Introduction to Operating Systems PDF

Introduction to Operating Systems Chapter 1  Class outline Introduction, concepts, review & historical perspective Processes Synchronization Scheduling Deadlock Memory management, address translation, and virtua...

Introduction to Operating Systems Chapter 1  Class outline Introduction, concepts, review & historical perspective Processes Synchronization Scheduling Deadlock Memory management, address translation, and virtual memory Operating system management of I/O File systems Security & protection Distributed systems (as time permits) CS 1550, cs.pitt.edu Chapter 1 2 (originaly modified by Ethan  Overview: Chapter 1 What is an operating system, anyway? Operating systems history The zoo of modern operating systems Review of computer hardware Operating system concepts Operating system structure User interface to the operating system Anatomy of a system call CS 1550, cs.pitt.edu Chapter 1 3 (originaly modified by Ethan  What is an operating system? 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 Chapter 1 4 (originaly modified by Ethan  Operating system timeline First generation: 1945 – 1955 Vacuum tubes Plug boards Second generation: 1955 – 1965 Transistors Batch systems Third generation: 1965 – 1980 Integrated circuits Multiprogramming Fourth generation: 1980 – present Large scale integration Personal computers Next generation: ??? Systems connected by high-speed networks? Wide area resource management? CS 1550, cs.pitt.edu Chapter 1 5 (originaly modified by Ethan  First generation: direct input Run one job at a time Enter it into the computer (might require rewiring!) Run it Record the results Problem: lots of wasted computer time! Computer was idle during first and last steps Computers were very expensive! Goal: make better use of an expensive commodity: computer time CS 1550, cs.pitt.edu Chapter 1 6 (originaly modified by Ethan  Second generation: batch systems Bring cards to 1401 Read cards onto input tape Put input tape on 7094 Perform the computation, writing results to output tape Put output tape on 1401, which prints output CS 1550, cs.pitt.edu Chapter 1 7 (originaly modified by Ethan  Spooling Original batch systems used tape drives Later batch systems used disks for buffering Operator read cards onto disk attached to the computer Computer read jobs from disk Computer wrote job results to disk Operator directed that job results be printed from disk Disks enabled simultaneous peripheral operation on- line (spooling) Computer overlapped I/O of one job with execution of another Better utilization of the expensive CPU Still only one job active at any given time CS 1550, cs.pitt.edu Chapter 1 8 (originaly modified by Ethan  Third generation: multiprogramming Multiple jobs in memory Protected from one another Job 3 Operating system protected from each job as well Job 2 Resources (time, hardware) Memory split between jobs partitions Job 1 Still not interactive User submits job Computer runs it Operating User gets results minutes system (hours, days) later CS 1550, cs.pitt.edu Chapter 1 9 (originaly modified by Ethan  Timesharing Multiprogramming allowed several jobs to be active at one time Initially used for batch systems Cheaper hardware terminals -> interactive use Computer use got much cheaper and easier No more “priesthood” Quick turnaround meant quick fixes for problems CS 1550, cs.pitt.edu Chapter 1 10 (originaly modified by Ethan  Operating-System Operations Interrupt driven (hardware and software) Hardware interrupt by one of the devices Software interrupt (exception or trap): Software error (e.g., division by zero) Request for operating system service Other process problems include infinite loop, processes modifying each other or the operating system  Operating-System Operations (cont.) Dual-mode operation allows OS to protect itself and other system components User mode and kernel mode Mode bit provided by hardware Provides ability to distinguish when system is running user code or kernel code Some instructions designated as privileged, only executable in kernel mode System call changes mode to kernel, return from call resets it to user Increasingly CPUs support multi-mode operations i.e. virtual machine manager (VMM) mode for guest VMs  Process Management A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity. Process needs resources to accomplish its task CPU, memory, I/O, files Initialization data Process termination requires reclaim of any reusable resources Single-threaded process has one program counter specifying location of next instruction to execute Process executes instructions sequentially, one at a time, until completion Multi-threaded process has one program counter per thread Typically system has many processes, some user, some operating system running concurrently on one or more CPUs Concurrency by multiplexing the CPUs among the processes / threads  Process Management Activities The operating system is responsible for the following activities in connection with process management: Creating and deleting both user and system processes Suspending and resuming processes Providing mechanisms for process synchronization Providing mechanisms for process communication Providing mechanisms for deadlock handling  Memory Management To execute a program all (or part) of the instructions must be in memory All (or part) of the data that is needed by the program must be in memory. Memory management determines what is in memory and when Optimizing CPU utilization and computer response to users Memory management activities Keeping track of which parts of memory are currently being used and by whom Deciding which processes (or parts thereof) and data to move into and out of memory Allocating and deallocating memory space as needed Storage Management OS provides uniform, logical view of information storage Abstracts physical properties to logical storage unit - file Each medium is controlled by device (i.e., disk drive, tape drive) Varying properties include access speed, capacity, data-transfer rate, access method (sequential or random) File-System management Files usually organized into directories Access control on most systems to determine who can access what OS activities include Creating and deleting files and directories Primitives to manipulate files and directories Mapping files onto secondary storage Backup files onto stable (non-volatile) storage media  Mass-Storage Management Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time Proper management is of central importance Entire speed of computer operation hinges on disk subsystem and its algorithms OS activities Free-space management Storage allocation Some storage need not be fast Tertiary storage includes optical storage, magnetic tape Still must be managed – by OS or applications Varies between WORM (write-once, read-many-times) and RW (read-write) I/O Subsystem One purpose of OS is to hide peculiarities of hardware devices from the user I/O subsystem responsible for Memory management of I/O including buffering (storing data temporarily while it is being transferred), caching (storing parts of data in faster storage for performance), spooling (the overlapping of output of one job with input of other jobs) General device-driver interface Drivers for specific hardware devices Protection and Security Protection – any mechanism for controlling access of processes or users to resources defined by the OS Security – defense of the system against internal and external attacks Huge range, including denial-of-service, worms, viruses, identity theft, theft of service Systems generally first distinguish among users, to determine who can do what User identities (user IDs, security IDs) include name and associated number, one per user User ID then associated with all files, processes of that user to determine access control Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, file Privilege escalation allows user to change to effective ID with more rights  End of Chapter 1 Operating System Concepts – 9th Edit9on Silberschatz, Galvin and Gagne ©2013