Each process that runs in memory allocates space in memory to store its code and data. This space consists of memory pages. Each memory page is 4 KB in size in x86 systems. All the processes address their memory spaces with virtual addresses, which are translated into physical addresses by the system itself with no interaction by any process.
In modern operating systems, there are two categories of the running processes: processes run in user mode and others run in kernel mode. The difference between both modes is the level of access that is granted to the operating system. In the user mode, the processes can't modify paging or access other processes' memory locations except some inter-process communications using Windows APIs. All the processes start in user mode, except the SYSTEM process.
Kernel mode is used by the Windows kernel at system booting to set up memory space and paging. In some situations, such as executing the Windows API, the processor receives interrupt,...
