http://blogs.msdn.com/b/b8/archive/2012/08/13/collaborating-to-deliver-windows-rt-pcs.aspx
In a blog post this morning, Microsoft confirmed that it has four OEMs (ASUS, Lenovo, Dell and Samsung) for Windows RT tablets. I'm not sure what happened to Toshiba. The same three microprocessor manufacturers (NVIDIA, Qualcomm, and Texas Instruments) are listed as working on Windows RT. Microsoft says the three microprocessors will run on a single code base, meaning there will be one version of Windows RT for all three processors.
Microsoft is making its own version of a tablet for RT, as well. That's a fact that does not sit well with manufacturers like ACER, who see it as unfair competition.
Microsoft says that Windows RT devices will include tablets, tablet+keyboard convertibles, and standard notebook designs. The screen size will be between 10 and 11 inches, and weight will range from about a pound (think 7 inch tablet) to a little more than two pounds (think Macbook Air).
RT is the version of Windows that runs on low power microprocessors based on designs licensed from ARM Holdings, Ltd. ARM-based processors are also used in iPad and Android tablets. I'm sure there are hackers (oops, I mean experimenting programmers) who will be looking for ways to run RT on other platforms, like the Google Nexus 7 and Amazon Kindle Fire. To try to impede these efforts, Microsoft announced that Windows RT software will not be available separate from the purchase of an RT tablet.
The ARM processor design uses power more efficiently than the current Intel designs. So Microsoft is pitching the Windows RT tablet as an "always on, always connected" device. Windows RT will have several levels of activation, from fully on, to on standby but connected, to standby in low power mode, to fully off.
Since ARM processor designs don't run standard Windows software, none of current Windows applications will run under Windows RT. Microsoft is creating an RT-specific version of the Office apps (Word, Excel, Powerpoint). But it's not clear what other Windows software companies are working on a version for RT. I guess we'll learn more when RT is released in October.
It will be particularly interesting to see how the OEMs choose to price their tablets. Android tablet manufacturers found out the hard way that they could not compete with iPad at the same price point. Now Android tablets sell for 25 to 50 percent less that comparable iPad prices. Will the same thing happen to RT tablets?
[Update: Toshiba says it dropped out because of "delayed components." In other words, they couldn't get their act together in time to meet the late October deadline. I expect we'll see Windows RT tablets from Toshiba in early 2013. For now, Toshiba, just like HP, will focus on producing tablets that run the desktop version of Windows 8.]