 Introduction, concepts, review & historical perspective  Processes ◦ Synchronization ◦ Scheduling ◦ Deadlock  Memory management, address translation, and virtual memory  Operating system management of I/O  File systems  Distributed systems (as time permits) CS 1550, cs.pitt.edu (originaly modified by Ethan L. Miller and Scott A. Brandt) Chapter 12

 A program that runs on the “raw” hardware and supports ◦ Resource Abstraction ◦ Resource Sharing  Abstracts and standardizes the interface to the user across different types of hardware ◦ Virtual machine hides the messy details which must be performed  Manages the hardware resources ◦ Each program gets time with the resource ◦ Each program gets space on the resource  May have potentially conflicting goals: ◦ Use hardware efficiently ◦ Give maximum performance to each user CS 1550, cs.pitt.edu (originaly modified by Ethan L. Miller and Scott A. Brandt) Chapter 13

 Goal: really large memory with very low latency ◦ Latencies are smaller at the top of the hierarchy ◦ Capacities are larger at the bottom of the hierarchy  Solution: move data between levels to create illusion of large memory with low latency Chapter 14 CS 1550, cs.pitt.edu (originaly modified by Ethan L. Miller and Scott A. Brandt) Access latency 1 ns 2–5 ns 50 ns 5 ms 50 sec < 1 KB 1 MB 256 MB 40 GB > 1 TB Capacity Registers Cache (SRAM) Main memory (DRAM) Magnetic disk Magnetic tape Better

 Process: program in execution ◦ Address space (memory) the program can use ◦ State (registers, including program counter & stack pointer)  OS keeps track of all processes in a process table  Processes can create other processes ◦ Process tree tracks these relationships ◦ A is the root of the tree ◦ A created three child processes: B, C, and D ◦ C created two child processes: E and F ◦ D created one child process: G Chapter 15 CS 1550, cs.pitt.edu (originaly modified by Ethan L. Miller and Scott A. Brandt) A B EF CD G

Chapter 16 Potential deadlock Actual deadlock

 Scheduling the processor among all ready processes  The goal is to achieve: ◦ High processor utilization ◦ High throughput  number of processes completed per of unit time ◦ Low response time  time elapsed from the submission of a request until the first response is produced

 Long-term: which process to admit?  Medium-term: which process to swap in or out?  Short-term: which ready process to execute next?

 The selection function determines which ready process is selected next for execution  The decision mode specifies the instants in time the selection function is exercised ◦ Nonpreemptive  Once a process is in the running state, it will continue until it terminates or blocks for an I/O ◦ Preemptive  Currently running process may be interrupted and moved to the Ready state by the OS  Prevents one process from monopolizing the processor

 First-Come, First-Served Scheduling  Shortest-Job-First Scheduling ◦ Also referred to as Shortest Process Next  Round-Robin Scheduling

Process Arrival Time Service Time Service time = total processor time needed in one (CPU-I/O) cycle Jobs with long service time are CPU-bound jobs and are referred to as “long jobs”

 Selection function: the process that has been waiting the longest in the ready queue (hence, FCFS)  Decision mode: non-preemptive ◦ a process runs until it blocks for an I/O

 Selection function: the process with the shortest expected CPU burst time ◦ I/O-bound processes will be selected first  Decision mode: non-preemptive  The required processing time, i.e., the CPU burst time, must be estimated for each process

Selection function: same as FCFS Decision mode: preemptive  a process is allowed to run until the time slice period (quantum, typically from 10 to 100 ms) has expired  a clock interrupt occurs and the running process is put on the ready queue

 Subdividing memory to accommodate multiple processes  Memory needs to be allocated to ensure a reasonable supply of ready processes to consume available processor time 17

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 Equal-size partitions ◦ Any process whose size is less than or equal to the partition size can be loaded into an available partition ◦ If all partitions are full, the operating system can swap a process out of a partition ◦ A program may not fit in a partition. The programmer must design the program with overlays 19

 Main memory use is inefficient. Any program, no matter how small, occupies an entire partition. This is called internal fragmentation. 20

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 Base register ◦ Starting address for the process  Bounds register ◦ Ending location of the process  These values are set when the process is loaded or when the process is swapped in 23

 Partition memory into small equal fixed- size chunks and divide each process into the same size chunks  The chunks of a process are called pages and chunks of memory are called frames  Operating system maintains a page table for each process ◦ Contains the frame location for each page in the process ◦ Memory address consist of a page number and offset within the page 24

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 All segments of all programs do not have to be of the same length  There is a maximum segment length  Addressing consist of two parts - a segment number and an offset  Since segments are not equal, segmentation is similar to dynamic partitioning 28

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 Logical ◦ Reference to a memory location independent of the current assignment of data to memory ◦ Translation must be made to the physical address  Relative ◦ Address expressed as a location relative to some known point  Physical ◦ The absolute address or actual location in main memory 30

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 Symmetric multiprocessing (SMP) ◦ Each processor runs an identical copy of the operating system. ◦ Many processes can run at once without performance deterioration. ◦ Most modern operating systems support SMP  Asymmetric multiprocessing ◦ Each processor is assigned a specific task; master processor schedules and allocates work to slave processors. ◦ More common in extremely large systems

 Distribute the computation among several physical processors.  Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as high- speed buses or telephone lines.  Advantages of distributed systems. ◦ Resources Sharing ◦ Computation speed up – load sharing ◦ Reliability ◦ Communications

 Definition: Tightly-coupled CPUs that do not share memory  Also known as ◦ cluster computers ◦ clusters of workstations (COWs) CS 1550, cs.pitt.edu (originaly modified from MOS2 slides by A. Tanenbaum)35

 Interconnection topologies (a) single switch (b) ring (c) grid (d) double torus (e) cube (f) hypercube CS 1550, cs.pitt.edu (originaly modified from MOS2 slides by A. Tanenbaum)36