Within days of Apple’s forthcoming Snow Leopard operating system – officially called Mac OS X 10.6 – being put on the Amazon site for online pre-orders, the OS has already notched the top rank on Amazon.com’s software best-seller list!

However, Amazon’s Snow Leopard sales pages remind the customers, listing themselves for pre-orders for Apple’s new OS, that the system is scheduled for launch in September.

The Amazon pages pertaining to the pre-orders mention: “You may pre-order it now and we will deliver it to you when it arrives.”

The Snow Leopard will be available - a month before Microsoft’s Windows 7 OS - at a $29 upgrade price for a single license, and a $49 price for a “family pack” comprising a maximum of five licenses.

While the pre-orders for the $29 pack of the Mac OS X have recently bagged the top rank on Amazon's software sales chart, the pre-orders for the $49 pack were in the second place.

Though Apple had introduced Snow Leopard OS in June last year, the cost was revealed almost two months back at the company’s annual developers’ conference. Announcing the pricing, Craig Federighi, VP of Mac OS engineering, had said at that time: “Leopard was $129 but we want all Leopard users to upgrade to Snow Leopard, so we're pricing it at $29.”