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computing topic 2 - OS (Types of OS (Multi tasking - allow computer to…
computing topic 2 - OS
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Management
Memory management
Segmentation - The allocation of segments or sections in memory to allow a process to run. Each segment can be a different length.
Pagination - Used in virtual memory, each page is a fixed size. The memory manager gives each page a number and records it in a page table. Each process can be split across several pages, pages for a process don't have to be next to each other.
Virtual memory - When main memory is full, the least use page(s)/segment(s) are moved into virtual memory, which is on secondary storage. The new program is then loaded into main memory. If VM is used too often, disk thrashing can occur, which reduces the speed of the computer.
CPU manangement
Interrupts and polling
Interrupts - a signal for the CPU to stop what it is doing and instead carry out the interrupt task. The current task gets pushed to a stack after finished the FDE cycle. Once the task is complete, the CPU goes back to the original task. Interrupts are based on priority, interrupts can be interrupted.
Polling - the CPU or program regularly checks to see if an event or peripheral needs attention. It it does, then the related polling task is carried out.
Scheduling - Allows better CPU efficiency, makes maximum use of resources, gives the illusion of multitasking
Round robin - creates a queue of processes, each process is given a set amount of CPU time. If completed in this time, CPU goes to next process. If not finished, process goes to the back of the queue.
First come first serve - Similar to round robin, but each process is allowed to finish before CPU moves to the next
Shortest job first - processes put into a queue based on length. New job get put into the queue accordingly. Based on number of FDE cycles. May take a while for long jobs to be completed.
Shortest time remaining - similar the SJF, but does it based on FDE cycles remaining rather than total FDE cycles.
Types of OS
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Multi user - allows multiple users, on different workstations, to access a single, powerful computer via a network.
Distributed OS - controls a number of computers at the same time in order to undertake a single computer-intensive task. Each computer contains part of the overall OS.
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Embedded OS - OS that is designed to perform a specific function within its embedded system. Embedded OS' are completely different to one another.
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