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10/15 10/8 OS作業
名稱	10/8 OS作業
日期	10/15
課程名稱	作業系統
指導教師	劉艾華

1.(I)Caches are useful when two or more components need to ex-change data, and the components perform transfers at differing speeds.
(II)Caches solve the transfer problem by providing a buffer of intermediate speed between the components.
(III)If the fast device finds the data it needs in the cache, it need not wait for the slower device. The data in the cache must be kept consistent with the data in the components. If a component has a data value change, and the datum is also in the cache, the cache must also be updated. This is especially a problem on multiprocessor systems where more than one process may be accessing a datum.
(IV)A component may be eliminated by an equal-sized cache, but only if:
(a) the cache and the component have equivalent state-saving capacity (that is, if the component retains its data when electricity is removed, the cache must retain data as well)
(b) the cache is affordable, because faster storage tends to be more expensive.


2.(I) An interrupt is a hardware-generated change-of-flow within the system. An interrupt handler is summoned to deal with the cause of the interrupt; control is then returned to the interrupted context and instruction. A trap is a software-generated interrupt. An interrupt can be used to signal the completion of an I/O to obviate the need for device polling. A trap can be used to call operating system routines or to catch arithmetic errors.
(II)Interrupt：Hardware generated interrupt ; Trap：Software generated interrupt
(III)yes
(IV)User programs create traps for debugging purposes. A trap can be used to call the OS routines or to catch arithmetic errors.


3.(I)The differences between CPU and device controller is CPU is the device, that controls all the operations, but device controller translates software input into something a hardware device understands.
(II)The similarity between them is they catch the signals and save the signals in register,and then send the signals out.


4.It stops what it is doing and immediately transfers execution to a fixed location.Receive an interrupt instruction (ex:keyboard,mouse), then go to I/O device to transfer data and send interrupt to CPU when done the job and return control.

更新日期：2015/10/15 上午 02:46:41