Glossary

This page provides a glossary of terms.

Summary

The Restart Wiki tries to assume no previous knowledge, only a willingness to learn, and so we try to introduce and explain technical terms as we go along. But you might dip in and out or read the end of an article before the beginning. So this page gathers together as many technical terms as possible, as a single point of reference.

If you prefer, you can also use your favourite search engine or Wikipedia to look up unfamiliar terms.

Glossary of Terms

0-9 A B C D E F G H I J K L M N O P Q R S T U V W XYZ

Term	Meaning
0 - 9
2FA	See Two factor Authentication.
A
AC	Alternating Current. An electrical supply which reverses direction many times per second. See AC and DC.
AC/DC motor	A type of electric motor that runs equally well on AC or DC. See DC and Universal (AC/DC) Motors.
AF	Audio Frequency. A frequency within the audible range of approximately 20Hz - 20kHz.
AM	Amplitude Modulation. A method of modulation in which the amplitude of an RF signal is modulated by the AF signal to be transmitted. See Amplitude Modulation.
Amps (A)	The unit of electric current, i.e. the quantity of electricity passing, a bit like the amount of water flowing in a river. See Electric circuits, volts amps watts and ohms.
Anode	A positive electrode.
B
Binary	A number system using only the digits 0 and 1, well suited to computers as they can represent those digits by the on and off states of a switch.
BIOS	Basic Input/Output System. A program built in to PCs up until around 2011, which controls the PC prior to booting and initiates the boot process. (Newer computers use UEFI). See BIOS vs UEFI.
Bit	A binary digit, representing one of two values or states, such as 1/0, or yes/no, or love/hate Marmite.
Bridge Rectifier	Four diodes connected in a square. Applying AC to two opposite corners, you get DC out of the other two. See Linear Power Supplies.
Brush	A small block of graphite, a pair of which feed the current to the rotor of an AC/DC motor via the commutator. See DC and Universal (AC/DC) Motors.
Byte	8 bits, which can be used to represent a single letter, number or punctuation mark, or a number between 0 and 255, or anything else that can have up to 256 values.
C
Capacitor	An electronic component which can store electric charge. Its capacitance is measured in Farads. See Capacitors.
Cathode	A negative electrode.
Circuit	Electricity really hates piling up, so it will only flow if it can go around a complete circuit and come back to where it started.
Circuit Diagram	A vacuum cleaner, for example, may contain several paths or "circuits" around which the current can flow, and a computer may contain a huge number. A circuit diagram is a picture of all those paths (or some of them) allowing you to understand how it works.
Commutator	Part of the rotor of an AC/DC motor which receives the current from the brushes. See DC and Universal (AC/DC) Motors.
CPU	Central Processing Unit. The "brains" of a computer, which executes a computer program.
D
DC	Direct Current. An electrical supply which goes in one direction only. See AC and DC.
Decimal	The number system we commonly use, based on the digits 0 - 9.
Diac	A 2-terminal electronic component which switches from a non-conducting to a conducting state when a certain voltage is applied, then remains conducting until the current is switched off. Commonly used in conjunction with a triac in dimmer switches.
DIL	Dual In-Line. A type of IC packaging with 2 parallel rows of pins, designed for through-hole assembly.
Diode	A 2 terminal electronic component allowing a current to flow in one direction but not the other. See Diodes and Rectifiers.
Distro	A flavour of Linux comprising a kernel, a desktop manager and a selection of utilities.
Demodulation	The process of recovering an audio or TV signal (for example) from the RF signal received from an aerial.
E
Earth loop	See Ground loop.
Electrode	An electrical conductor making contact with a non-metallic part of a circuit such as a semiconductor or the electrolyte in a battery.
Electrolyte	A conducting liquid containing negative and positive ions, such as the liquid in a battery
Electrolytic Capacitor	A type of capacitor which employs an electro-chemical process to achieve a high level of capacitance. See Capacitors.
Electron	A sub-atomic particle carrying a negative electrical charge. A flow of electrons constitutes an electric current.
Encryption	The process of transforming a message or data (the "cleartext") into a completely unintelligible form (the "ciphertext"). Only with knowledge of a secret key can the ciphertext be transformed back into the cleartext.
F
Farad	The unit of capacitance. See Capacitors.
Field Effect Transistor	A type of transistor where the current flowing between two of its terminals (the source and the drain) is controlled by an electric field created by a voltage on a third terminal (the gate). See Transistors.
Flux	A liquid or paste which helps to remove oxide or other deposits in order to make good solder joints. Only usually needed for challenging soldering jobs such as surface mount as solder normally contains a core of flux.
