Windows 8
Shown is a Hewlett-Packard computer tablet with Windows 8 software. REUTERS

The Microsoft Corp. (Nasdaq: MSFT) began accepting preorders of its Windows 8 operating system on Friday, with the price for an upgrade to the full version of the software set at $70, according to Reuters.

If users are patient enough, they can download the new OS to their computers for $40 on Oct. 26. But beware: For those who like to get good deals, this one will expire at the end of January.

Meanwhile, the Windows Phone 8 is scheduled to launch on Oct. 29, Wired reported.

Microsoft customers can reserve the new OS software through, Best Buy, Staples, and other stores.

For those who either bought or will buy a Windows 7-run personal computer between June 2 and the end of next January, they will be eligible to upgrade to Windows 8 Pro for $15.

Microsoft decided to offer the upgrade to avoid a drop-off in PC sales before Windows 8 is launched, Reuters reported.

PC makers such as Acer, Asustek, Dell, Hewlett-Packard, Samsung and Sony are also taking preorders for PCs with Windows 8 preinstalled, Microsoft said.

However, Microsoft did not mention anything about its Surface tablet PC, which is expected to hit the market around the same time as Windows 8. The company hopes it will challenge Apple's iPad and iPad mini.

Microsoft is spending between $1.5 billion and $1.8 billion on its Windows 8 marketing campaign, Forbes reported.

There will be two major changes with Windows 8, Forbes noted. Desktop virtualization must be used to access legacy Windows desktop applications, and the server that supports the Windows RT tablet could be in a traditional corporate data center, a private cloud, or a public cloud such as Microsoft’s Windows Azure.

Computer manufacturers are worried whether it will help the declining PC market, but veteran Microsoft-watcher, Paul Thurrott, believes the company's Metro and RT are the future.

He told Forbes: “By engineering Windows 8 this way, and not just making a separate Metro-only OS for tablets and devices, Microsoft is sending us an implicit but, I think, clear message -- which is that the future of general-purpose computing will occur via devices and not PCs.”

N.B.: This article was changed to reflect the fact that Microsoft has not yet announced the price of the full Windows 8 OS software as a fresh installation, as opposed to an upgrade.