Apple's Mac OS X version 10.5 - known as Leopard - accomplishes the two things one wants when upgrading to a new operating system: it adds a great deal of value and remains familiar. The sixth main release of Mac OS X is not offered in basic, premium or ultimate editions, in which the cheapest software offering has the least number of features. Everyone gets the more than 300 new features packed in Leopard for just HK$1,000 (single-user licence). Stacks appeal Its gorgeous, redesigned desktop interface, called Stacks, brings a clean, snappy way to organise files for easy access. Web, e-mail and other downloaded files are automatically placed in a Downloads stack for a clutter-free desktop. The improved Mac Finder includes the new Cover Flow, a 3D graphical user interface for visually rummaging through files and digital libraries. Quick Look lets you view documents, photos, videos and other files on the desktop without having to open the application that created them. Going postal Apple's mail program has been enhanced to include a range of stationery designs and layouts so you can send personalised e-mails. I tested a new feature called Data Detectors, which automatically senses phone numbers, addresses and events so these can be added to your system's address book. The updated iChat video-conferencing application works like a charm, providing a big boost to collaborative work. Good times The biggest addition to the Mac OS X is the feature called Time Machine, which backs up all data on a machine, finds lost files and restores software. It has a simple one-click set-up, but needs a large external hard-disk drive to function. As with all operating system upgrades, I strongly suggest backing up your present system before installation. There is no reason to believe anything untoward will happen, but it is far better to be safe about such matters.