The technical previews have offered an upgrade option, but that's not guarantee it will be included in the final version. Either way, it's almost always better to do a full reinstall for a major version like this.

An upgrade; the underlying technology in Windows hasn't changed significantly since Vista.

It reminds me of the Model Year - We're still on Windows Model Year 2008.

Windows 10 was version 6.4 internally but it sounds like they're going to go make it 10.0 on release.

(Windows 8.1 is 6.3 and Windows 7 is 6.1 and Vista is 6.0)

I haven't used Win10 yet. I'm curious if they've rewritten some of the core components like they did for the 2003-2008 jump. Things like IIS, Task Scheduler engine, & Security (UAC elevation).

That's not correct - Tech Preview already shows the version 10.0.build#

Conceptually Windows 10 would/could have been 6.4, but it isn't.

In the same vein... Windows Vista hadn't changed significantly since XP, or XP since 2000, or 2000 since NT 3.5.1, etc. It's all iterative and subject to perspective here.

2003 -> Vista was the big change. All others were minor by comparison.

Plus we were talking about the deployment/upgrade technology.

But how "big" those changes are, is pretty subjective unless you're talking a pretty narrow context... the UI changed significantly in any number of areas between releases... if you have to access those a lot, that change is huge... to you. Frankly, I don't find any of them too different from each prior version... over time they're more significant.

Necessary? Probably not.

But you should anyways.

It isn't 2001 anymore.

Eh, even with constant upkeep and trimming of all non-essential processes/services, desktop Windows still begins to atrophy from day 1 in a way that one just does not see on *nix machines. Wish it weren't so but such is the price of Windows' legacy baggage.