The UNIX operating system is a 32-bit,
virtual memory, demand paging operating system.
The most important aspects of this
for developers familiar with the DOS architecture are:
The UNIX operating system is a preemptive
This means that the program
does not need to relinquish control to the kernel
in order to switch tasks.
When more than one process accesses a file
or other resource,
the application must be coded to synchronize that access.
For example, a file may need to be locked
before it is updated, to ensure that another process
does not try to update that file at the same time.
Both advisory and mandatory file locking
are supported on embedded systems.
The program does not need to be aware
of any other programs running at the same time.
In particular, it does not need to be aware
of concurrent access of devices
(such as hard disks) by other programs.
The UNIX kernel supports machine virtualization by:
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