SAN FRANCISCO - APPLE Inc said the newest version of its Macintosh operating system would go on sale on Oct 26, hitting the market after a four-month delay due to the company's work on the iPhone.

The new version of Apple's OS X software, called Leopard, will cost US$129 (S$189) for a single user and US$199 for a family pack that can be installed on up to five computers in one household.

New features include a file back-up feature called 'Time Machine', improvements to e-mail and instant messaging, the ability to preview documents or files without launching a separate programme, and quick access to other computers on a home or office network.

Leopard marks the sixth version of OS X in as many years, a feat the company is quick to contrast with Microsoft Corp , which went more than five years between new versions of its Windows operating system.

Microsoft's Windows Vista became broadly available early this year and comes in several versions that cost between US$100 and US$260, according to the company's Web site.

'This is going to be great for Mac momentum, which has already been strong for the past few years. This is just one more thing on top of that,' Apple?s vice president of marketing, Phil Schiller, told Reuters in an interview.

In its fiscal third quarter that ended June 30, Apple sold nearly 1.8 million Mac computers, up 33 per cent from a year earlier, a growth rate about triple that of the broader PC market.

Back in April, Apple delayed the release of Leopard to October from its original June target, citing the need to divert software development resources to the iPhone, which was launched in late June.

The company, which also makes the popular iPod digital media player, said its online store is now accepting pre-orders for Leopard. -- REUTERS