FM	Frequency Modulation. A method of modulation in which the frequencyof an RF signal is modulated by the AF signal to be transmitted. See Frequency Modulation.
Frequency	The number of complete (positive and negative) cycles of AC which occur per second. Measured in Hertz.
Full wave rectifier	A rectifier which uses both the positive and negative half cycles of the AC input to produce a DC output. Most often this is achieved with a bridge rectifier.
Fuse	A thin piece of low melting point wire designed to melt and so break the circuit if too much current flows due to a fault.
G
GB	Gigabyte: 1000 megabytes, but often used for 1024 megabytes, which is more properly written GiB.
GHz	A billion Hz
GPT	GUID Partition Table. The name given to newer method of organising the contents of a disk. SeeMBR vs GPT disk layout.
Ground loop	When two pieces of audio equipment are connected together, each having its own earth connection, some of the small current that should be going from one of the pieces of equipment to its own earth connection instead goes via the connection to the other equipment's earth, causing an objectionable hum in the audio output.
GUID	Globally Unique IDentifier. A 128 bit used for identifying various types of resource in a computer suystem.
H
Hard Disk	A computer's main long term storage, which is held on rapidly spinning magnetic disk.
Hardware	The physical electronic and electromechanical parts which comprise a computer.
Half wave rectifier	A rectifier which uses only the positive (or the negative) half cycles of the AC input to produce a DC output, by using a single diode.
HD	See Hard Disk
Henry	The unit of inductance. See Inductors.
Hertz (Hz)	The measure of frequency.
Hexadecimal	A number system based on only 16 digits which are represented by 0-9 and A - F. This is useful because each hexadecimal digit can represent 4 bits and 2 hexadecimal digits can represent 8 bits or a byte.
Hole	The lack of an electron in a crystal lattice where there should be one. This leaves behind a positive charge. An electron from an adjacent atom can move into the hole causing the hole to move to the adjacent atom. In this way, holes can act like positively charged particles and carry an electric current.
Hum	A constant low frequency sound in the output of audio equipment due (for example) to inadequate smoothing in the power supply and residual ripple in its output, or to the presence of a ground loop.
Hz	See Hertz.
I
IC	Integrated Circuit. A circuit comprising anything from dozens to billions of electronic components, all fabricated on a single silicon chip. See Integrated Circuits.
IF	Intermediate Frequency. A frequency between the RF and AF in a superhet radio at which most of the amplification and selection of the required station occurs.
Induction motor	A type of electric motor, often used in fans, which only runs on AC. See Induction Motors.
Inductor	A coil of wire, very often wound around a magnetic core, providing a kind of momentum to the flow of electricity. Its inductance is measured in Henrys. See Inductors.
Integrated Circuit	See IC.
Ion	A positively or negatively charged atom.
J
jFET	Junction Field Effect Transistor. A type of field effect transistor where the gate is formed by a semiconductor junction. See Transistors.
Junction Transistor	A type of transistor with 3 semiconductor layers. See Transistors.
K
kB	Kilobyte: 1024 bytes.
Kernel	The core of an operating system, which concerns itself with managing the hardware resources at the lowest level. It normally has no user interface but rather provides services based on those resources to other programs, some of which will themselves have a user interface.
kHz	1,000 Hz
L
LED	Light Emitting Diode.
Linear Regulator	A circuit often in the form of an IC which produces a constant well defined voltage from a variable or poorly defined higher voltage input, simply by absorbing excess and turning it into heat. See Linear Power Supplies.
Linux	A free, open source operating system kernel which, packaged into a distro, you can use as an alternative to Windows or OS/X.
Live Linux	Linux on a bootable CD/DVD or memory stick which can be run from that media without affecting the installed operating system on the hard disk.
Loupe	A magnifying glass, generally without a handle.
M
Malware	Any bad piece of software which attempts to get onto your computer for malicious purposes.
MB	Megabyte: 1000 kilobytes, but often used for 1024 kilobytes, which is more properly written MiB.
MBR	Master Boot Record. The name given to an older method of organising the contents of a disk. SeeMBR vs GPT disk layout.
MHz	A million Hz
Modulation	The process of impressing an audio or TV signal (for example) an RF signal for transmission.
MOSFET	Metal Oxide Field Effect Transistor. A type of field effect transistor where the gate is formed by metal deposited on an extremely thin insulating oxide layer. See Transistors.
