Term
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Definition
| Only putting part of the process into memory. |
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Term
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Definition
| Loading a page into memory only when a process needs it. |
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Term
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Definition
| Swapping pages into memory rather than whole processes. |
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Term
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Definition
| Pages that are already actually in memory. |
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Term
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Definition
| Move a page into memory only when it is needed. No guessing ahead of time. |
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Term
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Definition
| Generally pages are used frequently in certain sections of a programs execution, but not so much once that section is done. |
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Term
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Definition
| A section of disk that holds pages not present in main memory. |
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Term
| Effective Access Time (for paged memory) |
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Definition
| The time that it takes on average for a page reference. Equals (1-p) x ma + p x page fault time. |
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Term
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Definition
| When a child process is made, initially both share the same pages. When one tries to write to a page, a copy is made for it. |
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Term
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Definition
| Switching out pages that aren't being used for pages that a process needs. Note that if no frames are free, then two page transfers are needed. |
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Term
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Definition
| A bit to indicate that this frame has been written to recently. Set by hardware. This means that if a page has been modified, the changes must be sent to the disk before it is switched out. |
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Term
| Frame-Allocation Algorithm |
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Definition
| Determining how many frames should be allocated to a process that is just starting. |
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Term
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Definition
| A string of memory references that is used to evaluate a page-replacement algorithm. |
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Term
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Definition
| When a new page needs to be used, the oldest page in memory is swapped out. |
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Term
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Definition
| The strange thing that happens when increasing the number of frame actually increases the number of page faults. This usually only occurs for bad page replacement algorithms. |
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Term
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Definition
| Page-Replacement Algorithms that can never exhibit Belady's Anomaly. |
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Term
| Optimal Page-Replacement Algorithm (OPT) |
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Definition
| Replace the page that will not be used for the longest time. Best page replacement algorithm. Also not possible to implement since we can't see into the future. |
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Term
| Least-Recently-Used Page Replacement |
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Definition
| A close second to OPT, and is actually usable. Removes the page that was used least recently. |
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Term
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Definition
| A bit that shows if the page has been looked at in this time cycle. |
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Term
| Second-Chance-Page-Replacement Algorithm |
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Definition
| When a page is selected to be replaces, we check if it has been referenced recently. If it has we go to the next page, and clear the reference bit. Refined FIFO. |
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Term
| Least-Frequently-Used-Page-Replacement Algorithm |
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Definition
| All pages keep a count of how of often it is used. The pages used the least are the ones to be brought out. Can sometimes keep pages in memory that were initially used frequently and now aren't. Can be solved by regularly shifting bits to the right. |
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Term
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Definition
| Give all processes an equal amount of frames. |
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Term
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Definition
| Frames are allocated to a process that is proportional to the size of the process. |
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Term
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Definition
| A process can select a frame to replace from all sets, even ones that it doesn't control. |
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Term
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Definition
| Can only replace frames that it owns. |
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Term
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Definition
| High-activity paging that occurs when a process does not have enough frames, and so spends all of its time swapping out pages rather than execution. |
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Term
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Definition
| A way of reducing thrashing by looking at the number of frames a process currently has. If a page is in active use, it is in the working set. |
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Term
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Definition
| Mapping a disk block to a page and the initial access to the file proceeds through ordinary demand paging. This results in a page fault. This causes a page-sized portion of the file to be read into a physical page. This helps avoid read and write system calls. |
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