Mobile devices

Which computer you choose will depend on what you want to do with it. If you need to use a computer that can do everything the computer on your desk (or under your table) can do, you need a desktop computer. These are very fast computers that can display videos, burn DVDs, and run the most modern versions of programs and operating systems. But size and strength means that these machines belong on a desk. It is hard to move them, and they run out of power very quickly unless they have a mains power supply.

PDAs are weakest in power and performance. But they are the marathon runners of the mobile world. They can run all day, and keep going long after the other two. You can carry them in a handbag or in a suit, so they can stay with you all day, and they have another advantage - they can turn on and off instantly. some people who work with computers can't decide which type of computers they need, so they have one of each!

There is an English proverb 'Horses for Courses'. This means that you should choose something suitable for the job you will be doing. Portable computers can weigh as much as six kilograms, or as little as 300 grams. They can run all the very latest programs, or they might be little more than an electronic diary and address book.

A portable laptop is a compromise. It tries to be as powerful as a desktop, or the desktop replacements we have just described and as light as a PDA, but it ends up as something in between. It is more powerful than a PDA, but less than a desktop replacement. It will run most programs, but do it more slowly. The screen is smaller, but the battery lasts longer, and so on. Portable laptops are not all alike - some are nearer to PDAs and others are almost desktop replacements.