Apple has put a countdown clock on its company homepage

Due in June the update was delayed by four months as Apple deployed engineers to work on its iPhone.

Leopard is the sixth version of the operating system to appear since OS X made its debut in 2001.

Apple said it had more than 300 new features onboard including one named "Time Machine" that automatically backs up important files.

Pre-order online

Also inside Leopard is the finished version of the "Boot Camp" utility that allows people to run copies of Windows XP or Vista on their Mac.

In a statement Apple said it hoped the release of Leopard would boost the prospects of its home computers.

Market data compiled by Gartner suggests that Apple is now the third largest computer manufacturer in the US. It has a 6.4% share of the computer market, said the analyst firm, up from 5% a year ago.

Apple owners can pre-order the software via the company's online shop. In the UK the price for a single version will be �85. A family pack, which means it can be installed on up to five computers, will cost �129.