Microsoft is set to make available to users substantial updates to at least some of its core Windows 8 and Windows RT applications this week.

Microsoft officials announced on March 25 that starting tomorrow, March 26, they'll make available via the Windows Store significant updates to the Mail, People and Calendar apps that are built into Windows 8 and Windows RT.

Update: Microsoft began rolling out these updates late on March 25. If you don't see the updates listed for download, you can proactively check for them. To do this, you must be inside the Windows Store app. From there, swipe in from the right to get the Charms. Then go to Settings and App Update to see if there are any available apps ready for download. Since putting the new Mail app on my Surface RT, I've noticed much-improved mail performance. Huzzah!

For a list of all the new features that will be part of this push, check out my ZDNet colleague Ed Bott's post on the Mail/Calendar/People updates . Like many early Windows 8/Windows RT, users, I'm happy to see Mail get updates like the ability to create and delete folders and the ability to search for mail on the server, among others. Supposedly performance of all three apps is improved, even on low-power Surface RT devices.

But what about the other "core" Windows 8 and Windows RT apps -- especially Xbox Music, which has felt half-finished since it debuted as one of the bundled apps Microsoft delivered last October with Windows 8 and Windows RT? Today's blog post from the Windows services team is solely about Mail/Calendar/People. But according to one of my sources, who mentioned the coming March core-app updates, Xbox Music and the Bing AppEx applications were supposedly going to be refreshed this month , too.

There are still six more days in March, so it could happen. Or maybe these won't actually roll out until April.

I asked my original tipster whether the Xbox core-app refresh is imminent and was told that the Xbox Entertainment app team was still releasing minor internal updates over the weekend, but that they are "almost done."

Update: The Xbox Music update is available as of March 26. It's by no means a huge update, but it does provide performance improvements and more granular controls for volume, semantic zoom and playlists, according to those who've already grabbed the update.

The Bing AppEx team apps -- Weather, News, Sports, etc., which shipped preinstalled on Windows 8 and Windows RT -- may be poised for new updates. So far, no word from the Bing team on that, however.

Late last week, some of us took the appearance of a list of Microsoft-developed apps in the System Log on our machines that the expected refreshes of all the core Windows 8/Windows RT apps were set to arrive imminently.

It turns out this may be unrelated, as Martin Geuss from drwindows.de noted over the weekend. Geuss said that all core apps are listed in the event entry on Windows 8 and Windows RT systems because all of these apps have received at least one update since Windows 8 and Windows RT RTM'd.

Event-entry relevance aside, the expected and (hopefully) useful core app updates are on their way.