Overview of Operating Systems

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interrupt/system calls OS Structures and basic components Ø Process/memory/IO device managers Basic design approaches Ø Monolithic/layered/microkernel/virtual machine etc.

1 Lecture Outline Overview of Operating Systems Instructor: Dr. Tongping Liu Operating System: what is it? Evolution of Computer Systems and OS Concepts Different types/variations of Systems/OS Ø Parallel/distributed/real-time/embedded OS etc. OS as a resource manager Ø How does OS provide service? interrupt/system calls OS Structures and basic components Ø Process/memory/IO device managers Basic design approaches Ø Monolithic/layered/microkernel/virtual machine etc. 1 2 Lecture Outline Operating System: what is it? Evolution of Computer Systems and OS Concepts Different types/variations of Systems/OS Ø Parallel/distributed/real-time/embedded OS etc. OS as a resource manager Ø How does OS provide service? interrupt/system calls OS Structures and basic components Ø Process/memory/IO device managers Basic design approaches Ø Monolithic/layered/microkernel/virtual machine etc. First Computer: ENIAC in 1940s Big: 27 tons, 680 ft^2, and use 150kW Slow: tens instructions/per second Limited functions: addition/multiplication Hard to use: button switch or punching card I/O 3 4 1

First Computer: ENIAC (cont.) Got a problem with a program?

jobs Ø Process one by one Ø I/O devices are still slow? Debug the program!

Control Unit Arithmetic/Logic Unit Output Device Since then computers more or less based on the

2 First Computer: ENIAC (cont.) Got a problem with a program? à You are in trouble J Another Problem of ENIAC Earlier computers, e.g. ENIAC, were hard-wired to do one task. If the computer had to perform a different task, it had to be rewired, which was a tedious process. Process one job at a time Ø A slow speed Ø CPU time is precious Batch systems Ø Read in more jobs Ø Process one by one Ø I/O devices are still slow? Debug the program! 5 6 Von Neumann Architecture (1945) Classic Computer Design Input Device Central Processing Unit Control Unit Arithmetic/Logic Unit Output Device Since then computers more or less based on the same basic design, the Von Neumann Architecture! With a stored-program computer, a general purpose computer could be built to run different programs. Store data and program Memory Unit Execute program Do arithmetic/logic operations requested by program IO: communicate with "outside world 7 8 CMPUT101 Introduction to Computing 2

I/O devices display, keyboard, mouse and printers Today, desktop computers may run several different types of operating systems (Windows, MacOS, Linux) Parallel High-Performance Systems Goals: Ø

3 Desktop Systems: 1980s Personal computers dedicated to a single user; Objective: User convenience and responsiveness. Ø Individuals have sole use of computers Ø A single user may not need advanced features of mainframe OS (maximize utilization, protection). I/O devices display, keyboard, mouse and printers Today, desktop computers may run several different types of operating systems (Windows, MacOS, Linux) Parallel High-Performance Systems Goals: Ø Increased performance/throughput Ø Increased reliability, e.g. fault tolerance Multiprocessor systems: more than one CPUs Ø Tightly coupled system processors share memory, bus, IO, and clock; communication usually takes place through the shared memory Symmetric multiprocessing (SMP) vs. asymmetric Ø SMP: each processor runs an identical copy of the operating system, and all processors are peers Ø Asymmetric: master-slave 9 10 Modern Computer Hardware Organization Big Picture of Computer Systems User 1! User 2! User 3!...! User n! Compiler! app.! Text editor! Database system! System and Application Programs! von Neumann Architecture: stored program I/O devices Operating System! Hardware (CPU, MEM)!

4 Why do you need an OS? Definition of Operating System + OS (Windows) $300 $200 Do I have to buy the OS? Yes: you should have an OS to employ a modern computer Ø Otherwise, a set of silicon circuits do nothing good for you! OS provides user-friendly interfaces for using computers 13 A program manages computer hardware and software resources and provides common services for user programs. Different names for OS: Ø Kernel the program running at all times (different from application programs) Ø Control program controls the execution of user programs and operations of I/O devices Ø Resource allocator manages and allocates resources Goals of Operating system Ø Convenience: Make the computer convenient to use. Ø Efficiency: Manage system resources in an efficient manner 14 Lecture Outline Operating System: what is it? Evolution of Computer Systems and OS Concepts Different types/variations of Systems/OS Ø Parallel/distributed/real-time/embedded OS etc. OS as a resource manager Ø How does OS provide service? interrupt/system calls OS Structures and basic components Ø Process/memory/IO device managers Basic design approaches Ø Monolithic/layered/microkernel/virtual machine etc. Multiprogrammed Systems Several jobs run concurrently Ø Job: computing à input à computing à à output Ø Take turns to use CPU and I/O devices But which job uses what and when? Ø Need a manager/supervisor à OS A single program cannot keep busy for CPU and IO, thus wasting resources How to use the hardware (e.g., I/O devices)? Ø Resource manager/interface à OS

Time Sharing Systems Extension of multi-programmed systems Multiple interactive users Ø Allow on-line interaction with users; Ø Response time for each user should be short CPU is multiplexed among

with 10 ms time quantum Example systems: IBM 704 and 7090 Multiprogramming vs.

