ADSL (Asymmetric Digital Subscriber Line) is a technology for transmitting digital (data) information at a high speed on existing phone lines to homes and businesses. Asymmetric means simply that the �send� speed and �receive� speed are different.

Unlike regular dialup phone service, ADSL provides continuously-available, "always on" connection. ADSL simultaneously accommodates data and voice information on the same line � so you can make phone calls at the same time as use the internet!

Here is a diagram of all the bits involved in getting ADSL to work, and let�s take a look at each in turn.

1. Your PC. You are familiar with this of course! It�s where you communicate with the internet, as well as lots of other things!

2. Your MODEM/Router. This acts similar to a network card and allows your PC to �speak� to the Internet using ADSL. It controls the actual sending and receiving of data. The difference between a modem and a router is simply that a router can share the ADSL connection with more than one PC, and is always �on�. Wireless modems are becoming increasingly popular for use here, providing greater flexibility. Note that even desktops can be fitted with w-lan cards!

3. The micro-filter/splitter. The main reason for this is to stop the ADSL signal interfering with the voice part of your phone line - this sounds a bit like 'fast clicks' when it happens. The microfilter is usually plugged into a �splitter� which is a simple adapter that plugs into your phone wall socket. Then you can plug both your microfilter and phone into the one phone socket. The microfilter/splitter are what splits out the data for your PC and the voice signal for your phone.

4. Your combined voice and data signal is then sent down the telephone line which connected to your local TELEPHONE EXCHANGE. Once there, the ADSL and voice components of the signal are split apart in the same way as your splitter works at home or in the office.

5. The HOME GATEWAY takes the data you have sent across the telephone line and converts and then sends it to your ISP (Internet Service Provider, such as� CAT, TOT or TT&T). Your ISP provides access to the rest of the internet for you.

So all the data you send from your PC goes through the above process even BEFORE it gets to the internet for real, and similarly the process is reversed for all data that is sent back to your PC.

ADSL was designed for the one-way nature of most internet communications, in which large amounts of information flow toward the user and only a small amount of information is sent by the user. Several experiments with ADSL to real users began in 1996, and in 1998, wide-scale installations began in several parts of the U.S. ADSL is now readily available here in Thailand, and can usually be installed with 10 working days. CAT and TTT offer a 4 MIP/1MIP service, the fastest available around here at the moment but the difference with CAT ADSL is that they run a dedicated line to your property that is for data transfer only, and cannot be used for phone calls.

So, this has been a very simple introduction to ADSL, but as one of the most frequent questions we get is �Why is my ADSL not working� you may now appreciate why it�s not always possible to give an instant answer! As to which is the best ADSL provider to use � well deals change almost every day. My best advice is to shop around!

Next this week a reminder on basic hard drive maintenance.

If you think about the way you use your PC, you add files to it, change other files and delete yet others. Most of this activity centers around your hard disk, which basically gets �untidy�. From time to time, you need to do a bit of �spring cleaning