Glossary

156 terms from Computer Hardware Basics, in plain words, each with the chapter that teaches it.

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A

ACPI: The standard that lets the operating system control power: sleep, the power button and fan speeds. It appears as acpi in /sys/firmware.
APFS: The file system used by Macs and iPhones. It is built for SSDs, and Windows can't read it without extra tools.
ARM: The instruction set used by phones, Apple silicon Macs and Snapdragon X Windows laptops. It usually uses less power than x86-64 for the same work, so batteries last longer.
ASCII: The agreed code that gives every letter a number; capital K is 75, or hex 4b. It is now part of the bigger Unicode code.
ATX: The standard full-size desktop motherboard. Micro-ATX is shorter and mini-ITX is small and square, and a case lists which of these sizes fit inside it.
awk: A small tool that picks lines and fields out of text. In awk -F, 'NR > 1 && $3 < 16' office.csv, -F, splits fields at commas, $3 is the third field and NR is the line number.

B

backup: A separate copy of files, kept somewhere else. RAID is not a backup, because a deletion is copied to every drive at once.
beep codes: Patterns of beeps or lights that report a failed POST before any picture appears. On many boards, one long beep and two short ones mean 'no graphics found', and the board's manual lists the rest.
binary: Numbers written with only 0 and 1. Each place is worth twice the place to its right (1, 2, 4, 8 …), so binary 11001000 is 200.
BIOS: The old PC firmware, used from 1981 until about 2010. It could only boot from MBR drives and has been replaced by UEFI, though many PCs still call their firmware settings 'BIOS'.
bit: The smallest piece of data: one switch that is off (0) or on (1).
BitLocker: Windows' disk encryption. It keeps its key in the TPM, which releases the key only if the boot chain is unchanged, so a stolen drive moved to another PC shows only scrambled bytes.
blocks: The fixed-size pieces, often 4 KiB, that a file system stores data in. mkfs.ext4 split Alex's 722 MiB partition into 184,832 blocks.
boost: The fastest clock speed a core reaches for short bursts while it's cool enough, as in 'up to 4.8 GHz'.
boot order: The firmware's list of drives to try booting from, such as 'USB stick, then SSD'. In the shipping PC, the SSD was missing from this list because its cable was loose.
booting: Starting a computer in a chain of stages: firmware and POST, then the bootloader, then the kernel, then services and the login screen. Each stage loads the next.
bootloader: The program the firmware starts, which loads the OS kernel into RAM. Examples are GRUB on Linux and Windows Boot Manager on Windows.
bottleneck: The slowest part of a machine, which holds the others back, so upgrading any other part won't help. In the shipping PC it was the hard drive, sitting at 100% busy.
buses: The copper paths on a motherboard that carry data between the parts. PCIe is the fast one.
byte: Eight bits, giving 256 patterns. That's enough for one letter or one number from 0 to 255, and it is always written as two hex digits.

C

cache: Small, very fast memory on the CPU chip that keeps copies of recently used data. It saves slow trips to RAM.
chipset: The helper chip on the motherboard that links slower devices (USB, SATA, network, sound) to the CPU through one shared connection. Its model name, such as B850 or Z890, tells you how many ports and slots a board can have.
clock speed: How many ticks per second the CPU's internal clock makes, in GHz; the clock keeps every step in time. It only compares chips of the same family and generation.
CMOS battery: The small coin battery on the motherboard. When it goes flat, the clock is wrong and the firmware settings are forgotten at each start.
comment: A note for the reader in a command or code line, started with `#`, that the computer ignores. Comments explain what a command does, so you can leave them out when you type it.
core: A complete processor inside a CPU chip, running its own fetch-decode-execute cycle. A chip with eight cores can run eight programs at the same moment.
CPU: The central processing unit, or processor. It runs the instructions of programs, but it can only work on what is in RAM.
CSM: A 'legacy' firmware setting that makes UEFI act like the old BIOS. Windows 11 needs UEFI, so leave it off.
CSV: Comma-separated values: one record per line, with its fields separated by commas and a first line of column names. office.csv holds one Kettle & Crane machine per line.

