So many people think Microsoft will lose all Windows 10 profits and revenue, but they only said they're offering a free upgrade. They never said they'd stop charging OEM's a fee for each Windows licence they buy. Thus they may have a few hundred million hit on profits and revenues, but other than that we should expect good earnings for Microsoft. Plus we'll see a larger market share for Windows 10. Also they didn't say the business version is going to be free. And with the free upgrade, we should expect people to buy more Microsoft products (like more office licences or maybe an xbox live card with the savings). So in the end, it'll even out. And I'll repeat this it'll help it increase its market share of not only Windows 10 but against linux, mac, ect.

Why would a free upgrade increase the market share? If anything, it will slow down the decline...

Because as of right now Windows 10 has no market share. And Win 7 - 8.1 has about 70%. Those people are able to upgrade.

Since it would convice more people to upgrade to Windows 10. Windows 7 and 8 users would flock to the one year deal, plus with a more familiar UI, OEMS would sell more devices, thus increasing market share.

I think it's because more people are inclined to upgrade for free and there are probably a lot of Windows 7+8 users.

My question was not pertaining to W10, but against Linux, Mac, Android...as the OP said.

Even if all W7 and W8 users upgrade for free, Windows marketshare will still remain the same...

I'm assuming they'll still earn fortunes from enterprise licenses.

My feeling is that they want to leverage familiarity with their desktop platform to expand their mobile market share. A good starting point for this would be to encourage rapid adoption of the OS on PCs. If the OS is all that it cracks up to be, this could serve to lower the barrier for Windows phone and tablet adoption.

Well I'm sure there is a reason they are offering a free upgrade. Maybe they want more people to use their new services. And anyways, its not like this move is gonna stop people from buying new devices or slow down sales of new PC's.

Because of the return of consumer interst in Windows 10. With a familiar UI returning, and the start menu back, consumer interest would spike. In turn more pc sales (windows).

Well the free upgrade isn't meant for market share increase then. The features should handle that.