Wiki

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 [https://en.wikipedia.org/wiki/Main_Page Wikipedia] to look up unfamiliar terms.

==Glossary of Terms==
{| class="wikitable"
|'''Term'''
|'''Meaning'''

|-
|2FA
|
See [[#Two Factor Authentication|Two factor Authentication]].

|-
|<span id="AC">AC</span>
|
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|AC]] or [[#DC|DC]]. See [[Electric_motors#DC_and_Universal_.28AC.2FDC.29_Motors|DC and Universal (AC/DC) Motors]].

|-
|<span id="AF">AF</span>
|
Audio Frequency. A [[#Frequency|frequency]] within the audible range of approximately 20[[#Hz|Hz]] - 20[[#kHz|kHz]].

|-
|AM
|
Amplitude Modulation. A method of [[#Modulation|modulation]] in which the amplitude of an [[#RF|RF]] signal is modulated by the [[##AF|AF]] signal to be transmitted. See [[How_radios_work#Amplitude_Modulation_.28AM.29|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|electrode]].

|-
|<span id="Bit">Bit</span>
|
A binary digit, representing one of two values or states, such as 1 or 0, or yes or no.

|-
|<span id="Bridge Rectifier">Bridge Rectifier</span>
|
Four [[#Diode|diodes]] connected in a square. Applying [[#AC|AC]] to two opposite corners, you get [[#DC|DC]] out of the other two. See [[Power_supplies#Linear_Power_Supplies|Linear Power Supplies]].

|-
|<span -d="Brush">Brush</span>
|
A small block of graphite, a pair of which feed the current to the rotor of an AC/DC motor via the [[#Commutator|commutator]]. See [[Electric_motors#DC_and_Universal_.28AC.2FDC.29_Motors|DC and Universal (AC/DC) Motors]].

|-
|<span id="Byte">Byte</span>
|
8 [[#Bit|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.

|-
|<span id="Capacitor">Capacitor</span>
|
An electronic component which can store electric charge. Its capacitance is measured in [[#Farad|Farads]]. See [[Basic electronic components#Capacitors|Capacitors]].

|-
|Cathode
|
A negative [[#Electrode|electrode]].

|-
|<span id="Circuit">Circuit</span>
|
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.

|-
|<span id="Circuit Diagram">Circuit Diagram</span>
|
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.

|-
|<span id="Commutator">Commutator</span>
|
Part of the rotor of an AC/DC motor which receives the current from the [[#Brush|brushes]]. See [[Electric_motors#DC_and_Universal_.28AC.2FDC.29_Motors|DC and Universal (AC/DC) Motors]].

|-
|CPU
|
Central Processing Unit. The "brains" of a computer, which executes a computer program.

|-
|<span id="DC">DC</span>
|
Direct Current. An electrical supply which goes in one direction only. See [[AC and DC]].

|-
|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|triac]] in dimmer switches.

|-
|DIL
|
Dual In-Line. A type of [[#IC|IC]] packaging with 2 parallel rows of pins, designed for [[#Through-hole|through-hole]] assembly.

|-
|<span id="Diode">Diode</span>
|
A 2 terminal electronic component allowing a current to flow in one direction but not the other. See [[Active_components#Diodes_and_Rectifiers|Diodes and Rectifiers]].

|-
|<span id="Demodulation">Demodulation</span>
|
The process of recovering an audio or TV signal (for example) from the [[#RF|RF]] signal received from an aerial.

|-
|Earth loop
|
See [[#Ground loop|Ground loop]].

|-
|<span id="Electrode">Electrode</span>
|
An electrical conductor making contact with a non-metallic part of a circuit such as a [[#Semiconductor|semiconductor]] or the [[#Electrolyte|electrolyte]] in a battery.

|-
|<span id="Electrolyte">Electrolyte</span>
|
A conducting liquid containing negative and positive [[#Ion|ions]], such as the liquid in a battery

|-
|Electrolytic Capacitor
|
A type of [[#Capacitor|capacitor]] which employs an electro-chemical process to achieve a high level of capacitance. See [[Basic electronic components#Capacitors|Capacitors]].

|-
|<span id="Electron">Electron</span>
|
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.

