9. Modem

A modem converts the digital data from the computer into a continuous analogue waveform that the telephone system is designed to deal with (This is the MODulation part of a modem). 

The reason for this is that the telephone system was originally designed for the human voice i.e. continuous signals.  The modem also converts the analogue signal *from* the telephone network back into digital data that the computer can understand. (DEModulation).

Hence the word MODEM (Short for MODulation and DEModulation)

Standard ADSL modems come in two forms. An external box that links to your computer through an USB port or a network cable (like the one above), or an internal modem that is plugged directly to the motherboard inside the computer.

Wi-Fi modems

In addition to telephone modems, radio has now become very popular as a means of connecting to the internet.

The device that allows you to do this is called the Wi-Fi modem.

Many domestic units combine a router, an ADSL modem and a wireless access point into one box, such as the one opposite. The front panel shows the 'DSL' light that comes on when a connection to the local telephone exchange is working, Another light on the panel called 'internet', lights up to show that the internet is being accessed over the DSL telephone line. A third light 'wireless' flickers off and on as someone connects by Wi-Fi. The two things sticking up in the background are the wi-fi antennas that pick up the wireless signals.

Looking around the back of the unit, you can see a number of network sockets

This one includes a router that allows up to four network connections to be made. These connections will allow four computers to share data irrespective of that telephone / internet connection. Alongside those network connections can be seen the telephone socket connector needed to connect to the internet. Along with the two wi-fi antennas for wireless connection..

3G Dongles

If you are on the move, another way to connect to the internet is by using a telecom dongle such as the ones below

These fit into an USB socket on your laptop and connect to a 3G mobile service - for example vodaphone and O2 dongles are shown above. This 3G connection will have a very slow speed compared to the normal Wi-Fi or network connection, so it is almost a 'last resort' for an internet connection.

The new 4G network promises more usual speeds. But 4G is yet to come to the UK in any force.

3G also has fairly small data bandwidth limits, so really,it is mainly useful for picking up email or viewing simple (low bandwidth web pages).