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13 Cards in this Set

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What are the two modes of operation for the CPU?
-Kernel/protected mode

-User Mode
What services does the kernel provide to user applications?
Process management, ,emory management, file management, device management, network services, access control.
What are the Pros and Cons of a Monolithic kernel?
Pros: easier to implement, faster.

Cons: Security, stability, lasrge size.
What are the Pros and Cons of the Microkernel design?
Pros: More stability, flexibility, maintainability, easier to debug.

Cons: Increased communication overhead, depends on user-level server applications.
What is a modular kernel and how is it better than the other two kernel designs?
Kernel is composed of modules that can be loaded and unloaded while the kernel is running. Better performance than microkernels. Smaller memory footprint than momolithic kernels.
When does kernel code run?
In response to interrupts, faults, or traps.
What happens when an interrupt occurs?
The kernel looks at the interrupt table. From the interrupt table it gets and address. The kernel starts executing from that address. Once done the kernel signals the CPU to return to executing in user mode.
What happens when a fault occurs?
A fault is generated in response to an illegal actions taken by software (ie div by 0 or page fault). Allows the OS to recover without crashing the whole computer. Follows same instructions as an interrupt.
What happens when a trap occurs?
Traps are triggered intentionally. Behaves the same as an interrupt except that the index of the address to execute from in the interrupt table is provided.
What happens when a system call is made to the kernel?
1. The processor switches to kernel mode and begins executing the system call handler.

2. The system call handler uses system call namber to look up the function pointer in the syscall table.

3. The handler calls the actual system call implementation.

4. The results are placed in a return register.

5. The proc exits kernel mode.
True or False: system calls are faster than function calls.
False.
What is a Virtual Machine?
A virtual machine runs multiple OSes simultaneously by creating the illusion that each is running on its own hardware.
What happens when two interrupts arrive simulataneously?
The interrupts are prioritized with a number. lower number = higher priority.