|-
|<span id="Farad">Farad</span>
|
The unit of capacitance. See [[Basic electronic components#Capacitors|Capacitors]].

|-
|<span id="FET">Field Effect Transistor</span>
|
A type of [[#Transistor|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 [[Active_components#Transistors|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|surface mount]] as solder normally contains a core of flux.

|-
|FM
|
Frequency Modulation. A method of [[#Modulation|modulation]] in which the [[#Frequency|frequency]]of an [[#RF|RF]] signal is modulated by the [[#AF|AF]] signal to be transmitted. See [[How_radios_work#Frequency_Modulation_.28FM.29|Frequency Modulation]].

|-
|<span id="Frequency">Frequency</span>
|
The number of complete (positive and negative) cycles of [[#AC|AC]] which occur per second. Measured in [[#Hertz|Hertz]].

|-
|Full wave rectifier
|
A [[#Rectifier|rectifier]] which uses both the positive and negative half cycles of the [[#AC|AC]] input to produce a [[#DC|DC]] output. Most often this is achieved with a [[#Bridge Rectifier|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.

|-
|<span id="GB">GB</span>
|
Gigabyte: 1000 [[#MB|megabytes]], but often used for 1024 [[#MB|megabytes]], which is more properly written GiB.

|-
|<span id="GHz">GHz</span>
|
A billion [[#Hertz|Hz]]

|-
|<span id="Ground loop">Ground loop</span>
|
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|hum]] in the audio output.

|-
|<span id="Hard Disk">Hard Disk</span>
|
A computer's main long term storage, which is held on  rapidly spinning magnetic disk.

|-
|Half wave rectifier
|
A [[#Rectifier|rectifier]] which uses only the positive (or the negative) half cycles of the [[#AC|AC]] input to produce a [[#DC|DC]] output, by using a single [[#Diode|diode]].

|-
|HD
|
See [[#Hard Disk|Hard Disk]]

|-
|<span id="Hertz">Hertz (Hz)</span>
|
The measure of [[#Frequency|frequency]].

|-
|<span id="Henry">Henry</span>
|
The unit of inductance. See [[Basic electronic components#Inductors|Inductors]].

|-
|Hole
|
The lack of an [[#Electron|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.

|-
|<span id="Hum">Hum</span>
|
A constant low frequency sound in the output of audio equipment due (for example) to inadequate [[#Smoothing|smoothing]] in the [[#Power supplies|power supply]] and residual [[#Ripple|ripple]] in its output, or to the presence of a [[#Ground loop|ground loop]].

|-
|Hz
|
See [[#Hertz|Hertz]].

|-
|<span id="IC">IC</span>
|
Integrated Circuit. A circuit comprising anything from dozens to billions of electronic components, all fabricated on a single silicon chip. See [[Active_components#Integrated_Circuits|Integrated Circuits]].

|-
|IF
|
Intermediate Frequency. A [[#Frequency|frequency]] between the [[#RF|RF]] and [[#AF|AF]] in a [[#Superhet|superhet]] radio at which most of the amplification and selection of the required station occurs.

|-
|<span id="Inductor">Inductor</span>
|
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 [[#Henry|Henrys]]. See [[Basic electronic components#Inductors|Inductors]].

|-
|Integrated Circuit
|
See [[#IC|IC]].

|-
|<span id="Ion">Ion</span>
|
A positively or negatively charged atom.

|-
|jFET
|
Junction Field Effect Transistor. A type of [[#FET|field effect transistor]] where the gate is formed by a [[#Semiconductor|semiconductor]] junction. See [[Active_components#Transistors|Transistors]].

|-
|Junction Transistor
|
A type of [[#Transistor|transistor]] with 3 [[#Semiconductor|semiconductor]] layers. See [[Active_components#Transistors|Transistors]].

|-
|<span id="kB">kB</span>
|
Kilobyte: 1024 [[#Byte|bytes]].

|-
|<span id="kHz">kHz</span>
|
1,000 [[#Hertz|Hz]]

|-
|LED
|
Light Emitting [[#Diode|Diode]].

