Difference between user mode and kernel mode: User mode is where all the user programmes will execute. Where as in kernel mode all kernel programmes like like Network driver programs etc., will be execute Kernel mode has has full access to every resource. It is the mode in which the Windows kernel runs. User mode has restricted access to resources. The Linux kernel was non-preemptive through Version 2.4. That is, while a process is in kernel mode, it cannot be arbitrarily suspended and replaced by another process (i.e., preempted) for the duration of its time slice (i.e., allocated interval of time in the CPU), in contrast to user mode, except when it voluntarily relinquishes control of the CPU. Processes in kernel mode can, however, be interrupted by an interrupt or an exception. A process running in user mode can't read or write directly to OS memory. A process running in kernel mode can do it directly. User mode programs are running in application level and Kernel mode programs are running in system level.
