Lecture 2- Chapter 2_Operating System Structures_32d5a35a5fee92dbb78fb8526970742c.pdf

Operating System CS204 Dr. Ahmed Moawad 1 Lecture 2 2 Chapter 2: Operating System Structures 3  Agenda Operating System Services User Operating System Interface System Calls Types of System Calls Sys...

Operating System CS204 Dr. Ahmed Moawad 1 Lecture 2 2 Chapter 2: Operating System Structures 3  Agenda Operating System Services User Operating System Interface System Calls Types of System Calls System Programs Operating System Design and Implementation Operating System Structure Operating System Debugging System Boot 4  Objectives To describe the services an operating system provides to users, processes, and other systems. To know system calls and their types. To discuss the various ways of structuring an operating system. 5  Operating System Services Operating systems provide an environment for execution of programs and services to programs and users. One set of operating-system services provides functions that are helpful to the user: User interface - Almost all operating systems have a user interface (UI). ✓ Varies between Command-Line (CLI), Graphics User Interface (GUI), Touch User Interface. Program execution - The system must be able to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error). I/O operations - A running program may require I/O, which may involve a file or an I/O device. File-system manipulation - Programs need to read and write files and directories, create and delete them, search them, list file Information, permission management. 6  Operating System Services (Cont.) Communications – Processes may exchange information, on the same computer or between computers over a network. Error detection – OS needs to be constantly aware of possible errors. ✓May occur in the CPU and memory hardware, in I/O devices, in user program. ✓For each type of error, OS should take the appropriate action to ensure correct and consistent computing. Resource allocation - When multiple users or multiple jobs running concurrently, resources must be allocated to each of them. 7  Operating System Services (Cont.) Accounting - To keep track of which users use how much and what kinds of computer resources. Protection and security - The owners of information stored in a multiuser or networked computer system may want to control use of that information, concurrent processes should not interfere with each other. ✓Protection involves ensuring that all access to system resources is controlled. ✓Security of the system from outsiders requires user authentication, extends to defending external I/O devices from invalid access attempts. 8 A View of Operating System Services 9  User Operating System Interface - CLI Command Line Interface (CLI) or command interpreter allows direct command entry. Primarily fetches a command from user and executes it. Sometimes implemented in kernel, sometimes by systems program. Sometimes commands built-in, sometimes just names of programs. 10 User Operating System Interface - CLI 11  User Operating System Interface - GUI User-friendly desktop metaphor interface. Usually mouse, keyboard, and monitor. Icons represent files, programs, actions, etc. Various mouse buttons over objects in the interface cause various actions (provide information, options, execute function, open directory (known as a folder). Many systems now include both CLI and GUI interfaces. Microsoft Windows is GUI with CLI “command” shell. Apple Mac OS X as “Aqua” GUI interface with UNIX kernel underneath and shells available. Solaris is CLI with optional GUI interfaces. 12 User Operating System Interface - GUI 13 Bourne Shell Command Interpreter 14 The MAC OS GUI 15  User Operating System Interface – Touch Screen Interface Touchscreen devices require new interfaces. Mouse not possible or not desired. Actions and selection based on gestures. Virtual keyboard for text entry. Voice commands. 16  System Calls Programming interface to the services provided by the OS. Typically written in a high-level language (C or C++). Mostly accessed by programs via a high-level Application Program Interface (API). The most common APIs are Win32 API for Windows and POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X). 17  Example of System Calls System call sequence to copy the contents of one file to another file. 18  Example 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 bytes To Read—the number of bytes to be read into the buffer. LPDWORD bytes Read—the number of bytes read during the last read. 19 LPOVERLAPPED ovl—indicates if overlapped I/O is being used.  System Call Implementation Typically, a number associated with each system call. System-call interface maintains a table indexed according to these numbers. 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. 20 API – System Call – OS Relationship 21  Standard C Library Example C program invoking printf() library call, which calls write() system call 22  System Call Parameter Passing 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. 23  Types of System Calls Process control End, abort Load, execute Create process, terminate process Get process attributes, set process attributes Wait for time Wait event, signal event Allocate and free memory File management Create file, delete file Open, close file Read, write, reposition 24 Get and set file attributes  Types of System Calls Device management Request device, release device Read, write, reposition Get device attributes, set device attributes Logically attach or detach devices Information maintenance Get time or date, set time or date Get system data, set system data 25 Get and set process, file, or device attributes  Types of System Calls Communications Create, delete communication connection Send, receive messages Transfer status information attach and detach remote devices Protection Control access to resources Get and set permissions 26 Allow and deny user access Examples of Windows and Unix System Calls 27  System Programs System programs provide a convenient environment for program development and execution. They can be divided into: File manipulation Status information File modification Programming language support Program loading and execution Communications Application programs 28  System Programs Provide a convenient environment for program development and execution. File manipulation - Create, delete, copy, rename, print, dump, list, and generally manipulate files and directories. Status information Some ask the system for info - date, time, amount of available memory, disk space, number of users. Others provide detailed performance, logging, and debugging information. Typically, these programs format and print the output to the terminal or other output devices. 29  System Programs File modification Text editors to modify files. Special commands to search contents of files or perform transformations of the text. Programming-language support - Compilers, assemblers, debuggers and interpreters sometimes provided. Communications - Provide the mechanism for creating virtual connections among processes, users, and computer systems. Allow users to send messages to one another’s screens, browse web pages, send electronic-mail messages, log in remotely, transfer files from one machine to another. 30  System Programs Background services Launch at boot time. ❖Some for system startup, then terminate. ❖Some from system boot to shutdown Application programs Not related to the system. Run by users Not typically considered part of OS. 31  Operating System Design and Implementation Design and Implementation of OS not “solvable”, but some approaches have proven successful. Internal structure of different Operating Systems can vary widely. Start by defining goals and specifications. Affected by choice of hardware, type of system. User goals and System goals. User goals – operating system should be convenient to use, easy to learn, reliable, safe, and fast. System goals – operating system should be easy to design, implement, and maintain, 32 as well as flexible, reliable, error-free, and efficient.  Operating System Design and Implementation Important principle to separate Policy: What will be done? Mechanism: How to do it? Mechanisms determine how to do something; policies decide what will be done. The separation of policy from mechanism is a very important principle, 33 it allows maximum flexibility if policy decisions are to be changed later.  Simple Structure MS-DOS – written to provide the most functionality in the least space. Not divided into modules. Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated. 34  UNIX UNIX – the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts: Systems programs The kernel ❖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. 35 Traditional UNIX System Structure 36  Layered Operating System 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. 37  Microkernel System Structure Microkernel System Structure Moves as much from the kernel into user space. Mach example of micro kernel. Mac OS X kernel partly based on Mach. 38  Operating-System Debugging Debugging is finding and fixing errors, or bugs. OS generate log files containing error information. Failure of an application can generate core dump file capturing memory of the process. Operating system failure can generate crash dump file containing kernel memory. 39  System Boot Operating system must be made available to hardware so hardware can start it. Small piece of code – bootstrap loader, locates the kernel, loads it into memory, and starts it. When power initialized on system, execution starts at a fixed memory location. 40 Thank You 41