on hardware families, chips, and organizations? The Field Guide covers them alongside the RF and software worlds.
The landscape
Embedded system — A computer built into a device to do one dedicated job, unattended — the computers hidden in routers, cars, and appliances. See What is an embedded system?
Single-board computer (SBC) — A complete computer — processor, RAM, storage slot, USB, networking — on one small board running a real operating system; the Raspberry Pi is the canonical example. See SBC vs microcontroller vs PC
Microcontroller (MCU) — A single-chip computer with no operating system that runs one program with instant startup, precise timing, and tiny power draw — Arduino and ESP32 territory. See SBC vs microcontroller vs PC
Appliance — A computer dedicated to one job, expected to run unattended and recover on its own — the design goal of this module’s final build. See What is an embedded system?
Headroom — Spare capacity (CPU, RAM, power, thermal) left above a workload’s needs, so busy moments don’t push the system over a cliff. See Picking a board
System-on-chip (SoC) — One chip integrating CPU cores, GPU, memory controller, and I/O controllers — the reason an SBC fits on a credit card and can’t be upgraded. See ARM and the system-on-chip
ARM — The company (and architecture) whose licensed CPU core designs power nearly every phone and small board; optimised for performance per watt. See ARM and the system-on-chip
Instruction set — The vocabulary of operations a CPU understands; compiled software is built for one instruction set and won’t run on another. See ARM and the system-on-chip
arm64 / aarch64 — The 64-bit ARM architecture; the flavour to match when
downloading binaries for a modern Pi (uname -m tells you which you have). See
ARM and the system-on-chip
Ecosystem — The software, documentation, accessories, and community around a board — the Raspberry Pi’s real moat, and worth more than spec-sheet numbers for a first build. See Why the Raspberry Pi?
OS & setup
OS image — A byte-for-byte snapshot of a complete bootable disk, written directly onto an SD card; how operating systems are installed on SBCs. See Operating systems for small boards
Raspberry Pi OS — The first-party Debian-based Linux distribution for Raspberry Pi boards; the default foundation for Pi projects. See Operating systems for small boards
Lite image — An OS image with no graphical desktop — boots to a text console; the right choice for headless appliances. See Operating systems for small boards
Boot partition — The small FAT partition of an SBC’s card holding firmware, kernel, and plain-text config files — editable from any PC, which enables headless preconfiguration. See Operating systems for small boards
Flashing — Writing an OS image byte-for-byte onto a card or drive, replacing its entire contents with a bootable system. See Flashing an OS image
Headless — Running a computer with no monitor or keyboard, operated entirely over the network — the normal state of an SBC appliance. See First boot & SSH
SSH (Secure Shell) — The encrypted remote-login protocol that puts a board’s shell in your terminal; the way everything on a headless board gets done. See First boot & SSH
mDNS — Multicast DNS, which lets a board advertise itself as hostname.local so
you can find it without knowing its IP address. See
First boot & SSH
Buying decisions
A1 / A2 class — SD-card application-performance ratings measuring random read/write speed — the best predictor of how fast Linux feels on a card. See Storage & SD cards
High-endurance card — An SD card built with wear headroom for continuous recording — the right card class for an always-on appliance. See Storage & SD cards
NVMe — A fast, direct SSD interface some boards offer; with USB SSDs, the durable, quick upgrade over SD storage. See Storage & SD cards
Undervoltage — The board’s supply voltage sagging below spec — the classic cause of random crashes, USB resets, and SD corruption on SBCs. See Power supplies
Power budget — The sum of current the supply must deliver — board plus every bus-powered peripheral — with margin; exceeded budgets fail intermittently. See Power supplies
vcgencmd — The Raspberry Pi firmware query tool: measure_temp for temperature,
get_throttled for undervoltage and throttling flags. See
Power supplies
Passive cooling — Removing heat with heatsinks or a thermal metal case — silent, with no moving parts to fail; the appliance favourite. See Cases & cooling
Active cooling — Removing heat with a fan — more cooling per dollar, at the cost of noise, dust, and a wear item. See Cases & cooling
Load average — Linux’s measure of runnable work; sustained values at or above the core count mean saturation — the evidence-based upgrade signal. See When you need more than a Pi
Mini PC — A small, quiet x86 computer — the next rung when a project outgrows an SBC; same Linux, same skills, more of everything except GPIO. See When you need more than a Pi
Running like a server
sudo — Per-command administrative privilege for a normal user, logged each use — how root power is exercised without logging in as root. See Users, permissions & updates
unattended-upgrades — The Debian mechanism that installs security patches automatically — how an appliance stays patched during the months you forget it. See Users, permissions & updates
Service (daemon) — A long-running background program with no terminal, started and supervised by the init system. See Services with systemd
systemd — The init system on modern Linux: starts services at boot, restarts them
on failure, and collects their logs; driven with systemctl. See
Services with systemd
Unit file — The short INI-style file describing how systemd runs a program —
ExecStart, the service user, and restart policy. See
Services with systemd
journal / journalctl — systemd’s log store and its reader (journalctl -u name
-f follows a service live) — the window into a headless daemon. See
Services with systemd
DHCP reservation — A router setting that always hands a given board the same IP address — the low-maintenance way to make an appliance’s address permanent. See Networking your board
