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Structure of operating system

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Structure of operating system

  1. 1. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 1 Chapter 3: Operating-System StructuresChapter 3: Operating-System Structures System Components Operating System Services System Calls System Programs System Structure Virtual Machines System Design and Implementation
  2. 2. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 2 Common System ComponentsCommon System Components A system as large and complex as an OS can be created only by partitioning it into smaller pieces Process Management Main Memory Management File Management I/O System Management Secondary Management Networking Protection System Command-Interpreter System
  3. 3. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 3 Process ManagementProcess Management A process is a program in execution. A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its task.  A process is the unit of work in a system The operating system is responsible for the following activities in connection with process management.  Process creation and deletion.  Process suspension and resumption.  Provision of mechanisms for:  process synchronization  process communication
  4. 4. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 4 Main-Memory ManagementMain-Memory Management Memory is a large array of words or bytes, each with its own address. It is a repository of quickly accessible data shared by the CPU and I/O devices.  The CPU reads instructions from main memory (MM) during the instruction-fetch cycle and both reads and writes data from MM during the data-fetch cycle Main memory is a volatile storage device. It loses its contents in the case of system failure. To improve both CPU utilization and response speed, several programs are kept in memory The following are some of the activities in connections with memory management that are handled by the operating system :  Keep track of which parts of memory are currently being used and by whom.  Decide which processes to load when memory space becomes available.  Allocate and deallocate memory space as needed.
  5. 5. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 5 File ManagementFile Management A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data. The operating system is responsible for the following activities in connections with file management:  File creation and deletion.  Directory creation and deletion.  Support of primitives for manipulating files and directories.  Mapping files onto secondary storage.  File backup on stable (nonvolatile) storage media.
  6. 6. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 6 I/O System ManagementI/O System Management Hide the peculiarities of specific hardware devices from the user The I/O system consists of:  A memory management component that includes buffering, caching and spooling  A general device-driver interface  Drivers for specific hardware devices
  7. 7. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 7 Secondary-Storage ManagementSecondary-Storage Management Since main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory. Most modern computer systems use disks as the principle on-line storage medium, for both programs and data. Because secondary storage is used frequently, it must be used efficiently or else it will become a processing bottleneck The operating system is responsible for the following activities in connection with disk management:  Free space management  Storage allocation  Disk scheduling
  8. 8. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 8 Networking (Distributed Systems)Networking (Distributed Systems) A distributed system is a collection processors that do not share memory or a clock. Each processor has its own local memory. The processors in the system are connected through a communication network. Communication takes place using a protocol. A distributed system provides user access to various system resources. Access to a shared resource allows:  Computation speed-up  Increased data availability  Enhanced reliability
  9. 9. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 9 Protection SystemProtection System Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources. The protection mechanism must:  distinguish between authorized and unauthorized usage.  specify the controls to be imposed.  provide a means of enforcement.
  10. 10. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 10 Command-Interpreter SystemCommand-Interpreter System Serves as the interface between the user and the OS  User friendly, mouse based windows environment in the Macintosh and in Microsoft Windows  In MS-DOS and UNIX, commands are typed on a keyboard and displayed on a screen or printing terminal with the Enter or Return key indicating that a command is complete and ready to be executed Many commands are given to the operating system by control statements which deal with:  process creation and management  I/O handling  secondary-storage management  main-memory management  file-system access  protection  networking
  11. 11. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 11 Command-Interpreter System (Cont.)Command-Interpreter System (Cont.) The program that reads and interprets control statements is called variously:  command-line interpreter  shell (in UNIX) Its function is to get and execute the next command statement.
