Physical machine Extended machine Processor(s) Threads Memory Processes

Operating Systems Peter Druschel and Rodrigo Rodrigues MPI-SWS and Saarland University 1 Introduction Required readings: Silberschatz/Galvin: Chapters 1-3 What is an operating system? Layer of software between the hardware and application programs. Two main functions: • Resource manager • Extended (abstract) machine OS as resource manager • mediator/coordinator: resolve conflicting resource demands • protect users from each others (and from themselves) • mechanisms and policies for control of resources, flow of information OS as extended machine • provides stable, portable, reliable, safe, well-behaved environment (ideally) • Magician: makes computer appear to be more than it really is • Single processor appears like many separate processors • Single memory made to look like many separate memories, each potentially larger than the real memory 1 Operating Systems 2 Physical machine Extended machine Processor(s) Threads Memory Processes Disks Files Network adaptors Operating Comm. channels Monitor System Speaker Microphone Clock/Timer What resources need to be managed? • processor(s) (computation) • main memory • secondary memory (disks, tapes, CD-ROM) • network links • I/O devices (terminals, printers, audio, video) OS must • service all of these devices simultaneously, • support safe, efficient, and fair sharing of resources among users and programs. Major issues in operating systems • concurrency —how are parallel activities created and controlled? • sharing —how are resources shared among users? • naming —how are resources named (by programs and users) • protection —how is one user/program protected from another? • security —how to restrict the flow of information Operating Systems 3 • performance —why is it so slow? • structure —how is an operating system organized? • reliability and fault tolerance —how to handle failures • extensibility —how do we add new features? • communication —how and with whom can we communicate? • scale and growth —what happens as demands and resources increase? • persistence —how to make data last longer than programs • distribution —accessing the world of information • accounting —who pays the bills, and how do we control resource usage? Brief history of operating systems • In the beginning, one user/program at a time, no overlap of computation and I/O. OS first appeared as a subroutine library shared by all users. • simple batch systems were first real OS: – OS stored in part of main memory – it loaded a single job (from card reader) into memory – ran the job, printed its output, etc. – loaded next job • Spooling and buffering allowed jobs to be read ahead of time onto tape/disk or into memory. • Multiprogramming systems provided increased utilization – multiple runnable jobs loaded in memory – overlap I/O processing of one job with computation of another – benefit from I/O devices that can operate asynchronously – requires use of interrupts/DMA Operating Systems 4 – tries to optimize throughput • Timesharing systems support interactive use – each user feels as if he/she has the entire machine (at least at at night) – tries to optimize response time – based on time-slicing —dividing available CPU time equally among the users – permits interactive work; participation of users in the execution process – MIT Multics system was first large timesharing system (mid-late 1960s) – requires periodic clock interrupts • Distributed operating systems – facilitate use of geographically distributed resources – supports communication between parts of a job or different jobs – sharing of distributed resources, hardware and software – permits parallelism, but speedup is not necessarily the main objective – not covered in this course—check out Distributed Systems course • Characteristics of current OS’es: – Large  Millions of lines source code  100-10,000 person-years – Complex  asynchronous  concurrent/parallel  abundance of hardware platforms with different idiosyncrasies  conflicting needs of different application programs and users  performance and dependability are crucial What we’ll cover in this course Operating Systems 5 • Process management – Threads and processes – Synchronization – Multiprogramming – CPU Scheduling – Deadlock • Memory management – Dynamic storage allocation – Sharing main memory – Virtual memory • I/O management – File storage management – Naming – Concurrency – Performance • Virtual machines • Protection and Security • Network Communication