ECS 150 STUDY
How are modes transferred safely? - correct answer-saving state/pc/stack pointer/registers
How do you achieve concurrency via processes? - correct answer-Decompose the complex
problem into simpler ones.
Make each simple problem into a process. The resulting process can run concurrently but
each feels like it has its own computer
How does a process go from running to ready? - correct answer-The process calls yield. Or
there is a Hardware Interrupt
How does a process go from the blocked state to the ready state? - correct answer-on
completion of I/O or the signal that blocked it
How does a process go from the ready state to the running state? - correct answer-dispatch
schedule or context switch to that process
How does a process go into the blocked state? - correct answer-If the process was running
and a syscall is made.
How does a process go into the zombie state? - correct answer-exception/fault, or the
process exited, or if a signal was unhandled
How does an application get executed? - correct answer-The loader prepares applications
for execution. It reads the executable file, lays out the code and the data and also
dynamically links to shared libraries
How does hardware support memory protection? - correct answer-segmenting the memory
by a base and a bound, translating with virtual memory. Giving one table per process
How does one switch from kernel mode to user mode? - correct answer--context switch
-new process starts
-return from interrupt, exception, or syscall
-user-level upcall asynch notification to user program
How does one switch from user mode to kernel mode? - correct answer-exceptions or faults,
interrupts, system calls or traps
How does the hardware support dual-mode operation? - correct answer-1. there is a set of
potentially unsafe instructions available only in kernel mode
2. The user is prevented from overwriting the kernel
3. Timer interrupts to periodically regain control from running user processes
4. mode switch - safe way to switch from user mode to kernel mode and vice-versa
, How does the OS execute with limited privilege? - correct answer-slow: execute each prog in
simulator
faster: run unprivileged code directly on CPU.
How is an application created by gcc? - correct answer-1. the preprocessor(cpp) transforms
the program before compiling.
2. The compiler( cc) compiles the program into assembly code
3. The assembler(as) compiles assembly code into relocatable object files
4. The linker(ld) links object files into an executable
How is an application laid out in memory? - correct answer-The application is split into 4
segments:
1. Code - the instructions,the pc points to a location here
2. Data - contains the global variables.
3. Stack
4. Heap
How is dual-mode operation enabled? - correct answer-status bit/extra register
In the micro-kernel, what is put in the OS service layer rather than the kernel? - correct
answer-Networking, file system and device drivers are not sensitive enough to need to be in
the kernel, while job scheduling, memory management and communication should remain
handled by the kernel.
What are components of an operating system? - correct answer-Process management,
memory management, storage management, I/O device management, protection and
security
What are differences between threads and processes? - correct answer-Thread has no
code/data segment/heap of its own. It does have its own stack and set of registers. It has to
be part of a process and there can be multiple within a process. If it dies its stack is
reclaimed. Depending on implementation, each thread can run on a different physical
processor. It is more expensive to context switch to a process. If it dies
What are limitations of OS that prevent concurrency? - correct answer--it is computationally
heavy for the OS to fork a process.
-It is difficult to communicate between processes. Context switch is slow.
What are privileged instructions? - correct answer-changing privilege mode, reading and
writing from/to certain sys registers
halting the processor
performing cache operations
What are process stated? - correct answer-ready, running, blocked, zombie
What are the typical UNIX OS layers? - correct answer-User Level, Kernel Level
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