Glossary of IT Terms

The glossary is not intended to cover every aspect of the I.T. world. While we try very hard to avoid the use of jargon in our conversations, our customers will inevitably come across technical terms and ask for an explanation. These are the most common ones.

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CPU is an abbreviation for central processing unit but most people call it simply the “processor”. It’s a chip inside a computer often described as the brain of the system. It processes all the information that is going in and out of the system and between all the components inside of the computer and sends the information to where it’s supposed to go. A CPU functions like a very powerful calculator, it can add, subtract, multiply, divide and move billions of numbers per second. That speed enables computers to perform tasks such as accessing the internet, playing video games and creating graphics.


Cloud computing gets its name from the way the internet or other networks are traditionally drawn on a diagram as a cloud. The term “cloud” in I.T. terms is used to cover a wide variety of services. One cloud service is not necessarily the same as another.

The “cloud” is essentially something on the other end of your internet connection (or maybe your private network connection), which provides some kind of computing-related service.

Examples could be an offsite file backup service, a hosted telephone system, a file server or even your Windows desktop.


DSL or Digital Subscriber Line is a type of internet connection. The most well known one is ADSL, also known as broadband. ADSL is Asymmetric Digital Subscriber Line and indicates that the download speed is different to the upload speed. This is the type most prevalent in homes and small business as it is optimized for web browsing and downloading files, where most of the data traffic is being transferred into the office or home, not out.

The other version is Symmetric Digital Subscriber Line or SDSL, where traffic can flow at the same speed in both directions. This is more suitable for voice traffic (Voice over IP) where the same amount of traffic flows in both directions.


When connecting to a computer or web site we usually use a host name such as The name “” is known as a domain and DNS, or domain name system, is used to translate that name to an IP address. It is an IP address which is used to ensure that information goes down the right connection to reach its destination. We humans would find it very tedious to remember IP addresses so we leave DNS to do all this translation. DNS is a distributed database, in other words, like a phone book split up into small sections. If your computer asks your usual DNS server to lookup an IP address and it does not know the answer, it will know the name of another DNS server that it can ask. Sometimes if you have a connection to the internet but cannot access a website, it is because of a fault with DNS.


EFM (Ethernet in the First Mile) provides high speed, reliable internet connections for businesses that require more than traditional broadband can offer.


FTTC stands for Fibre to the Cabinet. It’s a term for broadband network architecture where copper cables going from the local telephone exchange to the street cabinet are replaced by fibre optic cable. The connection between the building and street cabinet (approx. 300m) is provided by using existing copper telephone cables. This architecture allows for use of existing infrastructure in the buildings which lowers the cost of deploying it while significantly improving speed of internet connection.


This is an acronym for Generic Ethernet Access and provides a similar, but cheaper service that EFM (see above). It depends on the FTTC (see above) service being provided to your local street telephone cabinet.

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Hard drive

A hard drive is a mass storage device where a computer stores, saves and retrieves data from. It’s like a big virtual room with lots of filing cabinets where you can store your files and documents. There are currently two major technologies of hard drive, HDD and SSD. First is a traditional hard disk drive (HDD), composed of individual disks, or platters, with read/write heads contained in a sealed case. Second is the solid-state drive (SSD) which compared to HDD has no moving parts: it’s basically a huge memory card that is used in many well-known devices like cameras. Both technologies have their strengths and weaknesses. SSD is much faster but it has a limit of how many times information can be written and it’s expensive; HDD is cheaper and doesn’t have that limit but because of having moving parts inside it is more likely to fail.

IP address

An IP (Internet Protocol) address is a unique identification number for systems on a network. If anyone wants to connect to a server or web site we need to know the address of it. For every person the easiest way of remembering that address is using words but in an IP network systems don’t have names but use IP addresses. There is a great real live analogy we can use to help understand it: an IP address is like a phone number. If you want to call somebody you need to know his phone number – we have the same situation computers. If one computer needs to contact another it needs to know the other computer’s IP address. The IP address consist of four sets of eight binary numbers (zeros and ones), each separated by a period (or full stop) but to make it easier to users we use the decimal equivalent. So instead a lot of 0s and 1s separated by dots we get four sets of numbers (still separated by dots) from 0 to 255 which greatly help to use and memorize it. An example might be If you want to connect to a website, the web address will be translated for your computer to an IP address first using something called DNS (domain name system).


ISDN or Integrated Services Digital Network is a type of telephone connection which can be used for voice and data. In the 1990s it was very commonly used for data but that function has mostly been replaced by alternatives such as broadband (ADSL, SDSL). It is still in very wide use for carrying telephone calls as it provides better quality and reliability, plus more functionality that a standard analogue line. Most businesses requiring more than one simultaneous telephone call will use ISDN lines, rather than multiple analogue lines. The more recent alternative which is now replacing ISDN are SIP trunks.


An Internet Services Provider provides residential and business users with a connection to the internet.

