Download Operating Systems: Announcements and Components for CMSC 412, Fall 2004 - Prof. Michael W. and more Study notes Operating Systems in PDF only on Docsity! 1 1 CMSC 412 Fall 2004 Operating Systems Structures Announcements • Project #1 – Posted. Due Friday. • Reading – Chapter 3, 4 2 2 Common System Components • Process Management • Main Memory Management • File Management • I/O System Management • Secondary Storage Management • Networking • Protection System • Command-Interpreter System Process 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. • 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 5 5 Networking • A distributed system is a collection processors that do not share memory or a clock, connected through a communication network. – Communication takes place using a protocol. • Networking-related OS activities – Managing protocol state – Managing states of distributed resources (e.g. remote filesystem) Protection 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. 6 6 Command-Interpreter System • 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 Command-Interpreter System • 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. 7 7 Operating System Services • Program execution – Load a program into memory and to run it. • I/O operations • File-system manipulation • Communications – Between local or distributed processes – Either shared memory or message passing. • Error detection and recovery – In the CPU and memory hardware, in I/O devices, or in user programs. Additional OS Functions •Resource allocation •Allocating resources to multiple users or multiple jobs running at the same time. •Accounting •Keep track of and record which users use how much and what kinds of computer resources for account billing or for accumulating usage statistics. •Protection •Controlling all access to system resources. 10 10 Example: OS/2 OS Structure: Hybrid • Layering has problems on its own – May be difficult to communicate information easily – May be inefficient • Hybrid – Use layered, modular approach, but permit “back doors” to improve information flow at the cost of abstraction 11 11 Policy vs. Mechanism • Policy - what to do – users should not be able to read other users files • Mechanism- how to accomplish the goal – file protection properties are checked on open system call • Want to be able to change policy without having to change mechanism – change default file protection • Extreme examples of each: – micro-kernel OS - all mechanism, no policy – MacOS - policy and mechanism bound together Microkernel System Structure • Goal: make the kernel as small as possible. • Communication takes place between user modules using message passing via the kernel. • Benefits: – easier to extend a microkernel – easier to port the OS to new architectures – more reliable and secure (less code running in kernel mode) • Drawback: – More overhead for operation Windows NT Client-Server
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