Any new Windows release is A Big Deal, but today's is A Really Big Deal.
That's mostly because it will mark the beginning of the end for Windows 8 and the beginning of the beginning for its replacement Windows 9.
Now in our book Win 8 has been a bit hard done by - it set out with lofty ambitions to unite desktop and mobile (or at least tablet) forms, and in many ways succeeded. But reviews were generally mixed and sales never really set the world alight either, so Microsoft will presumably be glad to see the back of it.
So what do we know about it?
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1. It'll be unveiled in San Francisco today
Of course Microsoft isn't admitting that today's event will see the launch of the new OS, instead merely stating that “On September 30, we will be providing an update on what’s next for Windows and the enterprise.”
But as is traditional in tech circles these days, there have been plenty of leaks surrounding the event, and these all point to the fact that we'll see the new OS, or at least a developer preview version of it.
2. It'll almost definitely possibly be called Windows 9
Except it won't. Well not at first.
Windows officials have thus far been adament that the new release doesn't yet have a name, which might make it quite difficult for them to talk about it onstage tomorrow.
That said, the head of Microsoft France, Alain Crozier, reportedly referred to the new OS as Windows 9 in a presentation, before backtracking and repeating the 'it doesn't yet have a name' mantra.
There's next to no chance of that being the OS' full name by the time a consumer release comes around, but it's possible that Microsoft will stick with that term for the present. In the long term, Windows 9 seems much more likely, although some rumours have also speculated that it might just be called Windows or even something entirely different and completely unexpected. OS Y, maybe...
3. It'll be free...
...for some users at least.
We can thank the President of Microsoft Indonesia Andreas Diantoro for this one. According to a report in Indonesian website Detik, Diantoro confirmed that Win 9 would be a free upgrade for all Windows 8 users. Whether that offer will extend to Windows Vista and XP users remains to be seen, but it's unlikely to be a pricey upgrade either way.
4. It'll mark the return of the Start Menu
Microsoft confirmed that the Start Menu would return way back at its Build 2014 conference in April, so it's hardly news, but given the widespread wailing and gnashing of teeth that followed its omission from Windows 8 it's sure to be a popular decision.
Several screenshots of the new Start Menu have now leaked - if you're interested, you can check them out here. Alternatively, you could just, like, wait a few hours until they're released officially by Microsoft.
5. It'll get Cortana
The Halo-inspired virtual assistant has been a key figure in Windows Phone since its 8.1 update earlier this year, but the word is that she'll also be set for a prominent role inside Win 9. A report in Neowin confirmed as much, while also stating that Cortana is both more stable and more powerful in her new home. World domination beckons.
6. It'll be out next year
Rumours concerning its full release date have covered everything from February to September 2015, so let's just be honest and admit that we don't know.
Unfortunately, there'll be no live stream of Microsoft's event, but we'll have all of the news from it as it happens, so keep checking Stuff.tv from 6pm UK time.
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