distinguish between user mode and kernel mode?
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Answer Posted / rhino
Kernel Mode (System Mode) :
in this mode executing code has complete and unrestricted
access to the underlying hardware. It can execute any CPU
instruction and reference any memory address.
Kernel mode is generally reserved for the lowest-level,
most trusted functions of the operating system. Crashes in
kernel
mode are catastrophic; they will halt the entire PC.
When the CPU is in kernel mode, it is assumed to be
executing trusted software, and thus it can execute any
instructions
and reference any memory addresses (i.e., locations in
memory).
The kernel (which is the core of the operating system and
has complete control over everything that occurs in the
system)
is trusted software, but all other programs are considered
untrusted software.
Thus, all user mode software must request use of the kernel
by means of a system call in order to perform privileged
instructions, such as process creation or input/output
operations.
User Mode :
In User mode, the executing code has no ability to directly
access hardware or reference memory. Code running in user
mode must delegate to system APIs to access hardware or
memory.
Due to the protection afforded by this sort of isolation,
crashes in user mode are always recoverable. Most of the
code
running on your computer will execute in user mode.
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