Several months later than originally expected, Apple's new operating system is here.

Known by its development code name, Leopard, version 10.5 is the sixth major release of Mac OS X (apple.com/macosx).

Apple is gushing with pride, as you'd expect, and lists no less than 300 new features that will, it hopes, make people flock to the shops to buy it.

Many of these features are welcome indeed, but most will only be significant to long-time Apple users. The rest of the world probably doesn't care that the OS X file manager application, the Finder, is hugely improved and faster than it has ever been.

One or two of the trumpeted new features will interest everyone. The most exciting is called Time Machine, and it's a triumph because it makes backing up easy and interesting.

The vast majority of people don't back up their computers, which is a foolish policy. The hard disks we all depend on are fragile things; it's not a matter of "if" your hard disk will fail, it's "when".

That hard fact still doesn't make people back their stuff up. Then they complain when their computers die unexpectedly, and everything is lost.

Time Machine is the first backup software that makes backup so easy.

All it requires is one click to turn it on, and after that you can forget about it. The software will keep your entire computer backed up on a separate disk (you'll need one of these, but they are very cheap these days).

Chances are most people "will" forget about Time Machine, until the day comes when something has disappeared, been accidentally deleted, or a file corrupted. Then they will dive back through time, complete with a science-fiction starscape backdrop as part of the Time Machine interface, and find their missing data.

It looks cheesy, but it works. The first time you use it, it brings a smile to your face. No other backup software has ever achieved that before.

On the whole, though, Leopard is about more than the 300 hyped features. It's all about fine-tuning and refining what was already a very impressive operating system.

Leopard is packed full of tiny details, changes that only Mac experts would notice or be remotely bothered about. They improve the system, make it easier to understand and faster to operate.

Other great new features are included with hardly a mention from Apple.

Screen Sharing is a new implementation of an old technology, but in short it makes it childishly simple to take control of another Mac on your network, or across the internet using Apple's iChat application.

Fantastic news for nerds who find themselves as honorary tech-support geeks to the rest of their family.

Leopard has to appeal to two groups of people. First, the existing Apple users who are perfectly happy with their copies of the last major OS X release, 10.4. It pulls them in with the refinements and perfections present throughout the system.

Second, though, it wants to pull in a few Windows users - those 300 new features will appeal to them a lot more.