Operating-System Structures - Operating Systems - Lecture Slides, Slides of Operating Systems

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Chapter 2: Operating-System Structures

Operating System Services

• 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), Batch

– 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 - The file system is of particular

interest. Obviously, programs need to read and write files

and directories, create and delete them, search them, list

file Information, permission management.

Operating System Services (Cont)

• One set of operating-system services provides functions that are helpful to

the user (Cont):

• 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)

• 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 systemDocsity.com

Operating System Services (Cont)

• Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing - 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 - 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 - 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.

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)
  • Invented at Xerox PARC
• 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 (Java Desktop, KDE)

Bourne Shell Command Interpreter

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) rather than direct system call use

• 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)

• Why use APIs rather than system calls?

(Note that the system-call names used throughout this text

are generic)

Example of System Calls

• System call sequence to copy the contents of

one file to another file

System 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

API – System Call – OS Relationship

System 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 Docsity.com

Types of System Calls

• Process control

• File management

• Device management

• Information maintenance

• Communications

• Protection

OS organization types

• Kernel based systems

• Microkernel-based systems

• Virtual machines

Kernel based systems

• Traditional organization of Unix systems

• Kernel-space

– Sensitive stuff, controlled only by the OS

– Provides the file system, CPU scheduling, memory

management, and other operating-system

functions;

• a large number of functions for one level

– An error in the kernel can crash the OS

• User-space

– Applications programs