Item Definition 
 AC  Alternating Current. Used as mains power supply running at 240V (in Australia)
 Amps  Unit of measurement of electric current represented by the symbol A
 Analog  A system whereby the value of something is represented by a continuously changing physical quantity that can be measured. Radio, television, telephony, film and recordable media were all originally analog based. Unfortunately, analog reproductions will lose quality over time and multiple playbacks. Cassette tapes and vinyl records are examples of analog media that were replaced by digital media like CDs
 Binary  The numerical system of computers. Something is either in a 0 (off or low voltage) state or a 1 (on or high voltage) state and at its fundamental level, all computer logic is derived from this. Counting goes in twos instead of tens, so our (decimal) number 13 for example is 1101 in binary (1 x eight, 1 x four, 0 x two and 1 x one)
 BIOS  Basic Input Output System. The first thing that loads on your computer, which lives in firmware on your motherboard. This controls the devices connected to the computer, the boot order and other low-level functions. Can be updated by a process called “flashing”
 Bit  A representation of a 0 or 1, the smallest piece of information in computer terms. Short for Binary Digit
 Blu-ray (BD)  Superseded DVDs. Uses a blue laser instead of a red one. Blue light has a shorter wavelength than red light and a narrower beam, meaning it can focus on smaller areas, therefore data can be stored at a much higher density. Can hold 50Gb of data on a dual layer disk
 Byte  Traditionally 8 bits, the amount of information used to store a character. It is the smallest addressable unit of information in most computer systems
 Capacitor A device that holds a charge in an electronic circuit
 CD-ROM  Compact Disk-Read Only Memory – Optical media read by a laser. This format superseded floppy disks because it was much faster and had much higher capacity at just over 600Mb as opposed to 1.44Mb for a high density 3.5″ floppy disk
 CPU  Central Processing Unit. Effectively the brain of the computer which performs logical and arithmetical functions. The number of instructions that can be processed per second by the CPU is reckoned in GHz. For example, an Intel I7 4770 processor is quad-core and runs at 3.90 GHz. This means it can process 8 instructions (2 x 4 cores hyperthreaded) 3,900,000,000 times a second. Try doing that on an abacus!
 Current  Electrical current, the flow of electrons from two points in an electronic circuit, represented by the symbol I
 DC  Direct Current. Used to power computer components, which run at lower voltage to avoided overheating and consume less power
 Decimal  The numerical system of humans. 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9. The number 10 is simply the start of the next cycle, one 10, zero units.
 DHCP  Dynamic Host Configuration Protocol. A method for automatically assigning an IP address to a device based on a predefined scope and other parameters
 Digital  A discrete representation of information, usually in binary form. Real world information needs to be converted to digital in a process called sampling or quantisation. Once a digital reproduction is complete, this can be duplicated almost indefinitely without loss of quality or data
 DNS  Domain Name System. A system that provides friendly hierarchical names to a computer, device, system or resource on a network. For example DNS can resolve a name like to its IP address
 Download  The process of copying a file from a remote location to a local one
 DVD  Digital Versatile Disk. Superseded CDs. Has a capacity of 4.3Gb (8.6Gb dual layer), about 7-14 times the capacity of a CD.
 DVI  Digital Visual Interface. Wider and flatter than a VGA connector, a DVI connector is recognisable by its white colour
 Email  Electronic mail.
 FDD  Floppy Disk Drive. Came in 2 sizes, 5.25″ (which was flexible and had a capacity of 360k or 1.2 Mb) and 3.5″ (which was not and had a capacity of 1.44Mb). JAZ and ZIP drives appeared on the scene briefly but floppies were ultimately superseded by CDs
 Firewire (1394)  Similar to USB, introduced by Apple in the late 80s. USB has now all but replaced it
 Firmware  A computer program that drives a device for that purpose only. Mobile phones, modems, disk drives, TVs etc. are all controlled by firmware
 FTP  File Transfer Protocol. Part of the TCP/IP stack that allows transfer of files from a local system to a remote one and vice versa
 Gigabyte  One thousand Megabytes (1 billion bytes)
 Graphics Card  An add-on card that supplies higher end graphics capabilities. Comes with its own processor (GPU), is usually powered and has one or more fans. It takes the load off the CPU and performs graphical functions with specialised hardware
 Hardware  The physical devices that make up a computer system. Can include a motherboard, RAM, disk drives, etc
 HDD  Hard Disk Drive. The traditional types work by having a series of moveable read/write heads with multiple disk platters. Unlike RAM, data is persistent in that it is not lost when the power is switched off
 HDMI  High Definition Multimedia Interface. High level video and audio used in home theatre and also modern computer monitors
 Hertz  The metric unit of Frequency. Usually expressed as MHz (Megahertz) or GHz (Gigahertz). The number of cycles per second in millions or billions.