Multimeter	An electrical test instrument which measures voltage, current, resistance and often several other things. Most usually they have a digital readout but analogue ones with a dial are also available.
N
O
Object Code	Software in a form that can be directly executed by a computer, but is virtually unintelligible to humans, simply comprising binary numbers.
Octal	A number system based on only 8 digits 0 - 7. This is useful because each octal digit can represent 3 bits.
Ohms (Ω)	A bit like friction, the unit of resistance to flow of electricity. See Electric circuits, volts amps watts and ohms.
Ohm's Law	The amount of current (Amps) flowing in a circuit is the pressure (Volts) divided by the resistance (Ohms), or I = V / R.
Open Circuit	Electricity likes to go all the way round a circuit and back to where it started. When there is a break in the circuit preventing the current from flowing (maybe due to a fault) this is termed an open circuit.
Open Source	Software or hardware the source code or design of which is non-proprietary and made freely available for anyone to inspect or modify for their own purposes.
Operating System	The software which manages the computing, storage and communications resources of a computer, and presents a user interface allowing the user to run and interact with programs as desired.
Opto coupler	An LED and a phototransistor, electrically isolated but in a single packaged. Used for signalling between two circuits which must have no electrical connection between them.
Oscillator	A circuit which produces an AC output at a chosen frequency.
P
Password Manager	A program or app which stores all your passwords in an encrypted vault under a (hopefully) strong master password. This make it possible to use very strong totally random and unguessable passwords, which most password managers will generate for you.
PAT Test	Portable Appliance Test. This is a basic electrical safety test which should be applied to alll mains operated electrical equipment before and after attempting a repair. It comprises a visual inspection and an automated test. See PAT testing for more details.
Phillips	A type of cross-head screw or screwdriver, similar to but not quite the same as Posidriv.
Phishing	The criminal practice of sending emails or messages through social media inviting the recipient to open a malicious attachment or visit a malicious website.
Phototransistor	A light-sensitive transistor used for sensing light.
Posidriv	A type of cross-head screw or screwdriver, similar to but not quite the same as Phillips.
Potentiometer (or Pot)	A resistor with a slider than can be moved along its length from one end to the other to tap off any required amount of resistance, for example for a volume control. See Potentiometer.
Primary Battery	A single-use battery.
PUP	Potentially Unwanted Program. Any useless but generally (though not necessarily) harmless program, generally installed by the computer vendor, or (knowingly or unknowingly) installed along with downloaded software, the main purpose of which is generally to sell you some other software which you probably don't want.
Q
R
RAM	Random Access Memory. Very fast memory used by a computer as working store for data and programs currently being processed.
Ransomware	Malware which encrypts all your files then demands a ransom in order to recover them for you.
Rectifier	A diode used for converting AC to DC.
Reservoir Capacitor	A large value capacitor used in a power supply for smoothing.
Resistor	An electronic component which resists the flow of electricity. It's resistance is measured in Ohms. A resistor always generates heat, even if only a tiny amount, and any replacement must be rated in Watts accordingly. See Resistors.
Resistance	See Ohms.
RF	Radio Frequency. A high frequency capable of being transmitted as a radio signal.
Ripple	Residual variation after smoothing in the voltage of a DC power supply at the frequency or twice the frequency of the AC mains input.
S
Schematic	Another name for a Circuit Diagram.
SCR	Silicon Controlled Rectifier. See Thyristor.
Semiconductor	A material such as silicon, germanium or gallium arsenide which can be made to conduct electricity either by negatively charged electrons (N-type) or by positively charged holes (P-type), by adding small amounts of carefully chosen impurities.
Secondary Battery	A rechargeable battery.
Sector	The smallest block of data a disk can read or write. On older disks this was normally 512 bytes but in modern disks and SSDs it is usually 4096 bytes.
Short circuit	If two wires are touching which shouldn't the electricity may be able to take a short cut, meeting very little resistance and so allowing too much electricity to flow. This is a Bad Thing and can cause things to get hot or even catch fire.
Shottky diode	A type of diode using a metal-semiconductor junction, mainly used in switching mode power supplies on account of its ability to operate efficiently at higher frequencies.
SIL	Single In-Line. A type of packaging used for circuit sub-assemblies, resistor networks and some ICs with a single row of pins, designed for through-hole assembly.
