Some would have you believe, it seems, that the PDA (personal digital assistant) has peaked, and that its days are numbered. Don't you believe a word. For just as in most other walks of the IT world, the technology is getting better and the prices are getting smaller. And that's got to be a very good thing. As usual, though, there are a few things to be wary of before plumping for a PDA, and that goes for Smart phones too. So without further ado...

The obvious place to start is with the display. The screen is vital on a PDA, not just for viewing, but also in some cases for interaction. Depending on your budget, you have a fair few choices, too. At the very low end, for instance, you can opt for a screen that's monochrome. That'll be fine if you're just doing some basic personal organisation, but the price differential between mono and colour isn't that much of an obstacle now, although naturally the latter will drain your batteries quicker (and that needs to be a major consideration).

You should also take note of the resolutions offered. If you're au fait with desktop PC specs, the principles are similar - the higher the resolution, the sharper the image quality is going to be. Resolutions can go anywhere from 240 x 320 pixels right up to 800 x 600. It pays, at the very least, to opt for something around the middle of those two.

Now the OS. Here's an area of computing where Microsoft doesn't have things all its own way. In the PDA market, you have a choice of operating systems, although inevitably you'll end up with the one that comes bundled with the machine you ultimately opt to buy.

Starting with Windows Mobile OS, which as you'd expect bears quite a resemblance in terms of the way it works to its desktop counterpart. Whilst it's a more memory hungry operating system, it does offer pocket versions of popular Microsoft applications, including Outlook, Media Player, Word and MSN Messenger. It's easy to use, and if you're a fan of the Windows XP way of working, you're unlikely to find it too troublesome. It doesn't like talking to Apple Macs, though.

So spare a moment for Palm OS. Renowned for not unnecessarily overcomplicating things and for running quickly, it happily works with both PCs and Macs (primarily through a Palm Desktop application), and remains the most popular PDA operating system. It's generally accepted that - at the time of writing - it's the simpler of the two main PDA OSs, although that gap continues to narrow.

For Smart phones there are other options too. Symbian OS is a powerful, flexible contender, particularly for business-oriented phone/PDAs, while Linux has appeared on a couple of PDAs, without much take-up at the time of writing.

An extremely important factor, that can make a hefty difference to the performance of your PDA, is memory. To put things into context, if you run Microsoft's Windows Mobile OS, then you'll be needing at least 64MB of internal memory, but it won't hurt to get more. The PalmOS is far less demanding, with 16MB ample to get the OS up and running.

Generally, as PDAs generally come loaded with a good software package, you'll more often than not find that the included memory is ample to run everything you get with your purchase, and that it's third party software and multimedia content that pushes memory demands up. Suffice to say, the more internal memory you're after, the higher the price (although it may be worth checking if your PDA's memory is upgradeable, and if those upgrades are affordable).

You should also consider external memory support. The modern PDA supports a flash memory card (and it's worth checking that the model you're interested in is expandable in this way), with Compact Flash (CF) and Secure Digital (SD) flash cards the most popular. Such expansions are not only a useful way of transferring data, but they can also help cater for content (particularly music and video) and programs with higher memory demands. The fall in price of flash memory cards makes such expansions even more appealing.

The majority of contemporary PDAs have some sort of wireless functionality built in, and for communication purposes this can be a very good thing. Still the most popular is infra-red, and this allows the PDA to easily transfer data across to another device with such a port. The downside to infra-red of course is that the range is limited, and both sender and receiver need to be able to see each other, with no physical obstructions in the way.

Wi-Fi is growing in popularity, not least because it's a technology that also supports Web access. It can still communicate with other machines, but if you're in the vicinity of a Wi-Fi hotspot, you can also get online with ease. Don't forget Bluetooth either. The range may be limited, but because you can specify which devices can talk to each other - for instance, your laptop and your PDA - it can be a straightforward way to get wireless communication working. It's not as fast as Wi-Fi, goes quicker than infra-red and has a variety of uses. Many PDAs now combine both Bluetooth and Wi-Fi in the same device, so at least you have the choice.

Some PDAs and a few phones have keyboards built-in, others relying on you interfacing with the device through the screen itself and a stylus pen. Almost every dedicated PDA will support a stylus, and will have built into it handwriting recognition software and an on-screen keyboard (the Windows OS does this slightly better than its Palm counterpart), but a physical keyboard can be a lot less fiddly. Again, the added feature of a keyboard will up the price, and for those with large fingers, it might not be much use anyway.

Turning to battery life, you should on the whole get around three to four hours of continuous use out of a single charge of your dedicated PDA's batteries (assuming they're rechargeable). This is an area where inroads are slowly being made, but power consumption depends very much on what you're using the device for. A continuous video with accompanying music will eat batteries quicker than a bit of mailing and writing, as you'd expect.

These are the fundamental basics you need to consider when buying a PDA, and pretty much account - along with processor speed - for the price differentials. You'll find that all PDAs have software that allows you to sychronise your machine with a computer, although Mac users may need third party software if they buy a Windows-based machine.

Units start from under £70 and go up to well over £300, sometimes even more than that if you want a Smart phone that's not tied to a particular contract. However, always consider what you actually want to use the device for. If it's a simple communication and mobile working tool you're after, then a modest unit will suffice.

If you don't want to carry around both a mobile phone and a PDA, you should probably opt for a Smart phone, which is a hybrid of both devices. They tend to offer a broad range of features on top, too, including entertainment facilities and music playback, and some include a basic digital camera (although if you're ever used a camera-phone you'll pretty much know what to expect).

They're not cheap devices, but the price of Smart phones does continue to fall. If you are looking to go down this route, be wary that you're not suckered by irrelevant features, and again make sure you get a device that does what you need it to, rather than something that looks nice in a brochure.