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Brief Virtual Address technique Base/Bounds Segmentation Paging Problems with Segmentation: external fragmentation: free space becomes full of small used spots and free spots intermixed not fully flexible Internal fragmentation e.g. “sparse” heap (data in top and bottom of heap, even though middle part is unused must keep in memory) New Approach: Paging divide virtual address space into small(4KB), fixed-sized units call pages similarly, divide physical memory into 4Kb page frames Free space management: easy (e....

Brief Page Table  Per Process large => in memory Upon every memory reference: address translation What does the hardware need to know? location of page table (Page Table Base Register[PTBR] in MMU) Points to start of page table of currently running process Privileged Paging: Too Slow To do translation: Fetch Page Table Entry Extra memory reference Solution: Hardware (Translation Lookaside Buffer [TLB]) in CPU hardware that holds some number of “popular” translation Method: When Virtual address -> TLB, If VPN is in the TLB, “hit” use PFN in TLB, form physical addr, perform mem access If not, “miss”....

Why build distributed systems? Performance of single computer can’t handle load throughput, latency cost/performance commodity components elasticity incremental scalability Fault-tolerance availability reliability: don’t do something wrong data sharing Why study distributed systems? Important Practical Challenging / Interesting Why is it challenging Faults - Fail-stop, crash slow nodes, misbehaving nodes nodes disagree, who to trust? Interperoleat: lack of global state File A has different content how man jobs on node B?...