D

DDR: The family of RAM generations (double data rate), such as DDR4 and DDR5. Each generation is faster and has its notch in a different place, so modules only fit a board of the same generation.
Device Manager: The Windows tool that lists the hardware devices, grouped by kind. A yellow triangle there means a device's driver is missing.
digital signature: A proof, attached to a program, of who made it and that nobody has changed it since. Secure Boot checks it before starting a bootloader.
DIMMs: The long RAM modules used in desktop PCs.
disk encryption: Scrambling a whole drive so that only someone with the key can read it. Windows uses BitLocker, Macs use FileVault and Linux uses LUKS.
Disk Management: The Windows tool for partitioning and formatting drives, for example with New Simple Volume. On a Mac, Disk Utility does the same job.
DisplayPort: A display connection for PC monitors. Version 2.1 carries up to 80 Gb/s and can chain several monitors from one port.
DisplayPort Alt Mode: A DisplayPort picture signal carried over a USB-C port. Not every USB-C port has it, which is why a monitor can say 'No signal'.
dmesg: Prints the kernel log: a message for each piece of hardware the kernel finds and each hardware error it meets. It needs sudo.
dmidecode: Reads the firmware's table of parts. On a real PC, dmidecode -t memory shows each RAM slot's name, size, type and speed: what you need to buy a matching module. A VM doesn't have this table.
driver: A small program that translates between the OS and one kind of device. Devices in a standard class use drivers the OS already has; others, such as graphics cards and printers, need the maker's driver, which you should get only from OS updates or the maker's site.

E

EFI System Partition: The small FAT32 partition that holds the bootloader files on a UEFI machine. It uses FAT32 because that is simple enough for firmware to read.
escalate: To pass a problem to someone with more knowledge, tools or access, such as the maker's support or a repair shop, with your notes.
Ethernet: Wired networking with a cable that ends in a square-ish RJ45 plug, usually at 1 or 2.5 Gb/s. It is faster and steadier than Wi-Fi for desks that never move.
exFAT: A file system for USB sticks and SD cards that Windows, macOS and Linux can all read and write. It has no 4 GiB file limit.
expansion slots: Slots on the motherboard where extra cards, such as a graphics card or network card, plug in. In today's PCs they are PCIe slots, named by their lanes (x1, x4, x16).
ext4: The usual Linux file system. Alex formatted the practice drive's data partition with it.

F

FAT32: An old, simple file system that is readable everywhere and used for EFI partitions. Files on it can't be bigger than 4 GiB.
fetch-decode-execute cycle: The loop a CPU core runs for every instruction: read it from memory, work out what it means, then do it.
file system: The way a partition is organized into folders and files. It records each file's name, size, owner, dates and where its data sits.
firmware: The small program stored in a chip on the motherboard that runs first at power-on, does POST and starts the bootloader. You open its settings with a key such as F2 or Del, and it gets updates that must never be interrupted.
formatting: Creating an empty file system on a partition, for example with mkfs.ext4 or mkfs.vfat. It makes the old files unreachable, so check twice which drive you're formatting.
free: Shows the machine's RAM; -h prints sizes people can read. The total column on the Mem line is the RAM size.
function: A named block of commands in a script that you run by name, like a small command of your own. inventory.sh's flag function prints a problem and counts it.

G

GHz: Gigahertz: billions of ticks per second, so 3 GHz is three billion. It measures CPU clock speed.
GPT: The modern partition table (GUID partition table): up to 128 partitions, practically no size limit, and a backup copy at the end of the drive. UEFI needs it to boot.
GPU: The graphics processing unit: a processor built for drawing pictures by coloring millions of pixels at once.
graphics card: A plug-in card with its own GPU and memory. It sits in the x16 PCIe slot, needs power cables from the PSU, and the monitor plugs into it rather than the motherboard.

