Chapter 2: Operating-System Structures Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne ©2013 Chapter 2: Operating-System Structures s Operating System Services s User Operating System Interface s System Calls s Types of System Calls s System Programs s Operating System Design and Implementation s Operating System Structure Operating System Concepts – 9th Edition 2.2 Silberschatz, Galvin and Gagne ©2013 Objectives s To describe the services an operating system provides to users, processes, and other systems s To discuss the various ways of structuring an operating system s To explain how operating systems are installed and customized and how they boot Operating System Concepts – 9th Edition 2.3 Silberschatz, Galvin and Gagne ©2013 Operating System Services s Operating systems provide an environment for execution of programs and services to programs and users s One set of operating-system services provides functions that are helpful to the user: q User interface - Almost all operating systems have a user interface (UI)  Varies between Command-Line (CLI), Graphics User Interface (GUI), Batch q 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) Operating System Concepts – 9th Edition 2.4 Silberschatz, Galvin and Gagne ©2013 q I/O operations - A running program may require I/O, which may involve a file or an I/O device q File-system manipulation - The file system is of particular interest Programs need to read and write files and directories, create and delete them, search them, list file Information, permission management q Communications – Processes may exchange information, on the same computer or between computers over a network  Communications may be via shared memory or through message passing (packets moved by the OS) Operating System Concepts – 9th Edition 2.5 Silberschatz, Galvin and Gagne ©2013 q 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 Debugging facilities can greatly enhance the user’s and programmer’s abilities to efficiently use the system Operating System Concepts – 9th Edition 2.6 Silberschatz, Galvin and Gagne ©2013 Operating System Services (Cont.) s Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing q Resource allocation - When multiple users or multiple jobs running concurrently, resources must be allocated to each of them Many types of resources - Some (such as CPU cycles, main memory, and file storage) may have special allocation code, others (such as I/O devices) may have general request and release code q Accounting - To keep track of which users use how much and what kinds of computer resources Operating System Concepts – 9th Edition 2.7 Silberschatz, Galvin and Gagne ©2013 q 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 If a system is to be protected and secure, precautions must be instituted throughout it A chain is only as strong as its weakest link Operating System Concepts – 9th Edition 2.8 Silberschatz, Galvin and Gagne ©2013 A View of Operating System Services Operating System Concepts – 9th Edition 2.9 Silberschatz, Galvin and Gagne ©2013 User Operating System Interface - CLI s CLI or command interpreter allows direct command entry q Sometimes implemented in kernel, sometimes by systems program (Windows, Unix) q Sometimes multiple flavors implemented – shells q Primarily fetches a command from user and executes it  Sometimes commands built-in, sometimes just names of programs – If the latter, adding new features doesn’t require shell modification Operating System Concepts – 9th Edition 2.10 Silberschatz, Galvin and Gagne ©2013 Operating System Structure s General-purpose OS is very large program s Various ways to structure one as follows Operating System Concepts – 9th Edition 2.31 Silberschatz, Galvin and Gagne ©2013 Simple Structure s I.e MS-DOS – written to provide the most functionality in the least space q Not divided into modules q Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated Operating System Concepts – 9th Edition 2.32 Silberschatz, Galvin and Gagne ©2013 UNIX s UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring The UNIX OS consists of two separable parts q Systems programs q 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 Operating System Concepts – 9th Edition 2.33 Silberschatz, Galvin and Gagne ©2013 Traditional UNIX System Structure Beyond simple but not fully layered Operating System Concepts – 9th Edition 2.34 Silberschatz, Galvin and Gagne ©2013 Layered Approach s 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 s With modularity, layers are selected such that each uses functions (operations) and services of only lowerlevel layers Operating System Concepts – 9th Edition 2.35 Silberschatz, Galvin and Gagne ©2013 Microkernel System Structure s Moves as much from the kernel into user space s Mach example of microkernel q Mac OS X kernel (Darwin) partly based on Mach s Communication takes place between user modules using message passing s Benefits: q Easier to extend a microkernel q Easier to port the operating system to new architectures q More reliable (less code is running in kernel mode) q More secure s Detriments: q Performance overhead of user space to kernel space communication Operating System Concepts – 9th Edition 2.36 Silberschatz, Galvin and Gagne ©2013 Microkernel System Structure Application Program File System messages Interprocess Communication Device Driver user mode messages memory managment CPU scheduling kernel mode microkernel hardware Operating System Concepts – 9th Edition 2.37 Silberschatz, Galvin and Gagne ©2013 Modules s Most modern operating systems implement loadable kernel modules q Uses object-oriented approach q Each core component is separate q Each talks to the others over known interfaces q Each is loadable as needed within the kernel s Overall, similar to layers but with more flexible q Linux, Solaris, etc Operating System Concepts – 9th Edition 2.38 Silberschatz, Galvin and Gagne ©2013 Solaris Modular Approach Operating System Concepts – 9th Edition 2.39 Silberschatz, Galvin and Gagne ©2013 Hybrid Systems s Most modern operating systems actually not one pure model q Hybrid combines multiple approaches to address performance, security, usability needs q Linux and Solaris kernels in kernel address space, so monolithic, plus modular for dynamic loading of functionality q Windows mostly monolithic, plus microkernel for different subsystem personalities s Apple Mac OS X hybrid, layered, Aqua UI plus Cocoa programming environment q Below is kernel consisting of Mach microkernel and BSD Unix parts, plus I/O kit and dynamically loadable modules (called kernel extensions) Operating System Concepts – 9th Edition 2.40 Silberschatz, Galvin and Gagne ©2013 Mac OS X Structure graphical user interface Aqua application environments and services Java Cocoa Quicktime BSD kernel environment BSD Mach I/O kit Operating System Concepts – 9th Edition kernel extensions 2.41 Silberschatz, Galvin and Gagne ©2013 iOS s Apple mobile OS for iPhone, iPad q Structured on Mac OS X, added functionality q Does not run OS X applications natively  Also runs on different CPU architecture (ARM vs Intel) q Cocoa Touch Objective-C API for developing apps q Media services layer for graphics, audio, video q Core services provides cloud computing, databases q Core operating system, based on Mac OS X kernel Operating System Concepts – 9th Edition 2.42 Silberschatz, Galvin and Gagne ©2013 Android s Developed by Open Handset Alliance (mostly Google) q Open Source s Similar stack to IOS s Based on Linux kernel but modified q Provides process, memory, device-driver management q Adds power management s Runtime environment includes core set of libraries and Dalvik virtual machine q Apps developed in Java plus Android API  Java class files compiled to Java bytecode then translated to executable than runs in Dalvik VM s Libraries include frameworks for web browser (webkit), database (SQLite), multimedia, smaller libc Operating System Concepts – 9th Edition 2.43 Silberschatz, Galvin and Gagne ©2013 Applications Android Architecture Application Framework Libraries Android runtime SQLite openGL surface manager media framework webkit Core Libraries Dalvik virtual machine libc Linux kernel Operating System Concepts – 9th Edition 2.44 Silberschatz, Galvin and Gagne ©2013 End of Chapter Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne ©2013