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• What is an Operating System? • Various systems and their pros and cons – E.g. multi-tasking vs. Batch • OS definitions – Resource allocator – Control program – Kernel Abstract View of System Components Important OS Features/services • • • • • • • • Process Management (CPU scheduling) Main Memory Management File Management I/O System Management Secondary Management Networking Protection System Command-Interpreter System OS Control Structure Memory Tables Process Image Memory I/O Tables I/O File File Tables Processes Primary Table Process 1 Process 2 … Process N User data User program System stack PCB Process State Diagram dispatch admit New Ready Running time-out activate release event wait Suspend Blocked suspend Exit • System call vs. System program Dual mode operation & why ? OS structure & Layered Approach • The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface. • With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers. UNIX System Structure Process Management • • • • Process vs. Thread creation Process scheduling Process Termination Unix process creation fork() & exec() – Identify parent vs. child • How to find out process infomation Process Control Block (PCB) Process vs. Thread creation Multithreading Models • Many-to-One • One-to-One • Many-to-Many ---------------------------------------------• Pthread, JAVA thread, Kernel vs. User thread CPU Switch From Process to Process Process Scheduling Queues • Job queue – set of all processes in the system. • Ready queue – set of all processes residing in main memory, ready and waiting to execute. • Device queues – set of processes waiting for an I/O device. • Process migration between the various queues. Representation of Process Scheduling Schedulers • Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue. • Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU. • Midterm scheduler Addition of Medium Term Scheduling Context Switch • When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process. • Context-switch time is overhead; the system does no useful work while switching. • Time dependent on hardware support. Process scheduling Process scheduling Concepts • Maximum CPU utilization obtained with multiprogramming • CPU–I/O Burst Cycle – Process execution consists of a cycle of CPU execution and I/O wait. • CPU burst distribution • Pre-emptive and none-preemptive Scheduling Criteria • CPU utilization – keep the CPU as busy as possible • Throughput – # of processes that complete their execution per time unit • Turnaround time – amount of time to execute a particular process (finishing time – arrival time) • Waiting time – amount of time a process has been waiting in the ready queue • Response time – amount of time it takes from when a request was submitted until the first response is produced, not output (for time-sharing environment) Various scheduling algorithms • • • • • • • • FCFS SJF SRTF R-R with quantum Priority Multi-level Priority --------------Pros and cons, different conditions (q time, starvation prevention etc.) • Example of process arrival rate Process Communication • IPC & Unix IPC • Client-Server – Raw socket – High-level comm (e.g. RPC, RMI, CORBA etc) – Pros & con on various mechanisms Process Synchronization & deadlocks • • • • Critical Section Semaphore & implementation (Unix) Spin lock and sleep(wait) lock Deadlock – Mutex, hold-wait, no-preemption, circular-wait – Identify deadlock from resource allocation graph or code Memory Management • • • • • • • • Swapping Contiguous Allocation Paging Segmentation Segmentation with Paging -------------------Pros and cons Address translation Pros & cons • Paging vs Contiguous • Hierarchical Paging vs. Hashed Page Tables vs. Inverted Page Tables Example of address translation (segmetation) Example of address translation Virtual Memory Virtual Memory • Demand paging • Demand segmentation • Page fault and how to handle • Page replacement File Management • • • • • File structure File Attributes (FCB) directory Access method Access control A Typical File Control Block Virtual File System Allocation Methods • An allocation method refers to how disk blocks are allocated for files: • Contiguous allocation • Linked allocation • Indexed allocation I/O system • I/O Hardware • Application I/O Interface • Kernel I/O Subsystem – Chracter vs. block – Polling vs. interupt User program & Kernel interface Note: This picture is excerpted from Write a Linux Hardware Device Driver, Andrew O’Shauqhnessy, Unix world Two I/O Methods Synchronous Pooling or interrupt Asynchronous LKM • What is it? • Pros & cons (vs. recompile and patches)