5 Time Sharing Systems Extension of multi-programmed systems Multiple interactive users Ø Allow on-line interaction with users; Ø Response time for each user should be short CPU is multiplexed among several jobs of several users that are kept in memory Ø CPU is allocated to jobs in Round-Robin manner Ø All active users must have a fair share of the CPU time: e.g. with 10 ms time quantum Example systems: IBM 704 and 7090 Multiprogramming vs. Time-Sharing Multiprogramming is the effective utilization of CPU time, by allowing several programs to use the CPU at the same time but time sharing is the sharing of a computing facility by several users that want to use the same facility at the same time Distributed Systems Loosely coupled system each processor has its own local memory, communicating with another one through various communications lines Advantages of distributed systems. Ø Resource sharing Ø Computation speed up load sharing Ø Reliability Ø Communications Peer-to-Peer Computing Systems One type of distributed system" P2P does not distinguish clients and servers" Ø All nodes are considered as peers" Ø Each may act as the client, the server or both" Ø A node must join P2P network" ü Registers its service with the central lookup service on network, or" ü Broadcasts requests for service and responds to requests for service via discovery protocol! Ø Examples include Napster and Gnutella! 19 5

6 Special Purpose Systems A real-time system is used when strict time requirements have been placed on the operation of a processor or the flow of data Ø Hard real-time: critical tasks must be completed on time Ø Soft real-time: no absolute timing guarantees (e.g. besteffort scheduling ); multimedia applications; An embedded system is a component of a more complex system Ø Control of a nuclear plant or Missile guidance Ø Control of home and car appliances (microwave oven, DVD players, car engines, ) Example: VxWorks and ecos; Android and ios Lecture Outline Operating System: what is it? Evolution of Computer Systems and OS Concepts Different types/variations of Systems/OS Ø Parallel/distributed/real-time/embedded OS etc. OS as a resource manager Ø How does OS provide service? interrupt/system calls OS Structures and basic components Ø Process/memory/IO device managers Basic design approaches Ø Monolithic/layered/microkernel/virtual machine etc Example: System-Call Processing. Standard C Library Example C program invoking printf() library call, which calls write() system call" 23 6

. Types of System Calls Examples: Major System Calls in Unix Process control" File management" Device management" Information maintenance" Communications" Protection" " 26 Examples of Windows and

7 . Types of System Calls Examples: Major System Calls in Unix Process control" File management" Device management" Information maintenance" Communications" Protection" " 26 Examples of Windows and Unix System Calls Operation Modes Hardware support (mode bit) to differentiate between at least two modes of operations Ø User mode execution done on behalf of a user Ø Kernel mode (also monitor mode or system mode or privileged mode) executing on behalf of operating system E.g., interrupts: à switches to monitor mode. Interrupt! Privileged instructions can be issued only in kernel mode.! kernel! set user mode! user! 28 7

System call control flow - Linux User applica+on calls a user-level library rou+ne (gettimeofday(), read(), exec(), etc.) Invokes system call through stub, which specifies the system call number.

h: #define NR_getpid 172 SYSCALL( NR_getpid, sys_getpid) This generally causes an interrupt, trapping to kernel Kernel looks up system call number in syscall table, calls appropriate func+on Func+on

8 System call control flow - Linux User applica+on calls a user-level library rou+ne (gettimeofday(), read(), exec(), etc.) Invokes system call through stub, which specifies the system call number. From unistd.h: #define NR_getpid 172 SYSCALL( NR_getpid, sys_getpid) This generally causes an interrupt, trapping to kernel Kernel looks up system call number in syscall table, calls appropriate func+on Func+on executes and returns to interrupt handler, which returns the result to the userspace process System call control flow - Linux The idea is s+ll the same, although code is different 29 4/5/ /5/2012 System Calls System calls provide the services of the operating system to user programs. System calls are the only entry points into the kernel system. Ø Generally available in routines written in C and C++ Ø Certain low-level tasks may be written using assembly language System Calls vs. APIs Application programming interface (API) Ø An application programming interface (API) is (as the name suggests) an interface for your application to use code that does not belong to your application (e.g. a library or a system call). Ø Some APIs might have system calls within them, e.g. read, write. They have side effects outside the scope of a program. Ø Some APIs might not invoke system calls, e.g. memcpy

