Asus's eee PC weighs less than a kilo.

What is it? As the name suggests, an ultra-mobile personal computer – or UMPC for short – is an itty-bitty notebook computer. The term UMPC originally referred to a specific Microsoft project back in 2006, but has now become the generic name for a particular category of pint-sized mobile computer.

Why would I want one? Aside from UMPCs, you have two main options for mobile computing, both with their advantages and disadvantages.

First, there is the personal digital assistant (PDA) or smartphone – for example, a Blackberry. It’s small enough to fit in the palm of your hand, and you can easily use it to access the Internet and send/receive emails. However, the small size can also be its downfall. Many people find it too fiddly to use such a compact device for anything more than on-the-run email.

At the other end of the mobile-computing spectrum is a regular notebook PC. Unlike a PDA, this is powerful enough to run full-strength versions of common operating systems (such as Windows XP or Vista) and business software (such as Word and Excel). It also has a comparatively large screen and keyboard, which make it more practical for day-to-day work. However, while they are obviously smaller than a desktop PC, standard notebooks can still weigh up to three kilos. Imagine that weight in sausages, and then imagine carrying it around all day.

UMPCs are intended to be a happy new medium between a PDA and a notebook. They are still small enough to slip into your handbag, but they also have a decent size screen and keyboard, and can run the software you need.

HP's Mini-Note will be available in Australia from next month for an RRP of $899.

Who makes them? Only a few computer suppliers have ventured into this category so far. Most notable is Asus, which at the end of 2007 released the eee PC – and promptly sold out of its first shipment. Last week, Hewlett-Packard (HP) announced that the HP 2133 Mini-Note will be available from May. We predict more companies will jump on the UMPC bandwagon this year, so watch this space.

How small are we talking? The Mini-Note starts at around 1.19 kilos, and its dimensions are 27 millimetres high (at the front) by 255 millimetres wide and 165 millimetres deep. The eee PC is smaller still. It weighs just 0.92 kilos, and is about 20 millimetres high at the front, 225 millimetres wide, and 160 millimetres deep. If you’re having trouble conceptualising that, picture a new release hard-cover novel and you’ll be in the same ball park.

Sounds great! There must be a downside. Isn’t there always? The main gripe among UMPC users is about battery life. HP’s Mini-Note comes as standard with a three-cell battery that lasts only two hours and 15 minutes before it needs re-charging. You’ll get around three hours out of the eee PC’s four-cell battery. You can opt for a bigger battery, but you’ll pay more for this privilege, and you still won’t have enough juice for a full eight-hour work day.

Also, neither the Mini-Note nor the eee PC has a CD or DVD drive. If you’re likely to need one, you can buy an external DVD drive – but this will set you back about $150, and then you’ll have to carry it around with you.

In addition, if you opt for the eee PC, it comes with an operating system called Linux (instead of a Windows operating system). While this keeps the price down, it could take you a while to adjust if you have only ever used Windows. There are instructions in the manual for loading Windows XP, but in order to do this, you’ll need a copy of XP and the external DVD drive – and a high degree of technical confidence!

What do they cost? The eee PC starts at around $499, while HP told ConnectedWomen that the Mini-Note will retail for around $899 with Windows Vista installed. We expect that any UMPC newcomers will be similarly priced to the HP offering.