I'd like to know how different is development of applications for the Windows Phone 7 OS, in comparison to versions 6.x of that same operating system?
In version 7, is it simple for an application to allocate custom amounts of heap space to process signals such as image and sound?
Also, i read that Windows Mobile 6.x applications are not compatible with version 7, but are version 7 applications compatible with 6.x ?
Thank you for your help.
Taking your last question first, they are not compatible.
On the difference in programming, 6.x uses a modified WinForms front end and a cut-down framework. Windows Phone 7 uses Silverlight and has access to the full framework that Silverlight accesses, this gives you the ability to use things like M-V-VM easily.
The biggest difference is that there is no Unmanaged API to the platform. Everything is C# (and i do mean C#, you can't make VB.NET project or C++/CLI /pure). Windows Mobile 6.5 was a lot like Windows CE API + WinMobileForms(.NET version) and you were able to write your own C++ code, where WP7 is a lot more restrictve.
At the moment there is a choice of either doing Silverlight apps or XNA Studio apps (gaming). Silverlight apps are based on Silverlight 3 spec and XNA studio API is a lot like Zune HD development environment.
One subtle difference between Phone and browser Silverlight is that Phone disables Reflection.Emit API. This means no IL rewrite which is what most IoC containers, O/R frameworks like NHibernate and AOP (Aspect Oriented Programming) tools use.
As for your question about allocating custom amounts of space for image/sound processing. Yes, you will probably be able to do all that assuming that the system allows you to allocate the amount of space you need. The language should not restrict you in that sense, if there are any restrictions, they would be due to the platform, not the language. You should probably read up on game development using managed languages, as there are differences in approach compared to unmanaged languages.
Developer tools and information are available now. I haven't worked with these personally yet, but I understand that the phone emulator really does run the Windows Phone 7 operating system, so the development environment should be sufficient to explore just about everything the phone can do, as long as it's not dependent on phone hardware (e.g., accelerometer).