9 Interrupt An interrupt automatically puts the CPU into some elevated privilege level, and then passes control to the kernel, which determines whether the calling program should be granted the requested service If the service is granted, the kernel executes a specific set of instructions over which the calling program has no direct control, returns the privilege level to that of the calling program, and then returns Definition of Interrupt During normal execution of a computer program, there could be events that can cause the CPU to temporarily halt. Events like this are called interrupts. Ø Hardware interrupts, called as interrupts Ø Software interrupts, called as exceptions or traps System calls vs. (Hardware) Interrupts System call is a call to a subroutine built in to the system, while interrupt is an event that causes the processor to temporarily hold the current execution. Ø system calls are synchronous, while interrupts are not Ø Unlike a system call, an interrupt usually does not have anything to do with the current program. Ø When ever a system call occurs the processor only has to remember where to return to, but in the event of an interrupt, the processor has to remember both the place to return to and the state of the system. Interrupt Mechanisms Save the current process state Interrupt transfers control to the interrupt service routine (ISR) generally through interrupt vector containing the addresses of all the service routines. ISR: Separate segments of code determine what action should be taken for each type of interrupt. Once the interrupt has been serviced by the ISR, the control is returned to the interrupted program

10 Basic Interrupt Processing 1. The interrupt is issued 2. Processor finishes the execution of current instruction 3. Processor signals the acknowledgement of interrupt 4. Processor pushes the program status and PC to control stack 5. Processor loads new PC value via the interrupt vector 6. ISR saves the remainder of the process state information 7. ISR executes 8. ISR restores process states 9. Old states and PC values are restored from the control stack What if another interrupt occurs during interrupt processing? 37 Nesting Interrupts Only some systems support nesting interrupts, some do not. If nesting interrupt is allowed, but with restrictions. The common notion is that a high priority device can interrupt a low priority device, but not vice versa. Ø Programmers may provide the ability to enable and disable these interruptions at different times during program execution. Ø If interruption is disabled, the CPU does not respond to an interrupt signal. Ø After completion of the high-priority devices interrupt service routine, the processor will meet the demand of low priority interrupt devices 38 Classes of Interrupts I/O Interrupts: Generated by an I/O controller, to signal normal completion of an operation or to signal a variety of error conditions Timer Interrupts: Generated by a timer within the processor. This allows the operating system to perform certain functions on a regular basis, like scheduling Hardware Failure Interrupts: Generated by a failure (e.g. power failure or memory parity error). Traps (Software Interrupts): Generated by some condition that occurs as a result of an instruction execution Ø User request for an operating system service (e.g., system calls) Ø Runtime errors Lecture Outline Operating System: what is it? Evolution of Computer Systems and OS Concepts Different types/variations of Systems/OS Ø Parallel/distributed/real-time/embedded OS etc. OS as a resource manager Ø How does OS provide service? interrupt/system calls OS Structures and basic components Ø Process/memory/IO device managers Basic design approaches Ø Monolithic/layered/microkernel/virtual machine etc

11 Components in Operating System Process/thread Management Ø CPU (processors): most precious resource Memory Management Ø Main memory File Management à data /program Secondary-Storage Management à disk I/O System Management à I/O devices Protection and Security à access management I/O Process Management A process is a program in execution (active), Ø Dynamic concept, represented by process control block A process needs resources: execution environment Ø including CPU time, registers, memory, files, and I/O devices to accomplish its task OS provides mechanism to Ø Create/delete processes Ø Run/Suspend/resume processes (scheduling/signal) Ø Process communication and synchronization Ø Deadlock handling I/O devices Main Memory Management File Management The main memory is Ø a large array of words/bytes, each with its own address Ø a volatile storage device that the content is lost when power is off The operating system will Ø Keep track of which parts of memory are currently being used and by whom Ø Decide which processes to load when memory becomes available Ø Allocate and de-allocate memory space as needed A file is a collection of related information (logic unit) Ø Format is defined by its creator. Represent programs (source/object forms) and data Operating system responsibilities Ø File creation and deletion Ø Directory creation and deletion Ø Support of primitives for manipulating files and directories Ø Mapping files onto secondary storage Ø File backup on stable (non-volatile) storage media

12 Secondary-Storage Management The secondary storage backs up main memory and provides additional storage. Most common secondary storage type: disks The operating system is responsible for Ø Free space management Ø Storage allocation Ø Disk scheduling I/O System Management The Operating System will hide the peculiarities of specific I/O hardware from the user. In Unix, the I/O subsystem consists of: Ø A buffering, caching and spooling system Ø A general device-driver interface Ø Drivers for specific hardware devices Interrupt handlers and device drivers are crucial in the design of efficient I/O subsystems Storage Hierarchy Storage systems organized in hierarchy" Ø Speed" Ø Cost" Ø Volatility" Caching copying information into faster storage system; main memory can be viewed as a last cache for secondary storage Caching Important principle, performed at many levels in a computer (in hardware, operating system, software)" Information in use copied from the slower to the faster storage temporarily" Faster storage (cache) will be checked first to determine if information is there" Ø If it is, information is used directly from the cache (fast)" Ø If not, data is copied to cache and used there" Cache smaller than storage being cached" Ø Cache management important design problem" Ø Cache size and replacement policy" " 12

