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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.
Caches are useful when two or more components need to ex-change data, and the components perform transfers at differing speeds.
Caches solve the transfer problem by providing a buffer of intermediate speed between the components.
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.
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)and(b) the cache is affordable, because faster storage tends to be more expensive.

2.
Interrupt is that causes a computer processor to temporarily stop executing its current program and execute another program instead, finally returning control to the original program. So it prevent that more important task goes back because of less important task. 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.

Interrupts are hardware interrupts, while traps are software-invoked interrupts. Occurrences of hardware interrupts usually disable other hardware interrupts, but this is not true for traps. If you need to disallow hardware interrupts until a trap is served, you need to explicitly clear the interrupt flag. And usually the interrupt flag on the computer affects (hardware) interrupts as opposed to traps. This means that clearing this flag will not prevent traps. Unlike traps, interrupts should preserve the previous state of the CPU.

Yes. User programs create traps for debugging purposes. A trap can be used to call the OS routines or to catch arithmetic errors.



3.
device controller : A device controller is a part of a computer system that makes sense of the signals going to, and coming from the CPU. There are many device controllers in a computer system.
CPU : is an important part of almost every computer. The CPU sends signals to control the other parts of the computer, almost like how a brain controls a body.
4.
Here we describe interrupt handling in a scenario where the hardware does not support identifying the device that initiated the interrupt. In such cases, the possible interrupting devices need to be polled in software.

更新日期：2015/10/15 下午 11:01:18