Operating Systems COP 4600 Final Exam fall 2019 - Montagne

Virtual Memory - A technique that allows us to run programs whose logical address space is larger than the physical address space TLB stands for - Translation Lookaside Buffer Translation Lookaside Buffer - TLB contains a subset of the page table to speed up memory access (like cache) Hit in TLB - Go directly to Frame Table Miss in TLB - Go to Page Table then the Frame Table Four things needed to implement virtual memory - -Divide memory into Frames -Divide programs into Pages -Page Table and TLB -Hard Drive How many I/O operations are executed if the is a miss in the TLB - 0 if page is currently in memory 1 if memory is full and dirty bit = 0 2 if memory is full and dirty bit = 1 How many I/O operations are completed if the is a Page Fault ( AKA a miss in the Page Table) - 1 if memory is full and dirty bit = 0 - Or - there is a free frame 2 if memory is full and dirty bit = 1 Internal Fragmentation - allocated unused space in a program from fixed partitions in paging External Fragmentation - space in between programs in memory when programs are moved Implicit I/O - I/O created by the system when page faults occur. Explicit I/O - I/O instructions placed programmer placed in program What does EAT stand for? - Effective Access Time EAT Equation - EAT = h ( TLBat + Mat ) + (1-h)(TLBat + 2Mat )