|-
|Linear Regulator
|
A [[#Circuit|circuit]] often in the form of an [[#IC|IC]] which produces a constant well defined [[#Volts|voltage]] from a variable or poorly defined higher voltage input, simply by absorbing excess and turning it into heat. See [[Power_supplies#Linear_Power_Supplies|Linear Power Supplies]].

|-
|Loupe
|
A magnifying glass, generally without a handle.

|-
|<span id="Malware">Malware</span>
|
Any bad piece of software which attempts to get onto your computer for malicious purposes.

|-
|<span id="MB">MB</span>
|
Megabyte: 1000 [[#kB|kilobytes]], but often used for 1024 [[#kB|kilobytes]], which is more properly written MiB.

|-
|<span id="MHz">MHz</span>
|
A million [[#Hertz|Hz]]

|-
|<span id="Modulation">Modulation</span>
|
The process of impressing an audio or TV signal (for example) an [[#RF|RF]] signal for transmission.

|-
|MOSFET
|
Metal Oxide Field Effect Transistor. A type of [[#FET|field effect transistor]] where the gate is formed by metal deposited on an extremely thin insulating oxide layer. See [[Active_components#Transistors|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.

|-
|<span id="Ohms">Ohms (Ω)</span>
|
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.

|-
|Opto coupler
|
An [[#LED|LED]] and a [[#Phototransistor|phototransistor]], electrically isolated but in a single packaged. Used for signalling between two [[#Circuit|circuits]] which must have no electrical connection between them.

|-
|Oscillator
|
A [[#Circuit|circuit]] which produces an [[#AC|AC]] output at a chosen [[#Frequency|frequency]].

|-
|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.

|-
|<span id="Phillips">Phillips</span>
|
A type of cross-head screw or screwdriver, similar to but not quite the same as [[#Posidriv|Posidriv]].

|-
|<span id="Phishing">Phishing</span>
|
The criminal practice of sending emails or messages through social media inviting the recipient to open a malicious attachment or visit a malicious website.

|-
|<span id="Phototransistor">Phototransistor</span>
|
A light-sensitive [[#Transistor|transistor]] used for sensing light.

|-
|<span id="Posidriv">Posidriv</span>
|
A type of cross-head screw or screwdriver, similar to but not quite the same as [[#Phillips|Phillips]].

|-
|Potentiometer (or Pot)
|
A [[#Resistor|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 [[Basic electronic components#Potentiometers|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.

|-
|RAM
|
Random Access Memory. Very fast memory used by a computer as working store for data and programs currently being processed.

|-
|Ransomware
|
[[#Malware|Malware]] which encrypts all your files then demands a ransom in order to recover them for you.

|-
|<span id="Rectifier">Rectifier</span>
|
A [[#Diode|diode]] used for converting [[#AC|AC]] to [[#DC|DC]].

|-
|Reservoir Capacitor
|
A large value [[#Capacitor|capacitor]] used in a [[Power supplies|power supply]] for [[#Smoothing|smoothing]].

|-
|<span id="Resistor">Resistor</span>
|
An electronic component which resists the flow of electricity. It's resistance is measured in [[#Ohms|Ohms]]. A resistor always generates heat, even if only a tiny amount, and any replacement must be rated in [[#Watt|Watts]] accordingly. See [[Basic electronic components#Resistors|Resistors]].

|-
|Resistance
|
See [[#Ohms|Ohms]].

|-
|<span id="RF">RF</span>
|
Radio Frequency. A high [[#Frequency|frequency]] capable of being transmitted as a radio signal.

|-
|<span id="Ripple">Ripple</span>
|
Residual variation after [[#Smoothing|smoothing]] in the [[#Volts|voltage]] of a [[#DC|DC]] power supply at the frequency or twice the frequency of the [[#AC|AC]] mains input.

|-
|Schematic
|
Another name for a [[#Circuit Diagram|Circuit Diagram]].

|-
|SCR
|
Silicon Controlled Rectifier. See [[#Thyristor|Thyristor]].

|-
|<span id="Semiconductor">Semiconductor</span>
|
A material such as silicon, germanium or gallium arsenide which can be made to conduct electricity either by negatively charged [[#Electron|electrons]] (N-type) or by positively charged [[#Hole|holes]] (P-type), by adding small amounts of carefully chosen impurities.

