I was going to use WES7 (Windows Embedded Standard 7) for the 9. In fact, the 9 was developed in Windows 7!
I had the final hardware, things were working, I got the master image done. Then, to finalize the master image (the one that would be cloned), I enabled EWF (Embedded Write Filter) -- a part of embedded windows that stores all disk writes in ram rather than letting them write to the disk. This way, the state of the operating system is persistent, nothing will wear out over time, and suddenly pulling the power cable doesn't cause problems. All important things for a plug-and-play processing solution.
When enabling EWF, all of a sudden I had severe audio glitches. Turned out that EWF in WES7 causes extreme DPC latency.. Essentially it will sometimes just sit there and hog the CPU without letting anything else run.
So, with
5 days until I was supposed to fly to the US for the first beta installation, I had to make a choice. Try to contact Microsoft and get a fix, or revert to XP embedded since I know that EWF works perfectly there (which would mean splitting the O9 into two processes and rewriting my entire I/O back-end from scratch, to get around the threading limitations in XP).
Considering that I
just heard back from the right person at Microsoft regarding this issue
yesterday -- that is, 8 months after the fact, I'm quite happy with my choice.
So, I bit the bullet and did it. Had I had any choice whatsoever, I would have said it was
impossible to do the work in the allotted time, but I really didn't -- Omnia.9 needed to be released. So, I did it the only way I could which didn't require waiting for anyone else. And, it worked! The 9 performed beautifully on the air at that first beta installation. Heck, that same 9 is still there. We did update the software just a couple of time since then though

.
All that being said, I'd love to use WES7 in future products. Splitting it into two processes (one doing all audio i/o + low latency studio processing, the other doing all the main processing + tcp/ip interface) was a real PITA, so it will be nice not to have to spend time on that. For the 9 the work is already done, so it's probably better leaving it as is, as we would not be able to change the operating system without re-cloning the flash drives. Having 9s out there with two different operating system versions is probably asking for trouble.
///Leif