Instant messaging (IM)

Screenshot of ICQ2Go, a web-based instant messaging service that doesn’t require the software to be downloaded and installed before use.

Instant messaging is a tool for allowing two or more people to communicate instantly via text messages over the internet.

Email can appear to be instant. However, it can take minutes, hours or even days for them to be delivered. SMS messages on mobile phones can also take hours or days to arrive.

Instant messaging systems are different. They are designed to make what you type into your computer appear on the screen of another person as soon as you finish typing it.

Modern instant messaging systems have been around since 1996, when ICQ was released. Since then a number of competing systems have been launched. In most cases these were incompatible with each other, making it difficult and often impossible to instant message people on other systems.

The different instant messaging companies are now working towards allowing people on any system to send messages to people on other systems. A few systems already exist that allow this, such as Trillian .

The most popular systems are all free to use and include AOL Instant Messenger , Yahoo Messenger , Microsoft Messenger and ICQ .

Instant messaging systems are beginning to outgrow their original focus on sending text messages via computers. Many have introduced features such as conferences (like IRC channels), voice messaging (like voice-over-IP telephony) and photo sharing. Some allow mobile phones to send and receive instant messages to other phones and computers.

How instant messaging systems work

Instant messaging systems rely on two pieces of software to work.

A central server is used to manage messages from the different people using the system.

Users need to install a piece of software (usually free) known as a ‘client’. This client software allows their computer or mobile phone to connect to the central server and provides the tools needed to send and receive messages.

Each user, when installing the client software, must select a unique username – like a phone number – that identifies them on the system. This is used by the central server to make sure messages are sent to the right person.

Sending and receiving messages

To send a message, you must know the username of the person you wish to message. Often friends tell each other their usernames, some instant messaging services also have a directory listing users by location and interests.

Once the username is known, you can either type it into the client or select it from a list of contacts set up in the software. You then type your message and press ‘send’. The recipient will receive a notification via a flashing button or sound that the message has arrived. They can then choose to read and respond to the message.

People often have phones or computers on but are doing other things most instant messaging systems allow them to set whether they are available to receive messages or are busy. Some also allow people to filter who is allowed to send them messages, so they can only receive them from friends or even only selected friends.