ICDL Computer & Online Essentials (ICDL) cheat sheet

Hardware is the physical equipment (processor, memory, screen, keyboard); software is the set of instructions (operating system, applications) that runs on that equipment.

Input devices convert user actions into data (keyboard, mouse, scanner, microphone); output devices present processed results (monitor, printer, speaker); a touchscreen performs both roles.

RAM is volatile working memory cleared when power is switched off; HDD and SSD storage is non-volatile and keeps files when the device is shut down.

The operating system manages hardware, runs applications, organises files and provides the user interface, for example Windows, macOS, Linux, Android or iOS.

File extensions select the application used to open a file: .docx word processing, .xlsx spreadsheet, .pptx presentation, .pdf fixed-layout document, .jpg/.png images, .mp3 audio, .mp4 video.

Standard shortcuts: Ctrl+C copy, Ctrl+X cut, Ctrl+V paste, Ctrl+Z undo, Ctrl+A select all, Ctrl+S save, Ctrl+P print.

Peripherals connect through USB, HDMI, Bluetooth or Wi-Fi; plug-and-play means the driver is installed automatically when the device is connected.

A backup makes a separate copy of data for recovery, whereas synchronisation mirrors changes so that both locations are updated to the same state.

Proprietary software requires a paid licence and forbids copying or modification; open-source software publishes its source code and may be used and modified under its licence terms.

A network is two or more devices connected so they can share data, files, printers and an internet connection.

A LAN covers a small area such as a home, office or school; a WAN spans large geographical distances by linking networks, and the internet is the largest WAN.

In a client-server network, central servers supply services and clients request them; in a peer-to-peer network, devices share resources directly with each other.

An IP address identifies a device on a network; DNS translates human-readable domain names such as example.com into the IP addresses used for routing.

A router forwards traffic between different networks, a switch connects devices inside a single LAN, and a modem converts the ISP signal for the local network.

Ethernet is a wired connection that is stable and fast but fixed in place; Wi-Fi is wireless, giving mobility but suffering from distance, walls and interference.

Bandwidth is the maximum data transfer rate in Mbps; latency is the delay in milliseconds. Downloads need high bandwidth, video calls need low latency.

HTTPS encrypts traffic between browser and website and is marked by a padlock; plain HTTP sends data unencrypted.

A URL takes the form protocol://domain-name/path, for example https://www.example.com/help.

To holds the primary recipients; Cc sends a visible copy to additional recipients; Bcc sends a copy whose addresses are hidden from all other recipients.

Reply answers only the original sender; Reply All answers the sender plus everyone in To and Cc; Forward sends the received message on to new recipients.

An email address has the form local-part@domain, for example [email protected], and cannot contain spaces.

Attachment size is capped by the provider, commonly around 20-25 MB in total; larger files are shared as a link to cloud storage instead.

Synchronous tools such as video calls, live chat and instant messaging require participants to be present at the same time; asynchronous tools such as email and forums do not.

Spam is unsolicited bulk email; phishing messages impersonate trusted senders and demand urgent action, so the sender address and links must be verified before responding.

Netiquette rules include avoiding ALL CAPS (read as shouting), writing descriptive subject lines, quoting only relevant text and not forwarding chain messages.

Cloud collaboration gives several users one shared document with permissions of view, comment or edit, and changes appear to all users in real time.

An out-of-office auto-reply answers incoming email automatically while the account owner is unavailable, stating when a reply can be expected.

A strong password is at least 12 characters long, mixes upper and lower case letters, digits and symbols, contains no dictionary words or personal data, and is unique to one account.

Two-factor authentication requires a second proof of identity, such as an SMS code, authenticator app or hardware key, in addition to the password.

Malware types: a virus attaches to files and spreads when they are opened; a worm self-replicates across networks; a trojan disguises itself as legitimate software; ransomware encrypts files and demands payment.

Phishing check: verify the sender address, hover over links to reveal the true URL, and never enter credentials on a page reached from an unsolicited message.

A firewall filters incoming and outgoing traffic against rules, while antivirus software detects and removes malware and must be kept updated with current definitions.

HTTPS and the padlock show that the connection is encrypted; they do not prove that the website owner is honest or that the site is trustworthy.

The 3-2-1 backup rule: keep three copies of data, on two different types of media, with one copy stored off-site.

Cookies are small files websites store in the browser for logins, preferences and tracking; they can be deleted or blocked in the browser settings.

Use only images, text and music that you own, that carry a licence such as Creative Commons, or that you have permission to use; copyright applies to online material as well.