An Operating Systems Vade Mecum

120 Space Management Chapter 319. Several processes sharing the same instructions are given separate register sets. (a)Why not let them all use the same registers? (b) Why not divide up the registersand let each process use a different subset in order to avoid duplication?20. We claimed that segmentation hardware can check the subscripts of all array referencesto make sure they are in bounds. When is this claim false?21. Evaluate the suggestion that segments that are brought into main store can be discardedfrom backing store. Under what circumstances would this mechanism beuseful? How could it prove costly?22. Suggest an architecture that would allow Dirty fields for shared segments to be setdirectly by the hardware.23. The translation look-aside buffer on a particular machine has a 95 percent hit rateand takes 100 nanoseconds to yield a value. Main store takes 1 microsecond toread a value. The hardware for address translation needs to make one access to thetranslation table per access and an additional 30 nanoseconds to complete thetranslation. What is the average time per address translation?24. When a process terminates, it may own a number of pages in physical store thathave the Dirty field true. What should be done with these pages?25. A particular database program repeatedly scans an array of 1,000 pages. Each scanstarts with page 0 and continues to page 999. There is only enough main store tohold 100 pages. None of the page-replacement policies given in this chapter doesvery well. Suggest a different policy that will do as well as Min for this program.26. How can the child distinguish itself from the parent after a Split service call?27. Consider a computer that supports two different page sizes, 512 bytes and 4Kbytes. All the pages in a virtual space must be of one size or the other. Whatadvantages can the operating system derive from this ability? How hard is it toachieve these benefits?28. Why is it necessary to use the eager method for updating composite addresstranslationtables when a client updates a privileged-state table?