H

hard disk drive (HDD): Storage that keeps bits as magnetic spots on spinning platters, read by a head on a moving arm. It is cheap per terabyte but slow at jumping between small files.
hardware: The physical parts of a computer: the things you can touch.
HDMI: The display connection used by TVs and most monitors. HDMI 2.0 has about 14 Gb/s usable, enough for 4K at 60 Hz, and HDMI 2.1 carries 48 Gb/s.
heatsink: A block of metal fins on a chip that carries its heat away, helped by a fan. Dust packed in its fins made Priya's PC overheat.
hexadecimal (hex): Base 16, written with the digits 0 to 9 and a to f; one hex digit stands for 4 bits, so a byte is two hex digits (f5 is 245). A 0x in front, as in 0x80070070, only says 'this number is hex'.
Hyper-Threading: Intel's name for running two threads on one core; AMD calls it SMT. The second thread uses parts of the core the first leaves idle, but it isn't as fast as a second core.

I

I/O error: A failed read or write reported in the kernel log. Many of them naming a drive mean it is failing, so copy the data off at once.
if: A script statement that runs commands only when a test in square brackets is true. else gives the other case, and fi ends it.
inkjet printer: A printer that sprays tiny drops of liquid ink. It's good for photos and color, but ink costs more per page.
inodes: The records that describe each file in a Linux file system. The number of inodes sets how many files a partition can hold.
input: Data going into a computer, such as a key press or a barcode scan.
instruction: One small step a CPU can do, such as copy, add, compare or jump. A program is a long list of them.
instruction set: The list of instructions a CPU understands, such as x86-64 or ARM. A program is built for one instruction set.
integrated graphics: A GPU on the CPU chip that shares the system's RAM. It is plenty for office work and video.

J

journal: A file system's record of each change, made before the change itself. After a power cut it shows what to finish or undo.

K

kernel: The core of the operating system, with full control of the hardware. The bootloader loads it, and it loads the drivers and starts the services.
kibibyte (KiB): 1,024 bytes; each next unit (MiB, GiB, TiB) is 1,024 times the one before. Operating systems often count this way, which is why a '1 TB' disk shows as 931 GiB.
kilobyte (KB): 1,000 bytes; each next unit (MB, GB, TB) is 1,000 times the one before. Disk makers count this way.
known-good part: A spare you know works, swapped in to test a suspect part. If the fault moves with the part, the part is bad.

L

L1, L2, L3: The three cache levels. L1 is the smallest and fastest, one per core and split into data and instructions; L2 is bigger, usually one per core; L3 is the largest and shared by all cores.
lanes: PCIe's parallel data paths. A graphics card uses 16 (x16) and an NVMe SSD 4 (x4), and a connection's speed is the per-lane speed × the number of lanes.
laser printer: A printer that melts toner powder onto paper with heat. It is fast and cheap per page for office documents.
loop device: A file that Linux treats as a drive. Alex used one to practice partitioning and formatting kc-disk.img.
LPDDR: Low-power RAM that is soldered into thin laptops, phones and Macs. 'LPDDR' on a spec sheet means you can't upgrade the RAM later.
lscpu: Describes the CPU: model name, cores, threads per core, sockets and cache sizes.
lspci: Lists the devices on the PCIe bus, each with its bus address, its kind, and its maker and model.

M

M.2: Only a shape: a small stick that screws flat onto the motherboard, and its slot; some M.2 slots take only SATA sticks and some only NVMe. The size code 2280 means 22 mm wide and 80 mm long, the usual length.
MAC address: A network card's six-byte address, set by the maker and written in hex with colons, such as 02:fc:00:00:00:01.
machine code: Instructions stored as bytes that the CPU runs directly. It only means something to one instruction set.
malware: Harmful software. Malware that runs before the OS is the hardest to find, which is what Secure Boot prevents.
MBR: The old partition table (master boot record) from the 1980s: up to 4 partitions on drives up to 2 TiB. It goes with the old BIOS.
memory ladder: Registers, cache, RAM, SSD and hard drive in order. Each step down is bigger and cheaper per byte but slower.
memtest86+: A free memory tester you start from a USB stick. Windows Memory Diagnostic does the same check after a restart.
mirroring: Writing every change to two drives at once (RAID 1), so the machine keeps working if one drive dies.
modules: Small boards that hold RAM chips and push into slots on the motherboard.
motherboard: The main circuit board that connects every part: CPU socket, RAM slots, M.2 slots and expansion slots.
mounting: Attaching a file system to a folder so its files appear there; Linux has no drive letters. The command is mount, and umount (no 'n') detaches it.
MT/s: Millions of transfers per second, a RAM speed, as in DDR5-5600. MT/s × 8 bytes gives MB/s per module.
Multipass: A free program from Canonical that runs Ubuntu Linux virtual machines on Windows, macOS or Linux. For example, `multipass launch --name lab` creates a practice VM called `lab`, and `multipass shell lab` opens a terminal inside it.

