[Karunamon]

And they made a number of legitimate attempts to clamp down on that. First with CD keys, then with online activation, then Windows Genuine Advantage. Of course, they didn't succeed, because the phrase "successful DRM" is an oxymoron.

[wongarsu]

Their attempt to clamp down on that only really started with Windows XP, when they already had a near-monopoly. Earlier version technically had a CD Key, but I don't think those actually did anything as long as you passed the key along together with the CD.

[dagw]

They didn't really try to clamp down until they'd become really dominant. Up until Windows XP they basically did nothing to stop you pirating Windows.

[erwinkle]

Yep! Apple had the upper hand with this by having limited hardware compatibility.