About kernel structure

DOS was designed for running only one dsedicated process.
    => Is the perfect for some real-time, dedicated applications.

UNIX, however, was designed for multi-user, multi-tasking applications.

Kernel runs in privileged mode, and can see the physical memory and physical devices, ports.

Kernel structural organization: divide into two function block
    lower function block - consist of devices drivers, VM manager, scheduler, swapper(pager), initialization code.
    upper function block - system call processing functions.