Apple did not provide precise sales figures but said Leopard's market performance since its Oct. 26 debut leaves it "far outpacing the first weekend sales of Mac OS X Tiger." Tiger is Apple's predecessor operating system to Leopard -- officially known as Mac OS X 10.5.
Despite the quick start, Leopard has a ways to go if it's to match early sales of Microsoft's Windows Vista -- which debuted in January. Vista sold more than 20 million copies in its first month of availability, according to Microsoft.
Leopard's sprint out of the gate could slow if Apple is unable to solve some major installation problems encountered by early adopters. Among other things, thousands of users said their Macs froze up and displayed the so-called blue-screen-of-death after they attempted to install Leopard.
Various estimates put Apple's overall share of the PC market at between 5% and 6%, but the number drops considerably in corporate environments -- where Macs are usually confined to art and graphics departments. Microsoft aside, Leopard also has to compete with Linux -- a Unix-like open source operating system -- for a larger share of the corporate market. Linux commands more than 12% of the server market, according to researchers at IDC, though it controls only a miniscule portion of the desktop market.
To upgrade to Leopard, Mac users need a machine with at least an 867-MHz PowerPC G4 processor, 512 Mbytes of memory, and 9 Gbytes of available disk space. Leopard will also run on Intel-based Macs.
A single-user upgrade pack is priced at $129, while a Family Pack good for five installations is priced at $199. Leopard also ships preinstalled on a full range of high-end Macs.