After a fairly confusing and in some cases blatantly incorrect post by Trent who originally wrote this post and who I will ensure doesn't write any hardware related posts again(!) - this post has been updated & rewritten by the comments of one of our readers Alex.

There are two kinds of memory- long term memory which goes on your hard drive; which is where documents are stored. This isn't usually referred to as 'memory' but rather 'hard disk', 'drive' or simply 'space'. Hard drive space limits how much stuff like music you can hold and store.

Then there is the short term memory; which is usually what is meant by the word 'memory'. This is 'volitile' that is, it's all lost when you turn off your computer. It is used to hold temporary data, like the programs you are working on, pictures you're looking at etcetera or the music iTunes will be playing in the next 10 minutes.

The size of 'memory' is what defines how much multi-tasking you can do: and the 'memory' in both versions is the same- 2GB, which is probably more than enough for most of the things you're likely to want to do on a laptop.

The 'hard-drive' is what differs between models.

• The cheaper version is *larger*- 80GB; and is made of moving parts, similar to a CD drive locked in a case. This option uses the same hard drive as a large iPod (the ones you can hear clicking and whirring).

• The more expensive version is highly unusual- it uses 'solid state' memory; with no moving parts. The upside is it's more reliable, uses less power, and is smaller and lighter. It's also faster to read and write from- this means that "memory" and CPU intensive things like image manipulating wont be much different, but reading, moving, deleting, downloading large documents will be faster.

• The downside is it's a lot more expensive, and the more expensive model is actually smaller (64GB). This is the same memory as in use in the iPod nanos.

Apple speculate you will use the time machine function to store most of your data on an external drive (or home desktop) ; and you'll only store current documents on your laptop (or you'll use online facilities like Google Docs).

Thank you for much better, clearer & in fact - correct explanation Alex. Trent, you're fired.

Update

For a thorough technical comparison of the two, have a read of this from Ars Technica