 Hexadecimal  Another numerical system used by computers. The base is 16 and represented by the numbers 0-9 and the letters A-F. As 16 = 24 it is easier and more readable to represent some numbers this way, most typically memory and MAC addresses
 IDE  Integrated Drive Electronics. Superseded by SATA. These were the old style flat ribbon cables used to connect hard disk drives to the motherboard. These were a nightmare, as it was quite easy to bend the connecting pins
 IMAP  Internet Message Access Protocol is a protocol used by email systems to download email but allows multiple connections and the ability to work online or offline and to synchronise email between multiple connections
 Integrated Circuit  Also known as a silicon chip. Silicon, as a semiconductor and one of the most abundant elements on this planet, is ideal as a base for transistors. They are now so advanced that tens of billions of transistors can fit on a single chip
 Internet  The world’s largest network. The forerunner, ARPANET was originally developed by Stanford University in the 1970s it has now evolved into the World Wide Web we know (and love) today
 IP Address  Internet Protocol address. An IP v4 address is a unique 32 bit address on a network represented in digital notation by 4 octets of numbers from 0-255 separated by a “.” IP v6 uses a 128 bit address where the numbers are written in hexadecimal format. There are special ranges of private IP addresses that are used on internal networks. These are 10.x.x.x, 172.16.x.x, 192.168.x.x and are not addressable on public networks. Usually routers on private networks at home will use one of the addresses as its IP address, for example
 ISA bus  Industry Standard Architecture. A type of computer bus architecture, now rendered obsolete by PCI. A bus, in computer terms is the connection between a devices inside a computer, or in the case of an ISA or PCI bus, the add-on card and the motherboard
 Keyboard  Device connected to the computer that allows input of characters
 Kilobyte  One thousand bytes. Or more accurately 210=1024 bytes
 LAN  Local Area Network. Devices connected together on the same network.
 LED  Light Emitting Diode. Used early on as indicator lights but can now be used as a low power efficient light source as well
 MAC Address  Media Access Control Address. Every network device in the world has a unique MAC address represented by a 12 digit hexadecimal number. For example: 00-1C-FF-AB-9E-D4
 Malware  Any type of code or program that has a malicious purpose. Viruses, trojans, adware, etc
 Megabyte  One million bytes
 Modem  Modulator Demodulator. Converts an analog signal to a digital one and vice versa
 Motherboard  The main board that the CPU, all peripheral cards etc. are attached or plugged into. Also known colloquially as mobo.
 Mouse  Device connected to the keyboard that allows a user to move a cursor (pointer) around the screen and select an object of interest
 NAS  Network Attached Storage. A device that connects to the network and contains multiple disks in a RAID configuration, which is shareable to other devices on the network
 Network  Two or more computers connected together, directly via a cable or wirelessly. Wired cables usually run over Ethernet and commonly connect to a router or a switch
 Network Card (NIC)  An add-on card that allows a network connection to the computer. These days, this functionality is usually built into the motherboard. For consumer use, the standard is now 1 Gigabit
 Ohms  The unit of measurement of resistance with the symbol Ω
 Operating System  Software that allows a user to interact with the computer in a user-friendly method. Windows, Linux, Mac-OS, etc. are examples of operating systems
 Parallel Port  Superseded by USB. This was a now obsolete method for connecting peripheral devices, usually a printer, to the computer
 PCI Bus  Peripheral Component Interconnect. The current computer bus standard. PCI Express, or PCIe is a high speed variant used to attach graphics cards or SSD cards to the motherboard
 Phishing  Pronounced fishing. An attempt to acquire sensitive information such as usernames, passwords, and credit card details (and sometimes, indirectly, money) by masquerading as a trustworthy entity in an electronic communication.
 Ping  As the name might suggest, it is a command used to troubleshoot the status of a network device to see if it is on or not and the speed of the network link to it, in a similar way a submarine might use its sonar equipment to detect another submarine or ship
 POP3  Post Office Protocol 3. A protocol used by email systems to download mail from a server. POP3 typically deletes email from the server once it has been downloaded
 Power Supply (PSU)  This is a transformer which converts 240V AC into 12V DC, 5V DC and 3.3V DC depending on what type of device it is supplying power to
 PS/2  Mini-DIN plug for connecting a mouse (green) and keyboard (purple) to the motherboard. Its name comes from the original IBM PS/2 computer. Superseded by USB
 RAID  Redundant Array of Inexpensive (Independent) Disks. A configuration of hard drives working together as a unit that provides a large block of disk space and in all cases greater than level 0, fault tolerance and redundancy. This means that if one (or more) of the disks fails, then it (they) can be replaced without downtime (if the disks are hot-swappable) or data loss. It is prudent to use the same type and size of disk in the array, as the total size is based on the smallest disk and any leftover space on bigger drives cannot be used in the array. Typical configurations are:

