Mac clone maker Psystar has sued Apple for a second time, charging that it illegally ties the new Snow Leopard operating system to its hardware.

The outfit, which is being sued by Apple for breaching rules on what its operating system can do, also asked a federal judge in Florida to rule that the small company has the right to purchase copies of Snow Leopard on the open market and use them to install Mac OS X 10.6 on the machines it sells.

Psystar's lawsuit said that by tying its operating system to Apple-branded hardware, Apple restrains trade in personal computers that run Mac OS X, collects monopoly rents on its Macintoshes, and monopolises the market for 'premium computers'. It pointed to an NPD finding that Apple's share of revenue in the market for premium computers is 91 per cent.

The antitrust angle in the new lawsuit is a repeat of Psystar's strategy of more than a year ago, when it accused Apple of violating the Sherman and Clayton Acts. A federal judge in California tossed out Psystar's claims.

The outfit argues that this time Snow Leopard is completely different. The technical mechanisms used by Apple to tie Mac OS X Snow Leopard to Macintoshes and the technology used by Psystar to get Mac OS X Snow Leopard to run on Psystar computers are new and different and not within the scope of the California litigation, it says.