Components in Operating System Process/thread Management Ø CPU (processors): most precious resource Memory Management Ø Main memory File Management à data /program Secondary-Storage Management

interpreter (or shell) Ø Graphical User Interface (GUI) The shell Ø allows users to directly enter commands that are to be performed by the operating system Ø Is usually a system program (not

13 Components in Operating System Process/thread Management Ø CPU (processors): most precious resource Memory Management Ø Main memory File Management à data /program Secondary-Storage Management à disk I/O System Management à I/O devices Protection and Security à access management OS Interface: Shell and GUI For both programmers and end-users Two main interfaces: Ø Command-line interpreter (or shell) Ø Graphical User Interface (GUI) The shell Ø allows users to directly enter commands that are to be performed by the operating system Ø Is usually a system program (not part of the kernel) GUI allows a mouse-based window-and-menu system: click-and-play Some systems allow both (e.g. X-Windows in Unix) I/O devices Bourne Shell Command Interpreter The Mac OS X GUI 13

Lecture Outline Operating System: what is it? Evolution of Computer Systems and OS Concepts Different types/variations of Systems/OS Ø Parallel/distributed/real-time/embedded OS etc.

14 Lecture Outline Operating System: what is it? Evolution of Computer Systems and OS Concepts Different types/variations of Systems/OS Ø Parallel/distributed/real-time/embedded OS etc. OS as a resource manager Ø How does OS provide service? interrupt/system calls OS Structures and basic components Ø Process/memory/IO device managers Basic design approaches Ø Monolithic/layered/microkernel/virtual machine etc. Operating System Design Approaches Simple Structure Ø MS-DOS and original Unix Layered Approach Microkernels Modular Approach Virtual Machines Simple System Structure MS-DOS Structure Some operating systems do not have well-defined structures. Often, they started as simple systems and grew beyond their original scope. MS-DOS written to provide the most functionality in the least space Ø not divided into modules Ø Although MS-DOS has some structures, its interfaces and levels of functionality are not well separated. 55 Problem: applications are able to access drivers 56 14

memory management, and other operating-system functions ü A large number of functions for one level.

15 Original UNIX System Structure Original UNIX System Structure UNIX is limited by hardware functionality, with limited structure. The UNIX OS consists of two separable parts: Ø Application programs Ø The kernel (everything below the system-call interface and above the physical hardware) ü Provides file system, CPU scheduling, memory management, and other operating-system functions ü A large number of functions for one level Layered Approach Microkernel Approach OS functions is divided into a number of layers (levels) Ø The bottom layer (layer 0) is the hardware; Ø the highest (layer N) is the user interface. Ø Functions at one layer only uses functions and services of lower-level layers. Simplifies debugging and system verification? Layered debugging: up from layer 0 Problems? How to define layers? Less efficient 59 Keep the minimal services in kernel (process, memory, communication etc.); moves as much as possible from the kernel into user space Communication takes place between user modules using message passing; Advantage: flexibility and extensibility Ø services can be added, modified and debugged Ø small kernel à fewer bugs Ø protection of services and resources is still maintained 60 15

16 Microkernel Approach (cont.) Modular Approach Modular kernel Ø The kernel includes a set of core components Ø Dynamically links in additional services either during boottime or during run-time Ø Common in modern implementations of Unix such as Linux and Solaris Problems with microkernel approach? Performance decrease due to system function overhead Virtual Machines Virtual Machines (Cont.) Takes the layered approach to its logical conclusion. A virtual machine provides an interface identical to the underlying bare hardware Each user is given its own virtual machine The operating system creates the illusion of multiple processes, each executing on its own processor with its own (virtual) memory Become more popular with multicore systems Linux XP OS X

17 Virtual Machines (Evaluation) The virtual-machine concept provides complete protection (because of complete isolation). This isolation, however, permits no direct sharing of resources. A virtual-machine system is a perfect vehicle for operating-systems research and development. The virtual machine concept is difficult to implement due to the effort required to provide an exact duplicate of the underlying machine Next Lecture Process management Ø SGG Chapters 3 and

Overview of Operating Systems

Lecture Outline Overview of Operating Systems Instructor: Dr. Tongping Liu Thank Dr. Dakai Zhu and Dr. Palden Lama for providing their slides. 1 2 Lecture Outline Von Neumann Architecture 3 This describes