| A | B |
|---|
| 4 memory allocation schemes | paged, demand paging, segmented, segmented/demand paging |
| Paged memory allocation scheme | Based on the concept of dividing each job into pages of equal size |
| Sectors | Sections of a disk |
| Page Frames | Sections of main memory in paged memory allocation |
| Detemine # of pages in the program | First thing the MM does to prepare to execute a program |
| Logical sequence of pages | First pages contain first instructions of program |
| Storing program noncontiguously | Main memory is used more efficiently |
| Paged memory still requires | Entire job be stored in memory |
| JT, PMT, MMT | Three tables used to keep track of jobs with paged memory |
| Job Table (JT) | Contains size of job & memory location of job's PMT |
| Each active job has own PMT | PMT in paged memory allocation |
| Demand paging | FIRST scheme to remove restriction of having entire job in memory |
| Programs are written sequentially | Demand paging takes advantage of this fact |
| Virtual memory | Most important innovation demand paging made available |
| High-speed direct access storage device | Key to successful implementation of demand paging |
| Predefined policies | Determine when to make room for needed pages |
| Demand paging PMT | PMT with more information than PMT of paged memory |
| Page Fault Handler | Determines whether there are empty page frames in memory |
| Thrashing | Excessive amount of page swapping |
| Page Fault | Failure to find a page in memory |
| FIFO, LRU | Predefined policies to determine when to make room for needed pages |
| FIFO | Removes the pages that have been in memory the longest |
| LRU | Removes the pages that show the least amount of recent activity |
| Working set | Set of pages that can be accessed directly without incurring a page fault |
| Locality of Reference | Only a small fraction of pages referenced during any phase of execution |
| Modules | Logical groups of code |
| Segment | Divisions in the segmented memory allocation |
| Pages | Physical units of fixed size, invisible to program |
| Segments | Logical units of variable size, visible to program |
| Segmented/Demand Paged Allocation | Evolved from demand paging & segmented memory allocation |
| Virtual Memory | Allows the capability of moving pages between main memory & secondary storage |
