Just days before Microsoft orders OEMs to stop building new PCs with Windows 7 Home Premium, Dell tried one last time to spur sales using the lure of the five-year-old consumer OS.

In a banner that ran on its website over the weekend, Dell promoted Windows 7 systems with the tagline, "Windows 7 for the win," and discounts of up to 30% in a sale that runs until early Thursday.

Dell listed nine notebook and desktop PCs that come equipped with Windows 7 Home Premium, the consumer-grade version that is to be retired by computer makers on Friday, Oct. 31. The least expensive is an Inspiron 15-in. laptop discounted by 26% to $399, the most expensive a 17-in. notebook reduced 21% to $899.99.

Meanwhile, the two other OEMs (original equipment manufacturers) in the top three worldwide -- No. 1 Lenovo and No. 2 Hewlett-Packard -- barely bothered with Windows 7 Home Premium: Lenovo showed none for sale on its U.S. online store, while HP offered just one equipped with the consumer operating system.

Earlier this year, Microsoft set Oct. 31 as the end-of-sales date for new Windows 7 PCs. Before that, the company had first posted the date, then retracted it, then restored it only for consumer systems. Microsoft left the date blank for the halt of Windows 7 Professional installed on new PCs, saying only it was "not yet established."

In February, Microsoft said it would give a one-year notice before it demanded that OEMs stop selling PCs with Windows 7 Professional. Under that rule -- and since Microsoft has yet to deliver the promised warning -- computer makers will be able to continue selling PCs with Windows 7 Professional until at least late October 2015.

An even longer extension is likely: Although the new Windows 10 will be shipping by then, business will be hesitant to immediately move to the new OS. Gartner, for example, has said that most enterprises won't start migrating to Windows 10 until 2016 at the earliest.

With corporations turning a cold shoulder to Windows 8 -- and the ability to conduct "in-place" upgrades from Windows 7 to Windows 10 -- it's probable that those customers will want to continue to purchase Windows 7 Professional PCs after October 2015, and that Microsoft will let OEMs oblige.

It's not surprising that OEMs continue to market Windows 7-based machines, or that Microsoft has extended their use of Windows 7 Professional by almost 12 months so far. PC sales have been in a multi-year slump and neither OEMs nor Microsoft will pass up selling systems, even if that means the computers run an OS that has exhausted nearly half its 10-year support cycle.

That cycle will be one downside to buying a new PC with Windows 7, as Microsoft will stop serving security updates on Jan. 14, 2020. On the plus side, the company has promised that Windows 7 PCs will be upgradeable to Windows 10. It's unknown whether Microsoft will charge for Windows 7-to-Windows 10 upgrades, although analysts expect it to hand Windows 10 upgrades to Windows 8.1 users free of charge.

Because of the extension of Windows 7 Professional PC sales through at least October 2015, Microsoft's computer-making partners will have the ability to equip new systems with three different operating systems -- Windows 7, Windows 8.1 or Windows 10 -- for at least several months next year as the retirement and release dates overlap.

These policies may be made moot, however, by Windows 10, which most believe will be sold and maintained for much longer than past editions, just as Apple has stuck with the OS X nameplate -- pronounced "OS Ten" -- indefinitely.

Windows 8 also faces an approaching deadline: On October 31, retail sales of the 2012 original are to stop, although sales of Windows 8.1 can continue. PCs with Windows 8 may still come off the factory lines -- Microsoft has not set an OEM end-of-sales date -- but that is irrelevant as the denigrated OS has been supplanted by Windows 8.1 on most new machines.