Kernel: The Base Operating System

The Windows 32-Bit API on both Window NT-mode and Windows Enhanced-mode provides preemptive thread-based multitasking. It also runs all Windows 32-Bit and MS-DOS applications in separate address spaces so that they cannot corrupt one another.

The Windows 32-Bit API is designed to be portable beyond the 80386 and 80486 processors and in particular to be portable to RISC architectures. All these processors have different features but have in common 32-bit addressing and paged virtual memory architectures. Paged virtual memory is more efficient to implement and executes faster than segmented virtual memory. Memory management in Windows 32-Bit is secure because the operating system places different memory objects in different pages of memory and allows an application to control access permissions (Read, Write, Read/Write, Execute, and so on) to memory objects.

Given a large 32-bit address space, the operating system can conveniently and efficiently optimize file I/O because processes treat the file as a very large memory object and randomly access that object. The operating system, through page faulting, can detect read access to a file and bring in that data. It can detect when a shared file is written to and then write out that data. With process-settable access permissions and sparse allocation of physical memory pages, processes can implement very efficient data access, even when access patterns are entirely unpredictable.