N

nano: A simple text editor in the terminal. Ctrl+O saves and Ctrl+X quits.
NTFS: The Windows file system, with permissions and large files. macOS reads it but won't write it.
NVMe: The language SSDs use to talk over fast PCIe lanes, reaching about 7,000 to 14,000 MB/s. On Linux, NVMe drives are named nvme0n1 and so on.

O

operating system (OS): The program that starts first, controls the hardware and runs every other program, such as Windows, macOS or Linux.
output: Results coming out of a computer, such as a picture on screen or a printed label.

P

parity: Extra check data in RAID 5 that lets any one failed drive be rebuilt.
partitions: Separate areas of a drive, each acting like a drive of its own. A table at the start of the drive (GPT or MBR) lists where each one begins and ends.
PCIe: PCI Express, the fast bus for graphics cards and NVMe SSDs, built from lanes. Each generation roughly doubles the speed per lane, and mixed generations run at the slower one's speed.
performance cores, efficiency cores: Big, fast P-cores for heavy work and small, low-power E-cores for background jobs. In a spec such as '4P + 8E, 16 threads', only the P-cores run two threads each.
peripherals: Keyboards, mice, displays, printers and other attached input and output devices.
pipe: The | sign, which sends what one command prints into the next command, as in printf 'Kettle' | xxd.
pixels: The tiny dots that make up a screen's picture. Each one mixes red, green and blue light and is sent as 3 bytes.
POST: The power-on self-test the firmware runs first: it checks the CPU, RAM and graphics and finds the drives. A failure shows as beeps or lights.
power supply unit (PSU): Turns wall power into the steady 12 V, 5 V and 3.3 V the parts use. Size it at the parts' total watts plus about 30% headroom.
preventive measures: Changes that stop a fixed problem from coming back, like Alex moving Priya's PC out of the sun and adding desktop dusting to the checklist.
processing: Working on data, which is the CPU's job.
prompt: The shell's sign that it's ready for a command, such as ubuntu@lab:~$. Don't type the $ itself.

R

RAID: Combining several drives into one: for speed (RAID 0, which loses everything if a drive dies) or for safety (RAID 1, 5, 10). Kettle & Crane's backup box uses RAID 1, but RAID is not a backup.
RAM: Random access memory: fast, volatile working space holding what the CPU is working on now. Unsaved changes are lost when the power goes.
recovery key: The backup key BitLocker asks for when the TPM sees a changed boot chain, for example after a firmware update or drive swap. Keep it in the Microsoft account or IT records.
refresh rate: How many new pictures a second a screen shows, in Hz. 60 Hz is fine for office work, while 120 to 240 Hz is smoother for games and needs a faster cable.
register: A tiny storage slot inside the CPU. One register always holds the address of the next instruction.
resolution: A screen's size in pixels across × down, such as 1920 × 1200. Common names: Full HD (1920 × 1080, about 2.1 million pixels), QHD (2560 × 1440, about 3.7 million) and 4K or UHD (3840 × 2160, about 8.3 million).

