The IBM System/370 architecture uses a two-level memory structure and refers to the two levels as segments and pages, although the segmentation approach lacks many of the features described earlier in this chapter. For the basic 370 architecture, the page size may be either 2 Kbytes or 4 Kbytes, and the segment size is fixed at either 64 Kbytes or 1 Mbyte. For the 370/XA and 370/ESA architectures, the page size is 4 Kbytes and the segment size is 1 Mbyte. Which advantages of segmentation does this scheme lack? What is the benefit of segmentation for the 370?
Answer to relevant QuestionsAssuming a page size of 4 Kbytes and that a page table entry takes 4 bytes, how many levels of page tables would be required to map a 64-bit address space, if the top-level page table fits into a single page? A key to the performance of the VSWS resident set management policy is the value of Q. Experience has shown that with a fixed value of Q for a process, there are considerable differences in page fault frequencies at various ...Briefly define feedback scheduling. Define residence time Tr as the average total time a process spends waiting and being served. Show that for FIFO, with mean service time Ts, we have Tr = Ts/(1 – p), where p is utilization. What is the difference between hard and soft real-time tasks?
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