Limited Time: Windows 8.1 OEM (64-bit) for $79.99

Michael Santo's picture has the OEM 64-bit version of Windows 8.1 on sale for $79.99 after coupon code.

The item can be viewed here, with an advertised price of $99.99. The coupon code, "EMCWVXT36," brings the price down to $79.99. The coupon code expires on Dec. 9. Newegg charges sales tax in California, New Jersey, and Tennessee.

As a comparison, has the same item for sale at $96.88. charges sales tax in many locations.

To be clear, this is the OEM or system builder version of the product. As such, it contains only one version -- the 64-bit version -- of the product. The full retail version from Microsoft contains both the 64-bit and 32-bit versions. Notably, the 32-bit version of Windows 8.1 is also sold at Newegg, but does not respond to the coupon code.

This is also -- again, to be clear -- not the Professional version of Windows 8.1.

The details and Microsoft's stance on System Builder licenses can be found here.

The OEM or system builder version of an operating system is the sort of software that is used by Dell, HP and other laptop and PC manufacturers, and comes pre-installed on pre-built machines. It is tied to that machine and in fact, the motherboard. If the motherboard is replaced the serial number is no longer valid. Of course, if Dell were to replace the motherboard of your machine for some reason, that issue will be corrected before it is returned to you.

If, instead, you were the replace the motherboard of your home-built machine yourself, you'd have to tap-dance with Microsoft to get the serial number reactivated. Eventually, if they believe you, they will relent.

It also is not sold in "upgrade" form. That is OK for most of those opting for this option, however, since a clean install is preferred by many, eliminating the dross from the older installation of software.

Windows 8.1 is Microsoft's attempt to meld mobile and desktop. It has two modes, the so-called "Modern-style" UI -- which closely resembles Windows Phone -- and a desktop mode. The desktop mode is similar to that in Windows 7 and earlier OSes. By default, the OS boots into Modern UI mode, but with 8.1 Microsoft has given users the option of going directly to the desktop.

There are also third-party apps that do the same.

In desktop mode, the platform performs much the same way as Windows 7 does, though there are differences. In particular, it's impossible to gain full Admin access for a user account, despite turning off User Account Control (UAC). That is because User Account control isn't "really" disabled unless you change a registry key, which in turn disables Modern UI apps.