S

SATA: The older connection designed for hard drives. It caps drives near 550 MB/s, so even the fastest SATA SSD stops there.
script: A text file of commands run as a program, such as busy.sh or inventory.sh.
sectors: The smallest numbered pieces a drive reads or writes, 512 bytes or 4 KiB. Partition tables list partitions by sector number.
Secure Boot: A UEFI feature that checks each bootloader's digital signature and only starts ones signed by a trusted maker. Windows 11 needs a PC that can do it.
sensors: Chips that measure temperatures and fan speeds, and also the Linux command (from the lm-sensors package) that reads them. A VM has none.
shebang: A script's first line, #!/bin/bash, which names the program that runs it.
shell: The program that reads your commands, such as bash. It can also do sums and run scripts.
six-step troubleshooting method: Identify the problem, establish a theory, test it, plan and fix, verify and prevent, then document. Change one thing at a time.
SO-DIMMs: The short RAM modules used in laptops. Jo's laptop got a second one.
SoC: System on a chip: one chip that holds the CPU cores, graphics and often RAM, as in phones and tablets. Nothing on it can be upgraded.
socket: The CPU's place on the motherboard, named like AM5 or LGA 1851; a CPU fits only a matching socket. In lscpu it also means one physical CPU chip.
software: Programs, as opposed to the hardware they run on.
soldered RAM: RAM fixed to the board, as in many thin laptops and all Apple silicon Macs. It can never be upgraded, so tess-lt was planned for replacement instead.
solid-state drive (SSD): Storage on flash memory chips with no moving parts: silent, shock-proof and fast, reaching any spot in about 100 microseconds.
storage: Where files stay with the power off: an SSD or hard drive. It is much slower than RAM.
striping: Splitting data across several drives for speed (RAID 0). If any one drive dies, everything is lost.
sudo: Runs one command as the administrator, for example sudo lshw or sudo dmesg.

T

Task Manager: The Windows app (Ctrl+Shift+Esc) whose Performance tab shows CPU, memory, slots, form factor and drive type. It is the main tool for finding a bottleneck.
TBW: Terabytes written: the SSD maker's limit on how much can be written before flash wears out. Office use rarely reaches it.
TDP: Thermal design power: the heat in watts that a CPU's cooler must remove. It is about 15 to 55 W for laptop chips and 65 to 170 W for desktop ones.
terminal: A window where you type commands instead of clicking, such as PowerShell on Windows or Terminal on a Mac.
thermal paste: A thin layer between a chip and its heatsink that fills tiny gaps so heat flows across. It can dry out after many years.
thermal throttling: A CPU slowing itself down because it's too hot, usually from dust in the vents, blocked vents or dried paste. A laptop that turns sluggish with a roaring fan is often throttling.
thread: One stream of instructions. Many cores can run two at once, using parts of the core the first thread leaves idle.
Thunderbolt: Intel's fast connection on the USB-C plug: Thunderbolt 4 runs at 40 Gb/s and Thunderbolt 5 at 80 Gb/s. A Thunderbolt port also works as a normal USB port.
TPM: Trusted platform module: a security chip, or part of the CPU, that stores keys and records what started at each boot stage. Windows 11 needs TPM 2.0, sometimes called PTT or fTPM in the firmware.

U

UEFI: Modern PC firmware that replaced the BIOS. It boots GPT drives, reads bootloaders from the EFI System Partition and supports Secure Boot.
USB: The common connection for keyboards, drives and phones. Ports are labeled by speed, from USB 2.0 (480 Mb/s) to USB 80Gbps.
USB Power Delivery: Charging a laptop over USB-C, up to 240 W with the right cable and charger.
USB-C: The small oval USB plug that fits either way up. Its speed and features (charging, display, Thunderbolt) depend on the port and cable, not the plug.
USB4: The USB generation running at 40 Gb/s, or 80 Gb/s in Version 2.0. It is fast enough for docks and monitors, like Sam's one-cable desk.
UUID: A unique ID given to every file system, which Linux uses to find it even if the drive's name changes.

V

variable: A named value in the shell or a script, such as n=0; $n gives its value.
virtual machine (VM): A computer that runs as a program inside another computer, using a share of the real machine's CPU, RAM and disk. VMs give you a safe, separate system to practise on, such as an Ubuntu VM called `lab` created with Multipass.
volatile: Losing its contents when the power goes off, like RAM.

W

Wi-Fi: Wireless networking; devices must share a generation to get full speed, and Wi-Fi 7 is the newest in use. The technical standard names are 802.11ac (Wi-Fi 5), 802.11ax (Wi-Fi 6 and 6E) and 802.11be (Wi-Fi 7).

X

x86-64: The instruction set of Intel and AMD chips, found in most Windows PCs and servers.