OPERATING SYSTEMS OVERVIEW

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A mechanism for scheduling threads or processes. Scheduling can be as simple as running the next thred, or it can use relatively complex rules to pick a running process.

A method for simultaneous CPU execution and IO handling. Processing is going on even as IO (such as disk) is occurring in preparation for future CPU work.

Off Line Processing; not only are IO and CPU happening concurrently, but some off-board intelligent processing is occurring with the IO.



Interrupts:
Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines.
Interrupt architecture must save the address of the interrupted instruction.
Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt.
A trap is a software-generated interrupt caused either by an error or a user request.
An operating system is interrupt driven.


Caching:
Important principle, performed at many levels in a computer (in hardware, operating system, software)
Information in use copied from slower to faster storage temporarily
Faster storage (cache) checked first to determine if information is there
If it is, information used directly from the cache (fast)
If not, data copied to cache and used there
Cache smaller than storage being cached
Cache management important design problem
Cache size and replacement policy