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

Term	Meaning
AC	Alternating Current. An electrical supply which reverses direction many times per second. See AC and DC.
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.
Capacitor	An electronic component which can store electric charge. Its capacitance is measured in Farads. See Capacitors.
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.
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.
CPU	Central Processing Unit. The "brains" of a computer, which executes a computer program.
DC	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 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.
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.
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.
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.
Hard Disk	A computer's main long term storage, which is held on rapidly spinning magnetic disk.
HD	See Hard Disk
Henry	The unit of inductance. See Inductors.
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.
IC	Integrated Circuit. A circuit comprising anything from dozens to billions of electronic components, all fabricated on a single silicon chip. See Integrated Circuits.
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.
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.
LED	Light Emitting Diode.
Loupe	A magnifying glass, generally without a handle.
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.
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.
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.
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.
RAM	Random Access Memory. Very fast memory used by a computer as working store for data and programs currently being processed.
Rectifier	See Diode.
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.
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.
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.
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.
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.
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.
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.
Volts (V)	The unit of electrical pressure, a bit like water pressure. See Electric circuits, volts amps watts and ohms.
Watts (W)	The unit of power, calculated by multiplying the Volts by the Amps. See Electric circuits, volts amps watts and ohms.
Zener diode	A type of diode which starts conducting in the reverse (normally non-conducting) direction at a well defined voltage.