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Modern concept of the idea, but includes the multiprogramming link’s ability to run different parts of the same program at the same time, the concept expanded to include also threads. The basic idea is that most of the programs may be considered to be an element, i.e. a sequence of smaller tasks. Sometimes these tasks and that is, one by one. For example, step 2, it may be necessary for the operation from this can proceed. In the second case, some programs, you can usefully address all tasks independently of, and other tasks that run without. And, of course, you are confronted with when the task 1, task 2 and 3. the task can be run independently, but must wait for the completion thereof shall be the responsibility of the 4. Another element is that many took advantage of the peripherals, such as tapes and discs, you can also work independently. I/o task such as reading from the disk can trigger a system call in schedule a and left to run independently, while the operating system, review a table suspended jobs and determine which of those that are "runnable" has the highest priority, say The programme a, programme b. is then stored along with a flag indicating its status of waiting, waiting for a disk read. Previously saved under program b then recovered and starts executing the program b. But how the suspended program a when getting again? Well, the i/o device needs a signal that its operation is completed, and this is done with the device. DEVICE interrupts are only peripheral messages system send CPU, it says that they need his attention. For example, when you press a key on your keyboard, the keyboard stores the value of the key sequence and send a break of the CPU, it said that it has data waiting for her. As its name indicates, an interruption can occur at any time, and the kernel must take note, even if no immediate program restart is possible. Reaction from the nucleus to the disruption in this case be would change the status of the program was of "waiting for disk read" to "executable." This restores the program as a candidate for execution, and optionally, its relative priority, program will find its place in the Sun. Deeply nested onion peeling off these layers is a complex business; the key is a lot of overview and faith. Fortunately for Unix offers some simple commands that allow you to run as many programs you may want to and keep track of their progress. Author is having 15+ years experience and providing DBA Services and Online Oracle Tutorials.
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