|-
|Secondary Battery
|
A rechargeable battery.

|-
|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|semiconductor]] junction, mainly used in [[Power_supplies#Switching_Mode_Power_Supplies|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|resistor]] networks and some [[#IC|IC]]s with a single row of pins, designed for [[#Through-hole|through-hole]] assembly.

|-
|S.M.A.R.T
|
Self-Monitoring, Analysis, and Reporting Technology. A technology built into all modern [[#Hard Disk|hard disks]] and [[#SSD|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.

|-
|<span id="Smoothing">Smoothing</span>
|
The process of turning raw rectified [[#AC|AC]], which drops to zero twice in every cycle of the AC, into a reasonably constant [[#Volts|voltage]]. See [[Power_supplies#Why_is_a_power_supply_needed.3F|Why is a power supply needed?]].

|-
|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.

|-
|<span id="Solid State Disk">Solid State Disk</span>
|
A faster (though more expensive) alternative to a [[#Hard Disk|hard disk]] for a computer's long term storage.

|-
|Spear Phishing
|
A type of [[#Phishing|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|Solid State Disk]].

|-
|<span id="Superhet">Superhet</span>
|
A common design of radio receiver. See [[How_radios_work#Superhet|Superhet]].

|-
|<span id="Surface_Mount">Surface Mount</span>
|
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|through-hole]] method.

|-
|Switch-mode Regulator
|
A [[#Circuit|circuit]] which produces a constant well defined [[#Volts|voltage]] from a variable or poorly defined voltage input, by switching the power on and off very rapidly and [[#Smoothing|smoothing]] the result. See [[Power_supplies#Switching_Mode_Power_Supplies|Switching Mode Power Supplies]].

|-
|<span id="TB">TB</span>
|
Terabyte: 1000 [[#GB|gigabytes]], but often used for 1024 [[#GB|gigabytes]], which is more properly written TiB.

|-
|Thermistor
|
An electronic component like a [[#Resistor|resistor]] but with a resistance which decreases substantially with increasing temperature.

|-
|<span id="Through-hole">Through-hole</span>
|
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|surface mount]] technique which allows much higher component densities.

|-
|<span id="Thyristor">Thyristor</span>
|
An electronic component with 3 leads used as a switch. Also known as a Silicon Controlled Rectifier. See [[Active_components#Transistors|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 [[Basic electronic components#Transformers|Transformers]].

|-
|<span id="Transistor">Transistor</span>
|
An electronic component with 3 leads used to amplify a signal or switch a current on or off. See [[Active_components#Transistors|Transistors]].

|-
|<span id="Triac">Triac</span>
|
A type of [[#Thyristor|thyristor]] which, unlike the standard type, can be used on [[#AC|AC]]. Commonly used in dimmer switches.

|-
|Torx
|
A type of security screw or screwdriver with a 6-pointed star shape.

|-
|<span id="Two Factor Authentication">Two Factor Authentication</span>
|
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|capacitor]] and an [[#Inductor|inductor]] connected together, which resonate at a particular [[#Frequency|frequency]].

|-
|Two Step Authentication
|
A kind of "poor man's [[#Two Factor Authentication|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

|-
|Universal motor
|
A type of electric motor that runs equally well on [[#AC|AC]] or [[#DC|DC]]. See [[Electric_motors#DC_and_Universal_.28AC.2FDC.29_Motors|DC and Universal (AC/DC) Motors]].

|-
|Virus
|
A term commonly used for any type of [[#Malware|malware]], but strictly meaning self-replicating malware.

|-
|<span id="Volts">Volts (V)</span>
|
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|malware]].

|-
|<span id="Watt">Watts (W)</span>
|
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 [[How_radios_work#Frequency_vs_wavelength|Freqvency vs wavelength]].

|-
|Worm
|
A type of [[#Malware|malware]] able to spread across a network, or the whole Internet.

|-
|Zener diode
|
A type of [[#Diode|diode]] which starts conducting in the reverse (normally non-conducting) direction at a well defined voltage.

|}

[[Category:General]]