Note: if it is small, cheap and light - it is likely to be a netbook NOT a laptop and therefore not covered by these general requirements.

Laptops are usually banded by screen size - 10" to 17" across the diagonal of the screen. The typical laptop has 15.6" inches and usually is widescreen in a similar way to a television. Generally speaking smaller laptops with decent power/performance get more expensive with 12" being the peak of price and performance.

The second size metric is increasingly the height of the laptop. This is the height of the machine with the lid closed and is more about style than anything else. The MacBook Air is one of the thinnest at 20mm, whereas 35mm is about average. As you would expect thinner laptops may mean you have to compromise on price or performance.

Obviously weight is linked to the size metrics - smaller, thinner laptops tend to be lighter. A typical laptops weighs about 2.5kg, whereas a light one is 1.5kg-2kg. Go for lightweight (under 2.5kh) if you are travelling a lot.

There is a lot of debate about which processors/CPUs are better. In a broad generalisation we've classified high/mid/low Intel processors.

If you have the budget always take the latest range.

High end:

Core i5/i7 is the latest range of Intel processors. (i7 being the best)

Mid range:

Core i3

Core 2 Duo - previous generation but still the most available at March 2011.

Lower end:

Pentium Dual Core - previous previous generation.

AMD Athlon

Low end (netbook):

Atom

We are talking about the amount of operating time you can have on the battery - rather than its expected lifetime. Batteries would be expected to last 3.5 - 5.5 hours in a new modern laptop. This diminishes with age of the battery and usage.

You can get better battery life by:

- paying more

- getting a less powerful laptop

- getting a smaller screen

- going for a "Solid State Drive" or SSD instead of a normal hard disk. There are no moving parts so your battery lasts!

The quality of the laptop will matter if you plan to move it around a lot. If you travel once or twice a day with it then it is worth paying for "business-grade" quality. All the major manufacturers have a cheap/home range and mid and high-end professional machines.

A better quality laptop will come with: a more robust keyboard; a tougher case and chassis; and better shock resistance of components if you drop them. The author of this guide has had 3 business grade HPs over 10 years and they have coped admirably with drops and spills, only to be retired gracefully when they became under powered.