RAID 0:  Disk striping. Data is striped across all disks in the array, which is the total size of all the disks together. Very fast read/write speeds but no fault tolerance or redundancy. If any drive in the array fails, the data is lost.

RAID 1:  Disk mirroring. Data is written simultaneously to both disks so each disk is a mirror copy of the other. If one fails, the mirror can be broken, the drive replaced and the array rebuilt automatically with no data loss. The system can function on one drive until the other is replaced.

RAID 5:  Disk striping with parity, the most commonly used configuration. This requires a minimum of 3 disks with one drive devoted to parity (checking information). This means that the total size of the array is the disk size multiplied by the number of disks minus one, i.e. size(n-1). If any one disk fails, it can be replaced with no loss of data.

RAID 6:  Like RAID 5 except two disks are devoted for parity. Safer for configurations with a large number of disks in that if up to two disks fail at once, the data is not lost.

RAID 10: RAID 1+0. A Combination of RAID 1 and RAID 0, disk mirroring with striping. Requires a minimum of 4 disks and is the best option (and most expensive) for mission critical systems and databases.
 RAM  Random Access Memory. this memory is very fast but volatile in that it loses the data stored when the power is switched off. All computer instructions are processed here
 Resistance  The resistance of electric current flow, represented by the symbol R. Ohms Law, one of the basic laws of electronics states that V=IR, where voltage=current x resistance in an electronic circuit
 Resistor  A device that is used to restrict or lessen the flow of current in an electronic circuit. A variable resistor, or rheostat can be used to control the flow of current, like a light dimmer switch for example
 ROM  Read Only Memory. Memory that is not designed to be changed, that has a specific task. Computer firmware, used to drive or control a device, such as on a hard drive, resides in ROM. It can be updated but requires a special program or procedure to do it
 Router  Pronounced the same as “outer” here in Australia ;). This device connects other devices on the same network and is often incorporated with a modem to connect to the Internet
 SATA  Serial Advanced Technology Attachment. The current standard for attaching disk drives to a system. Variants include eSATA (external) and mSATA (mini). This type of connector is hot-swappable, meaning that devices can be connected while the computer is powered on
 Serial (COM) Port  Connector port on IBM compatible PCs but very rarely used today, except for things like barcode scanners and connectors to various devices to update their firmware
 SMTP  Simple Mail Transfer Protocol. A protocol used to send email from an email client and to send and receive (or relay) messages between servers
 Software  A computer program that performs a function or set of functions. Examples are Microsoft Word, Google Chrome, Angry Birds and many others too numerous to mention
 SSD  Solid State Drive. This type of fixed drive has no moving parts, therefore it is MUCH faster, smaller and lighter than a traditional hard disk drive
 TCP/IP  Transmission Control Protocol / Internet Protocol. The language of networking
 Terabytes  One thousand Gigabytes (One trillion bytes)
 Transistor  A device that can be used as an electronically controlled amplifier or switch. The building blocks of integrated circuits and computers and found in pretty much everything electronic we use today
 Trojan  A malicious program masquerading as a legitimate piece of software
 Upload  The process of copying a local file to a remote destination
 UPS  Uninterruptable Power Supply. A device which can provide power to sensitive electronic equipment, giving it surge protection and battery backup. A management interface can be connected to it via USB to provide facilities like automatic (graceful) shutdown in the case of power failure. The device will switch to battery power in the event of a power failure, protecting the device from damage or data loss
 USB  Universal Serial Bus. The current industry standard for connecting devices to a computer, be they cameras, mobile phones, printers, etc.
 VGA  Video Graphics Array. Analog video using 15 pin male and female connectors. Usually recognisable with a blue coloured connector
 Virus  In computer terms, code that is designed for a malicious purpose to cause harm to an infected system
 Voltage  The potential difference between two points in an electronic circuit
 Volts  Unit of measurement of Potential Difference with the symbol V
 WAN  Wide Area Network. Devices linked that are not in the same physical location, for example different offices of the same company located in different cities
 Watts  Unit of measurement of Power with the symbol W. A typical PSU might be 500W which is enough for most needs but higher end users with large numbers of HDDs and/or a higher-end graphics card will usually require a more powerful power supply