The latest update of the Apple Mac operating system OS X, known as Snow Leopard, goes on sale on Friday.

The software – available only as a DVD, not a download – was originally due to hit shops in September but Apple brought it forward at the last minute.

The system will go head-to-head with Microsoft’s latest operating system, Windows 7, due for release in October.

Both will also compete with a system from Google, called Chrome OS, set for release in the second half of 2010.

Whilst both Google and Microsoft will offer entirely new operating systems, Snow Leopard is a refinement to its predecessor Leopard.

Graham Barlow, editor of MacFormat Magazine, said the update "streamlines performance"

"[It] doesn’t add that many more features to the previous incarnation of OS X," he said.

The update will retail at £25 in the UK ($29 in US) for Mac users who run Leopard.

A quick tour around Snow Leopard

Apple recommends that owners of older Intel-based Macs that are running the older Tiger OS, should purchase an upgrade which costs £129 ($169 in the US).

The package comes bundled with various other pieces of software, such as iWork, Apple’s Microsoft Office competitor.

However, initial reports suggest that Tiger users can upgrade using the cheaper package.

Apple says that its engineers have "refined 90% of the more than 1,000 projects" that make up the operating system.

Many of these changes are hidden deep inside the software’s code and are aimed at making the system smaller, faster and more responsive.

The firm claim that users who install the update will free around 7GB of hard drive space on average because of the stripped-down code.

Applications should load faster and the machine should also boot up more quickly.

Tweaks will also make it easier for third-party developers to take advantage of the Mac hardware.

However, the system does have some new features.

For example, it is the first operating system to come with inbuilt support for Microsoft Exchange Server, popular email and calendar services used by many companies.

The system will also ships with a new version of the Quicktime player, which will allow users to record and trim their own movies.

Reports also suggest that the ships with anti-virus software for the first time.

"It’s a sign of the times that anti-malware features are appearing in OS X," said Mr Barlow.

"The protection built into Snow Leopard appears to be very basic, but since Macs aren’t under the same threat from the thousands of viruses that affect PCs, it doesn’t need to be particularly advanced.

"It remains to be seen how often Apple will update the malware definitions, and it’s not yet clear whether this is a technology Apple has developed itself or whether it’s using information from a third party."

Apple’s operating system is currently installed in around 3% of personal computers, according to analyst firm Gartner.

Microsoft still commands the market with 95% of machines running a version of Windows.

The open source software Linux trails both, with around 2% of the market.

A review of Snow Leopard will be published on the BBC News website on Monday.

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