Computer Science 330
Operating Systems

Fall 2022, Siena College

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Agenda

• Announcements
  • The next readings/activities from OS zyBook: Chapter 7, due Friday, November 18
  • Lab 7: Interprocess Communication [HTML] [PDF] remains due Wednesday, November 16 (do this before starting the new project)
  • Programming Project 4: Roger Bacon Shell with Pipes and Redirection [HTML] [PDF]: aim to get at least the parsing of pipelined commands done within a week
• Exam 2 information
  • In class, Monday, November 21
  • Same ground rules as Exam 1
  • Accounts for 10% of course grade
  • Topics are from Chapters 4, 5, 6, of OS zyBook, Labs 3, 4, 5, 6, Programming Projects 2 and 3
  • Practice problems out, we can spend some time on these in class on Friday, please look at them by then
• Looking at a Programming Project 3: Basic Shell [HTML] [PDF] reference solution
• Looking at (more of) the exercises for OS zyBook Chapter 6
  • Section 6.4, we will do all, 1-5
• Memory Management wrapup and additional info
  • Contiguous allocation
    • hardware support: limit and base/relocation registers
    • first-fit/best-fit/worst-fit
  • Fragmentation
    • external: waste between allocated chunks
    • internal: waste within allocated chunks
    • reduce external fragmentation with a compaction operation
  • Paging
    • break up logical memory into pages, physical memory into frames
    • page size: the size of these pages/frames
    • can allow virtual memory
    • translate addresses by looking up a frame number using the page number, which is part of the logical address
    • store the translations in a page table in memory
    • a memory access now requires a page table access then the memory access - slow!
    • help: translation lookaside buffer - associative memory that stores a subset of table entries
    • TLBs are small, but locality helps it to have an excellent hit rate in practice
    • page table too large? page it - multilevel page tables
• Lab and project time