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RAM is an acronym for random access memory and is a form of computer data storage. It’s a chip or chips used by a computer to store information currently used by the operating system (such as Microsoft Windows, or Apple OSX) and currently working programs. When not in use, all programs and data are held on mass storage devices like hard drives. RAM because of its speed helps to prevent slowdowns when moving information from hard drive to CPU. When an application is being used all required information is loaded to RAM which makes it quickly accessible. A good real live analogy would be working on a project, where you take all relevant documents from a filing cabinet in the next room (hard drive) and put them on your desk (RAM). So basically you can save the time of getting a file or document from room next door every time you need it. It makes work more efficient and quicker just like RAM makes work more efficient and quicker for the CPU.


This is a hardware device which directs or routes data from one network to another. It often incorporates a device (an ADSL modem) which allows connection to the internet via a telephone socket. Often when your internet connection fails, you will be asked to restart your router.


SDSL is an abbreviation for Symmetric Digital Subscriber Line. It’s an internet connection service commonly known as broadband where the upload and download speed is the same. It is mainly used in small and medium professional environments where having high speed of upload data is essential (backup of data, videoconference). It cannot co-exist with conventional voice (telephone) service on the same cable as it uses the entire bandwidth. It is considered the opposite of ADSL used almost exclusively in non-professional applications (home internet) where download of data it significantly faster than upload.


A server is a computer system designed to provide shared resources to users connected via a network. There are many types, some with a single purpose, others providing multiple functions. A website is provided by a web server. A file server, the most common type found in offices environments, allows users to share access to the same files. Other examples include printer servers and database servers.

While technically many computers including even a Windows XP based laptop can function as a server, it is more common to use a computer which has been built from hardware and software specifically designed for a server role. Since a server is used by many users simultaneously its design parameters are focused on performance, reliability and manageability.

SIP trunks

SIP trunks are taking over from ISDN. (SIP is an acronym for Session Initiation Protocol, but there is no need to understand it – just think of it as a different way of connecting telephone calls). SIP trunks provide the same call quality as ISDN but at a much reduced price. An additional benefit is that numbers from any area code can be applied to your SIP trunks. You could have an office in Portsmouth, but advertise both Portsmouth and Southampton phone lines. This also means that if you ever relocate, you can take your number with you.


Software that collects private information or monitors user behaviour secretly. The term ‘spyware’ essentially covers any software that gathers information and passes it to a third party without adequate permission from the owner of the data.


A Service Set Identifier is used to identify and distinguish a wireless network. When scanning for a wireless network to join, the displayed list of available networks is a list of SSIDs.

System unit

This is the box that contains your desktop computer. Usually it will be connected to a screen, keyboard and mouse. In some cases it is combined with the screen – known as an “All-In-One”. The system unit contains the RAM, hard drive and other essential hardware components. If an I.T. support technician asks you to switch off your computer, it is the system unit to which they will be referring.

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A Trojan (or Trojan horse) is a malicious program masquerading as something innocuous or even useful. Trojans use social engineering to convince victims to execute their code, and often act in a clandestine manner, sometimes even providing the useful functionality promised while running malicious actions in secret.

The great majority of malware takes the form of Trojans – software such as adware and spyware also falls into this category, as actions which are not revealed during the installation process are carried out in a clandestine manner once installed. Trojan infections can come from malicious or hijacked websites, either using social engineering to persuade victims to install the file or exploiting vulnerabilities to carry out silent drive-by downloads. Trojans may also be sent out via email spam, with the email either including an attachment (the Trojan file itself), or including links to the malicious or hijacked sites mentioned previously, again using social engineering to persuade readers to visit the site. Trojans can also be spread via other communication methods such as Instant Messaging or Peer to Peer file sharing, or even dropped by self-replicating malware.

Many Trojan infestations involve a variety of files, each providing different functionality. Typical types of Trojan include downloaders, keyloggers, backdoors, clickers and diallers.


This is an uninterruptible power supply. It contains a standby battery which automatically cuts in when mains power fails. It is highly recommended for supplying power to servers and other critical equipment or for all computer systems in an area with unreliable mains power.


The term ‘computer virus’ is often used as a general term for all types of malware, including Trojans and other non-replicating malicious code. In a stricter sense ‘virus’ applies only to self-replicating malware, and even more specifically only to code which infects other files on the local system (rather than spreading from one system to another in the form of an unchanging file, as is the case with most worms).


Voice over IP refers to the technique of carrying telephone calls over the internet. It is a low cost alternative to traditional telephone systems.


This is a Virtual Private Network and refers to the technique of using standard internet connections such as broadband to connect multiple locations together in a secure manner. An alternative is to use private leased lines, but this is far more expensive.


Worms are a form of self-replicating malware which spread by placing copies of themselves in email attachments or instant messages, in shared folders or on visible network shares, or via backdoors or vulnerabilities in network-exposed software. As well as spreading, and using up valuable bandwidth in the process, worms often open further backdoors, disable security software and install “bot” software to add infected systems to zombie networks.

Worms have caused many of the biggest and highest-profile outbreaks in the history of malicious code, including the infamous Melissa and Loveletter incidents in the 1990s and SQL/Slammer in 2003.

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