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Next subsection that we're going to go into is dealing with the

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asynchronous events in particular, how we go about, handling them.

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We've already described them at a high level. The hardware exceptions are the things

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like traps and memory faults and arithmetic exceptions. The external

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events are things that are coming from the user. These are

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interrupt quit and stop the primary difference between these is that the

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hardware exceptions occur because of the execution of a particular instruction,

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so,

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You, you dereference a null pointer. There's a particular instruction that we can point

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out and say that's the instruction that was bad or that arithmetic exception.

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That's the instruction that under floater over, floater / 0

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trap traps on a particular memory, typically because you touch a

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piece of memory that's not currently loaded into your address Space,

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by contrast. The external events are not tied to a particular instruction. The

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user Just Hits interrupt when they hit in or up. It's not the fault

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of a particular instruction, it

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It just happens to be. That was the instruction. That was executing at the time that the interrupt got hit, or the

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quit or the stop. I/O events break down into several

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categories. We have either the completion or availability

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of I/O, so you can be notified. For example, that a write

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to disk that you started, has now finished. You can be told about

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I/O that's available. So a packet has arrived on the network and there's

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in the networking world, the ability to have what's called out-of-band Data.

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Data that has come from essentially just jumping the pack to let, you

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know, typically some kind of exceptional condition. Then we course, we have the

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timers which we've already talked about. We have the real-time timers and the

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pair of process virtual timers.