  12. 12. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 12 System CallsSystem Calls System calls provide the interface between a running program and the operating system.  For example – open input file, create output file, print message to console, terminate with error or normally  Generally available as routines written in C and C++  Certain low-level tasks (direct hardware access) may be written in assembly-language Mostly accessed by programs via a high-level Application Program Interface (API) rather than direct system call use  Provides portability (underlying hardware handled by OS)  Hides the detail from the programmer Three most common APIs are Win32 API for Windows, POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM)
  13. 13. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 13 Example of System CallsExample of System Calls System call sequence to copy the contents of one file to another file
  14. 14. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 14 Example of Standard APIExample of Standard API Consider the ReadFile() function in the Win32 API—a function for reading from a file A description of the parameters passed to ReadFile()  HANDLE file—the file to be read  LPVOID buffer—a buffer where the data will be read into and written from  DWORD bytesToRead—the number of bytes to be read into the buffer  LPDWORD bytesRead—the number of bytes read during the last read  LPOVERLAPPED ovl—indicates if overlapped I/O is being used
  15. 15. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 15 System Call ImplementationSystem Call Implementation Typically, a number associated with each system call  System-call interface maintains a table indexed according to these numbers The system call interface invokes intended system call in OS kernel and returns status of the system call and any return values The caller need know nothing about how the system call is implemented  Just needs to obey API and understand what OS will do as a result call  Most details of OS interface hidden from programmer by API  Managed by run-time support library (set of functions built into libraries included with compiler)
  16. 16. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 16 API – System Call – OS RelationshipAPI – System Call – OS Relationship
  17. 17. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 17 Standard C Library ExampleStandard C Library Example C program invoking printf() library call, which calls write() system call
  18. 18. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 18 System Call Parameter PassingSystem Call Parameter Passing Often, more information is required than simply identity of desired system call  Exact type and amount of information vary according to OS and call Three general methods used to pass parameters to the OS  Simplest: pass the parameters in registers  In some cases, may be more parameters than registers  Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register  This approach taken by Linux and Solaris  Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system  Block and stack methods do not limit the number or length of parameters being passed
  19. 19. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 19 Passing Parameters as a TablePassing Parameters as a Table
  20. 20. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 20 Types of System CallsTypes of System Calls Process control  end, abort, load, execute, allocate/free memory File management  Create/delete file, open, close, read, write Device management  Request/release device, read, write Information maintenance  Get/set date or time, get process, get/set system data Communications  Send/receive message, create/delete comm link
  21. 21. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 21 UNIX System CallsUNIX System Calls
  22. 22. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 22 MS-DOS ExecutionMS-DOS Execution MS-DOS is an example of a single tasking system  Has command interpreter (shell) which is invoked at startup time  Loads the program into memory, writing over most of the shell to give the program as much memory as possible  The instruction pointer is set to the first instruction of the program and it begins running  Programs either terminates normally or abends providing a return code that is saved in system memory  The resident portion of the shell resumes execution, reloads remainder of the shell and makes the previous error code available to the user or next program
  23. 23. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 23 MS-DOS ExecutionMS-DOS Execution At System Start-up Running a Program
  24. 24. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 24 UNIX Running Multiple ProgramsUNIX Running Multiple Programs FreeBSD is a multitasking system  Shell accepts a command to run a program but, unlike MS- DOS, continues to run while the other program is executing  To start a new process, the shell executes a fork system call which enables another program to be loaded into memory and executed  A process can run in the “background” but then it can not accept input from the keyboard (as it is dedicated to the shell) but can read and writes files  The shell again waits for further commands – run another program, monitor the progress of the running processes, change priorities, etc.  When a process terminates it issues an exit system call returning a status code
  25. 25. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 25 UNIX Running Multiple ProgramsUNIX Running Multiple Programs
  26. 26. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 26 System ProgramsSystem Programs System programs provide a convenient environment for program development and execution. The can be divided into:  File manipulation  Status information (date,time, # of users, free memory etc.)  File modification (text editors)  Programming language support (compilers, assemblers, etc)  Program loading and execution (loaders, linkage editors)  Communications (create virtual connections among processes, users and different computer systems)  System utilities or application programs (web browsers, word processing, spreadsheets etc) Most users’ view of the operating system is defined by system programs, not the actual system calls.
  27. 27. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 27 OS Design ImplementationOS Design Implementation Mechanisms determine how to do something, policies decide what will be done. The separation of policy from mechanism is a very important principle in designing OSs  It allows maximum flexibility if policy decisions are to be changed later.  The mechanism that implements the policy to give priority to I/O intensive processes over CPU intensive processes should be written in a general way so that if the policy is changed no or minimal change to the mechanism would be required  The timer provides is a mechanism providing CPU protection. How long it runs for a particular user is a policy decision.
  28. 28. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 28 System ImplementationSystem Implementation Traditionally written in assembly language, operating systems can now be written in higher-level languages. Code written in a high-level language:  can be written faster.  is more compact.  is easier to understand and debug. Opponents to OSs written high-level language claim slower performance and increased storage Proponents argue:  Modern compilers can produce highly optimized code  Todays OSs run on highly complex hardware which can overwhelm the programmer with details  Better data structures and algorithms will truly improve the performance of OSs  Only a small amount of code is critical to high performance – bottlenecks can be replaced with assembler code later on An operating system is far easier to port (move to some other hardware) if it is written in a high-level language.
