OS Unix Case Study

1. Subject : Operating System Group Members : Muhammad Shakeeb ( IS/17122-Aut -FO7 M ) Syed Zeeshan Nasir ( IS/17133-Aut –F 07 M ) Faisal Muhammad ( IS/17122-Aut –F07 M) Class : BsCS 4th -B

2. Handling Memory

3. • Process A's virtual address space • Physical memory • Process B's virtual address space

5. UNIX was developed on the PDP machines

6. Pre 3BSD system use swapping exclusively to handle memory contention among processes

7. If there is too much contention, processes are swapped out until enough memory is available

9. Demand paging – When a process needs a page and the page is not there, a page fault tot he kernel occurs, a frame of main memory is allocated, and the proper disk page is read into the frame

10. A page daemon process uses a modified second-chance page-replacement algorithm to keep enough free frames to support the executing processes

12. Disk block descriptors

13. Page frame data table

15. Contains the physical address of page and the following bits: Valid: whether the page content legal Reference: whether the page is referenced recently Modify:whether the page content is modified copy on write: kernel must create a new copy when a process modifies its content (required for fork) Age: Age of the page Protection: Read/ write permission Page Table Entry

16. Disk Block Descriptor Swap Device number as there may be several swap devices Block number that contains page

17. Page Frame Data Table Entry Swap use Table entry

18. 11

19. Replacement policy