cop5615fa11quiz1Key

cop5615fa11quiz1Key - Quiz 1 Key COP 5615 Fall 2011 1)...

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Unformatted text preview: Quiz 1 Key COP 5615 Fall 2011 1) Describe the steps taken when a user process executes a system call requiring use of a memory mapped DMA device. Include the component that is performing the operation at each step along with the step itself. 2) What are the most significant differences between CASs and Network OSs? KEY 1) Steps taken for I/O call (6) a) Hardware (as execution of the trap instruction) saves program counter value, etc. to stack and switches to kernel mode protection, then reads system call number from register, which is used to load first instruction of call handler from table b) Assembly language procedure saves register values, etc. to process table entry, sets up new stack c) device driver is called to set up DMA writes parameters to device controller giving it main memory address where data is to be read/written, device location to write to/read from, number of bytes to transfer, etc., then write a bit to start DMA, causes process state to be set to blocked, notes the PID blocked on this request d) (Scheduler is run to decide which process runs next, next process dispatched) e) (When I/O is done, system receives H/W interrupt, does actions similar to a-c above, then calls driver, which determines that process is unblocked, changes process state to ready, then runs scheduler) 2) Big differences between CASs vs. Network OSs (4) a) NOS is aimed at remote access and interoperability, while CAS is aimed at service composition and transparency b) CAS supports automated resource/service discovery with broker services, NOS does not c) CAS supports automated referral from one service to another, in NOS this is done by the user, if at all ...
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