Network hardware: Gateway to the Net

Steve Homer begins our hardware special with a look at everything you need to know about modems

What is a modem?

It's a box that lets your computer talk to another computer over the phone line.

But can't you just plug the computer into the phone socket? I have seen computers like that.

No. Those computers have a modem built inside them. The computer and the telephone system talk in a different way. The telephone is designed to transmit voice; so to make your computer talk over the telephone system you have to give it a "voice". If you listen carefully it is a bit like someone talking very fast.

Is it better to have your modem inside or outside your computer?

An internal modem is neater. You have fewer cables around your computer, and they are less easy to steal. But external modems are more flexible. You can buy a better one if you need to upgrade, and if you want to lend it to someone or share it around the office you can do that more easily. Also most people don't like opening up their computer to put things inside.

So as faster external modems come along you can just plug them in to the back of your PC? If you have a modern PC, yes. But some older PCs do not have a fast enough "serial port" - the socket on the back where the modem connects. You can get round this by buying a new port.

What speeds do modems work at?

Nearly all modems today operate at V34 or V.32bis ...

Sorry?

That is industry jargon for 28.8 and 14.4 modems.

What does that mean?

A 28.8 modem sends data at 28,800 bits per second. What that means is that it will send around 3,600 characters or around 600 words per second.

Do I necessarily need a modem this fast?

Well, if you send or receive a good deal of data, it will save on the phone bill. And if you want to look at the World Wide Web or other graphical material, you should definitely go for the fastest modem you can. But if you just want to send text or e-mail, 14.4 or even slower will do the trick.

Can I use a modem with a mobile computer?

You can plug an external modem into the back of a portable, or you can buy a tiny "PC Card" modem that slots into a modern laptop or notebook computer.

No, I meant can I use a modem on the move with a portable computer?

Oh with a mobile phone? Yes you can but it will not be as fast. If you plug your portable computer into the wall you will be able to get the same speeds as a desktop machine. Over a mobile phone the best you will manage is 9,600 bps, and then only when you use a digital phone.

What do you mean?

With some digital phones, notably all the Nokia ones, you can send data at 9.6. But many phones, even some quite modern ones, will only operate at 2,400 bits per second. To have a full "mobile office", you should get the right phone with a plug-in "data card", which is not quite the same as a modem - and is a lot more expensive. For the older analogue phones the best you will normally ever get is 4,800 and that is stationary with a very good signal.

How fast will modems go - eventually?

The industry has nearly agreed on a new standard for modems running at 33,600 bits per second. After that it does not look like things will get any faster. Maybe a little but not much.

What do you mean, not this year?

No, never. It has to do with the characteristics of telephone lines, which are agreed by the operators. The main problem is noise on the line - the crackle in the background as it were. Under current agreements the speed limit is probably around 40,000 bits per second. You can get faster access by switching to an ISDN line, but this has to be installed specially (see ISDN article below).

How much do modems cost?

Typically a 28.8 modem will set you back around pounds 180 and a 14.4 modem will cost around pounds 110 on the street or mail order. Don't forget that if you fork out for a 28.8 modem, you will not necessarily get access at that speed: the line works at the rate of the slowest modem in whatever chain you happen to be linked to. You can pay more, though, if you want extra functions.

Such as?

Well, some modems now have a "voice" function, which converts speech into a language computers understand - this means they can turn the computer into a sophisticated answerphone or voicemail system. Very handy if you want to kid people you are a giant corporation.

Thanks to US Robotics and Hayes for their help in preparing this article.