Talking to hardware
GPIO — General-purpose input/output: header pins your code drives high/low or reads — the SBC’s direct line to LEDs, buttons, and electronics. See GPIO basics
Logic level — The voltage a board’s pins speak (3.3 V on a Pi); feeding a pin more than its logic level damages it. See GPIO basics
Pull-up / pull-down — A resistor (often internal) giving an input pin a defined rest state, without which it floats and reads noise. See GPIO basics
Bus-powered — A USB device drawing all its power through the port — every milliamp comes out of the board’s own supply budget. See USB & powered hubs
Powered hub — A USB hub with its own supply, so downstream devices stop drawing through the board — the cure for crowded-bus resets. See USB & powered hubs
UART (serial) — The two-wire point-to-point bus (TX/RX at an agreed baud rate) — consoles, GPS modules, and the headless board’s debugging lifeline. See Serial, I2C & SPI
I2C — The shared two-wire bus (SDA/SCL) where many slow devices coexist, each at
its own address — the sensor bus, probed with i2cdetect. See
Serial, I2C & SPI
SPI — The fast four-wire bus (MOSI/MISO/SCLK plus a chip-select per device) for displays, converters, and flash. See Serial, I2C & SPI
HAT — Hardware Attached on Top: a standardised add-on board that presses onto the full header and identifies itself via an onboard EEPROM. See HATs & add-ons
PoE (Power over Ethernet) — Powering a board through its network cable via a PoE HAT and switch — one-cable installs for closet and attic appliances. See HATs & add-ons
RTL-SDR — The ~$30 USB software-defined-radio dongle that streams a slice of raw spectrum to software — the appliance’s radio front end. See Connecting an SDR
Module blacklist — Telling the kernel not to load a driver — required so the DVB-T TV-tuner module doesn’t claim the RTL-SDR before SDR software can. See Connecting an SDR
rtl_test — The acceptance test for a dongle: stream samples and report losses; a clean run separates hardware problems from software ones forever after. See Connecting an SDR
Running 24/7
Thermal throttling — The SoC reducing its own clock speed as it nears its temperature limit — silent, protective, and a real-time decoder’s enemy. See Thermal throttling
Write cycles / wear — Flash cells endure a finite number of writes; constant small writes (logs above all) wear cheap cards to death. See SD-card wear
Wear-levelling — A flash controller spreading writes across all cells so no block dies early — done well in SSDs, barely in cheap cards. See SD-card wear
Write amplification — Small writes costing full flash-block erase cycles — why a trickle of log lines wears more than its byte count suggests. See SD-card wear
tmpfs — A RAM-backed filesystem: contents vanish at reboot, wear cost zero — where scratch data and (via log2ram) buffered logs belong. See SD-card wear
Retention policy — The rule bounding stored data (recordings pruned after N days) so growth is flat instead of a countdown to a full disk. See SD-card wear
Hardware watchdog — A silicon countdown timer that reboots the board unless the OS keeps resetting it — the escape from a hung kernel that software can’t provide. See Watchdogs & recovery
Health check — A scheduled probe of observable work (console answers, recordings land) that restarts or alerts when the answer is no. See Watchdogs & recovery
Power-cycle test — The design test for appliances: pull power, restore it, and everything must resume unattended. See Watchdogs & recovery
SSH keys — A cryptographic key pair replacing password login — stronger, unphishable, and the standard for administering remote boards. See Remote administration
tmux — A terminal multiplexer keeping remote work alive when the connection drops — where every long or risky remote command belongs. See Remote administration
Golden image — A full byte-for-byte backup of the working card, taken at milestones — the ten-minute path back from any disaster. See Backups & images
rsync — The sync tool that copies changed files efficiently over SSH — how configs and data flow off the board on a schedule. See Backups & images
Vitals — The four numbers worth watching on any board: temperature, load, disk, and service state — plus whether the work itself is happening. See Monitoring your board
Alert fatigue — The failure mode where alerts fire so often you ignore them; the reason to alert only on actionable states. See Monitoring your board
The GopherTrunk appliance
ARM build — A binary compiled for the ARM architecture; GopherTrunk ships ARM
Linux builds, matched to the OS via uname -m. See
Install GopherTrunk on a Pi
Web console — GopherTrunk’s browser interface, served over the network — the reason the appliance itself never needs a display. See Install GopherTrunk on a Pi
Real-time load — Work with a hard deadline: samples arrive continuously, and falling behind means dropped samples, not lateness. See Tuning for small CPUs
Dropped samples — Radio samples lost because power, USB, or CPU failed to keep the stream flowing — the common currency of SBC-SDR failure modes. See USB SDR gotchas
Self-interference — The board’s own RF emissions (SoC clocks, supplies, cheap cables) raising the noise floor of the SDR beside it — fixed with antenna distance and shielded cables. See USB SDR gotchas
Port-forward — A router rule exposing an internal service to the internet — the convenient click an appliance’s console must never receive. See Appliance networking & access
VPN — An encrypted, authenticated tunnel that puts your remote device virtually on your home LAN — the right way to reach the console from anywhere. See Appliance networking & access
SSH tunnel — Carrying a service’s port through an SSH connection — on-demand remote access with zero new infrastructure. See Appliance networking & access
Acceptance test — The pass/fail check ending each build phase, proving its layer before the next is stacked — the method that localizes every failure. See A complete appliance build