The memory manager has more or less been rewritten from scratch, with one of the main new features being support for memory managers on the ARM platform. They state the ARM memory manager is rather different from those for x86 chips, but they attempted to have as much code shared between the two different memory managers.
These changes also improve WinDbg support. "WinDbg support is now at a level where the majority of everyday features are working and tasks which previously seemed so distant using WinDbg, such as stepping through the kernel, listing process threads or dynamically editing memory are now working," the announcement reads.
The sound stack has been improved too. "This release brings with it support for wave recording and mixer support such as volume level adjustment and muting," they state, "Improved core component compatibility with WinXP means that more components now run within Windows and goes some way to showing the level of compatibility the sound stack is now achieving."