Changes to drivers are documented in detail in the Help. In Windows Embedded CE 6.0, a particular user-mode address might be valid in multiple processes. In previous versions, each process had a unique virtual address space, so this was not a significant consideration. In Windows Embedded CE 6.0, device drivers need to be aware of any process that passes them pointers to memory buffers. This improves the performance of intra-kernel calls that, in previous releases, required multiple traps into the kernel. In Windows Embedded CE 6.0, many system services execute in the context of the kernel. For example, one process managed loadable device drivers, another managed registry and file systems, another managed the windowing system, another managed system services, and so forth.
Previous versions of the OS used special processes to add functionality to the base kernel. The new virtual memory architecture has significant implications for device drivers. The separation of virtual address spaces makes processes more isolated from one another, increasing system robustness and security. This alleviates many of the space concerns for individual processes. In Windows Embedded CE 6.0, each process gets its own unique 2 GB user–mode address space. For example, an application might make a graphics call, which in turn made a device driver call, which then updated the registry this transaction required three kernel traps for a single application operation. In addition, the overhead of making system calls that involved multiple handlers could be significant. As application software increased in complexity, the 32 MB limit became increasingly restrictive.
In previous releases, each process received a 32 MB "slot" within a shared 2 GB user–mode address space. The Windows Embedded CE 6.0 Operating System (OS) features a complete update to the Windows Embedded CE virtual memory architecture.
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