  29. 29. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 29 Operating System StructureOperating System Structure MS-DOS – written to provide the most functionality in the least space  Not well divided into modules  Designed without realizing it was going to become so popular  Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated  Vulnerable to system crashes when a user program fails  Written for Intel 8088 which had no dual mode or hardware protection MS-DOS layer structureMS-DOS layer structure
  30. 30. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 30 Operating System StructureOperating System Structure UNIX – the original UNIX operating system had limited structuring due to limited hardware functionality. The UNIX OS consists of two separable parts.  Systems programs  The kernel – series of interfaces and device drivers  Consists of everything below the system-call interface and above the physical hardware  Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level.  All this functionality in one level makes UNIX difficult to enhance – difficult to determine impact of change in one part of the kernel on other parts
  31. 31. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 31 UNIX System StructureUNIX System Structure kernel
  32. 32. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 32 Layered ApproachLayered 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.  Simplifies debugging and system verification – each layer only uses those below it, so by testing from bottom up, you isolate errors to the layer being tested  Requires careful definition of layers  Less efficient as each layer adds overhead to the system increasing overall time for a system call to execute An operating system layerAn operating system layer
  33. 33. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 33 Layered ApproachLayered Approach These limitations have led to the design of OSs with fewer layers each with more functionality Provides most of the advantages of modularized code while avoiding the difficulties of layer definition and interaction OS/2, a descendent of MS-DOS, adds multitasking and dual-mode operation  Designed in a more layered approach than MS-DOS  Direct access to low-level facilities is not allowed; this gives the OS more control over the hardware and more knowledge of which resources each user program is using The first release of Windows NT had a highly layered approach but it delivered low performance compared to Windows 95  NT 4.0 addressed that problem in part by moving layers from user space to kernel space and more closely integrating them
  34. 34. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 34 OS/2 Layer StructureOS/2 Layer Structure
  35. 35. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 35 Microkernel System StructureMicrokernel System Structure In the mid 1980s, researchers at Carnegie Mellon developed the Mach microkernel OS Moves nonessential components from the kernel into “user” space resulting in a smaller kernel Main function of the microkernel is to provide a communication facility between the client program and various services that are also running in user space  Communication takes place between user modules using message passing. Benefits:  easier to extend a microkernel  all new services are added to user space  easier to port the operating system to new architectures  more reliable and secure  less code is running in kernel mode Apple MacOS X Server OS is based on the Mach kernel  maps system calls into messages to the appropriate user-level services
  36. 36. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 36 ModulesModules Best, current technology for OS design involves using object oriented programming techniques to create a modular kernel Kernel dynamically links in additional services either during boot time or run time  Uses dynamically loadable modules (Solaris, Linux, Mac OS X)  Kernel provides core services and others implemented dynamically  Similar but more efficient than microkernel design because modules do not need to invoke message passing in order to communicate
  37. 37. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 37 Solaris loadable modulesSolaris loadable modules
  38. 38. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 38 Virtual MachinesVirtual Machines A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware. A virtual machine not provide any additional functionality but provides an interface identical to the underlying bare hardware. Each process is provided with a (virtual) copy of the underlying computer The operating system creates the illusion that a process has its own processor with its own (virtual) memory. The resources of the physical computer are shared to create the virtual machines.  CPU scheduling can create the appearance that users have their own processor.  Spooling and a file system can provide virtual card readers and virtual line printers.  A normal user time-sharing terminal serves as the virtual machine operator’s console.
  39. 39. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 39 System ModelsSystem Models Non-virtual Machine Virtual Machine
  40. 40. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 40 Virtual MachinesVirtual Machines The virtual-machine concept provides complete protection of system resources since each virtual machine is isolated from all other virtual machines. This isolation, however, permits no direct sharing of resources. A virtual-machine system is a perfect vehicle for operating- systems research and development. System development is done on the virtual machine, instead of on a physical machine and so does not disrupt normal system operation. The virtual machine concept is difficult to implement due to the effort required to provide an exact duplicate to the underlying machine Virtual machines are a means to solve system compatibility problems  Windows applications to run on Linux-based computers  Intel instructions are translated into the native instruction set
  41. 41. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 41 Java Virtual MachineJava Virtual Machine A platform is the hardware or software environment in which a program runs. Some of the most popular platforms are Windows 2000, Linux, Solaris, and MacOS. Most platforms can be described as a combination of the operating system and hardware. The Java platform differs from most other platforms in that it's a software-only platform that runs on top of other hardware- based platforms. Compiled Java programs are platform-neutral bytecodes executed by a Java Virtual Machine (JVM). The JVM is specific for each system and it abstracts the system in a standard way to the Java program eliminating code changes when ported from one platform to another
  42. 42. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 42 Communication ModelsCommunication Models Communication between processes may take place using either message passing or shared memory. Message passing  Information is exchanged through an interprocess communication facility provided by the OS  Computers have host names, processes have process names for identification purposes  Useful when smaller number of data need to be exchanged  Easier to implement than shared memory Shared memory  Processes use map memory system calls to gain access to regions of memory owned by other processes  Allows maximum speed and convenience of communication  Problems arise in the area of protection and synchronization
  43. 43. Operating System Concepts / Silberschatz / Ch 3 Oper Sys StrcuturesSlide 43 Communication ModelsCommunication Models Message Passing Shared Memory

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