Once a rich man's play thing, the PDA – Personal Digital Assistant – has finally become just another business essential and at a price that everyone can afford. Keeping customer details on your computer makes producing invoices and sending marketing promotions simple, but how do you take those details with you when you're out and about visiting customers or suppliers? If you're always making to-do lists or jotting down ideas on scraps of paper that you always lose, a pocket computer – usually called a personal digital assistant – could be just what you want. You can take your diary and address book with you, make a to-do list, jot down notes, keep track of expenses, read and reply to your email and even browse the web. If you need to, you can even get some work done using word processing, database and spreadsheet software that comes as standard with most PDAs. There is a wide range available from simple electronic organisers to miniature notebook PCs. Basic organisers are cheaper but you can't expand them by adding new programs or extra features. You get better value from handheld and palmtop computers that let you install new software or plug in more storage, or even extra devices like digital cameras and global positioning systems (GPS) so you know exactly where you are and how to get to your next appointment. There's something to cover most needs, so all that you need to do is decide what format is right for you. Pocket or Palm. The point of a PDA is that it's small and light so you can carry it around in your pocket or your bag. Some PDAs are very thin and most are light – between 142 grams (5oz) and 284 grams (10oz). But there's quite a difference between the lightest, thinnest PDAs and the larger, heavier models. That's usually down to the size of the screen and whether you get a keyboard to type on or a touch screen that you can write on with a stylus. If you want your PDA to do more than it does the day you buy it, look at expansion options. Nearly every PDA on the market lets you add extra memory or other gadgets – and nearly every PDA does it differently. You control palmtops by pressing buttons on the case or tapping the screen with the stylus. To write with the stylus you can tap out the letters on an on-screen keyboard, employ handwriting recognition that will understand most of your writing or learn special abbreviations for letters (called Graffiti).

PDAs running Palm OS have a small area at the bottom of the screen just for writing Graffiti; with Pocket PCs you can write anywhere on the screen and when you're not writing you can use the whole screen.

If you want to use a keyboard with a palmtop, you can get folding ones that open out to give you keys almost the same size as on a standard computer keyboard. You have to plug these into the connector at the bottom of your PDA and you need to be sitting at a table to use them, but they're light to carry and much faster than writing or tapping on the screen.

Weight & Size
Most PDAs are very light and fit into a bag or a pocket and manufacturers are making them thinner and lighter all the time. You have to carry this around all day so make sure it will not weigh you down.

With new features coming out all the time the price of new models can seem high in comparison to older stock, but what can they really do and do you understand all the terms that the salesman is talking about? Read our glossary below to understand all the jargon.