A modem is a device that sits between your computer and the phone line, turning information stored in digital form (a stream of digital ones and zeroes) in your computer, into an analogue form (a continuously varying wave form) currently used on our residential phone lines. At the other end of the connection, there'll be another modem which reconverts the analogue information back into digital form for the remote computer.

The name 'modem' comes from 'modulate/demodulate', describing how it modulates the digital information into analogue form and demodulates it again at the other end.

Speed
With modems, speed is everything. Nothing less than 33,600 bits per second (bps) will do. This is usually abbreviated to 33.6Kbps (kilobits per second). You'll also find 56Kbps modems, which theoretically provide 56Kbps speeds from the Internet to your computer (downloading), and 33.6Kbps from your computer to the Internet or another computer (uploading). In reality, 56K modems achieve download speeds of around 45 to 50Kbps -- but this is still a significant improvement over 33.6Kbps. There is a complication, however. There are two competing and incompatible 56Kbps technologies, X2 and K56flex, as well as a new official standard, V.90. Regardless of this, it's still well worth buying a 56Kbps modem -- if you're careful and follow these rules:

• Make sure your Internet service provider (or the one you plan to use) supports the same technology as your modem -- either X2 or K56flex. Fortunately, most major ISPs support both -- but check first!
• Internet service providers will move to the official standard soon after V.90 modems appear on the market in numbers -- so make sure your modem can be easily (and cheaply) upgraded to the V.90 standard. Better-quality modems make this an free, software-only upgrade that you can easily do yourself -- but again, check this out carefully.
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Fax capabilities
Do you want a fax-modem, or will a straight modem without fax capabilities do? This used to be a big issue, but these days you'll find most modems have built-in fax capabilities, so you may as well just go with the flow even if you're not into faxing.

Internal or external
The modem can be an internal model, fitting into an expansion slot on the motherboard inside your computer, or an external model that sits in its own little box beside the computer. External modems usually cost a little more, but have the advantage of being portable, and of providing visual and sometimes aural feedback on the progress of your modem connections.

Software
You'll also need communications software to run your modem. Windows 95 comes with some quite good communications and fax software, including the core software to allow your PC to get onto the Internet. However, you may want to add other Internet software (see 'Introducing the Internet' in the PC & Internet Starter Kit) and more powerful communications software such as WinFax Pro, which comes with sophisticated fax and answering-machine (or 'voice mail') features.