S.M.A.R.T	Self-Monitoring, Analysis, and Reporting Technology. A technology built into all modern hard disks and solid state disks by which the device can monitor things like its error rate in order to report back and hopefully give early warning of impending failure.
Smoothing	The process of turning raw rectified AC, which drops to zero twice in every cycle of the AC, into a reasonably constant voltage. See Why is a power supply needed?.
Software	The step-by-step instructions which tell a computer what to do and how to do it.
Solder	A mixture (most often) of tin and copper or lead with a relatively low melting point, making it very convenient for making electrical connections.
Solid State Disk	A faster (though more expensive) alternative to a hard disk for a computer's long term storage.
Source Code	Software in a human-readable form as created by a developer. Generally, this cannot be directly be understood or run by a computer, but has translated by a special program called a compiler into object code.
Spear Phishing	A type of phishing attack directed at a specific victim who has probably been researched in order to make the attack seem highly plausible.
Spudger	A tool with a thin plastic or metal blade typically used (for example) for inserting into the crack between two halves of a plastic case in order to pry it open.
SSD	See Solid State Disk.
Superhet	A common design of radio receiver. See Superhet.
Surface Mount	A method of manufacture in which electronic components are soldered directly onto the surface of a printed circuit board, as opposed to the older through-hole method.
Switch-mode Regulator	A circuit which produces a constant well defined voltage from a variable or poorly defined voltage input, by switching the power on and off very rapidly and smoothing the result. See Switching Mode Power Supplies.
Synchronous motor	A type of electric motor which only runs on AC, and which runs at a speed which is locked to the AC supply frequency. See Synchronous Motors.
T
TB	Terabyte: 1000 gigabytes, but often used for 1024 gigabytes, which is more properly written TiB.
Thermistor	An electronic component like a resistor but with a resistance which decreases substantially with increasing temperature.
Through-hole	A method of manufacture in which electronic components are attached to a circuit board by passing their leads or pins through holes in the board and soldering them to the board on the other side, as opposed to the more modern surface mount technique which allows much higher component densities.
Thyristor	An electronic component with 3 leads used as a switch. Also known as a Silicon Controlled Rectifier. See Transistors.
Transformer	Two (or more) coils of wire wound around a magnetic core, used to step a voltage up or down or provide isolation between two circuits. See Transformers.
Transistor	An electronic component with 3 leads used to amplify a signal or switch a current on or off. See Transistors.
Triac	A type of thyristor which, unlike the standard type, can be used on AC. Commonly used in dimmer switches.
Torx	A type of security screw or screwdriver with a 6-pointed star shape.
Two Factor Authentication	A login scheme where you are required to supply not only a password ("something you know") but also prove your possession of a token of some sort ("something you have") or provide a biometric such as a fingerprint ("something you are").
Tuned Circuit	A capacitor and an inductor connected together, which resonate at a particular frequency.
Two Step Authentication	A kind of "poor man's Two factor Authentication" where the second factor is a one time code delivered to you by text message. Whilst considerably better than a password on its own, this is no longer greatly recommended on account of the relative ease by which a determined criminal could get a SIM card registered to your phone number
U
UEFI	Unified Extensible Firmware Interface. A program built in to newer PCs (since around 2011) which controls the PC prior to booting and initiates the boot process. (Older computers used BIOS). See BIOS vs UEFI.
Universal motor	A type of electric motor that runs equally well on AC or DC. See DC and Universal (AC/DC) Motors.
V
Virus	A term commonly used for any type of malware, but strictly meaning self-replicating malware.
Volts (V)	The unit of electrical pressure, a bit like water pressure. See Electric circuits, volts amps watts and ohms.
Vulnerability	A flaw in a website or software product by which it can be compromised for malicious purposes, such as spreading malware.
W
Watts (W)	The unit of power, calculated by multiplying the Volts by the Amps. See Electric circuits, volts amps watts and ohms.
Wavelength	The distance between successive crests of a radio wave as it travels through the air. See Freqvency vs wavelength.
Worm	A type of malware able to spread across a network, or the whole Internet.
XYZ
Zener diode	A type of diode which starts conducting in the reverse (normally non-conducting) direction at a well defined voltage.