Operating System - Lecture 2

Operating-System Structures

Operating system

Provides an environment for the execution of programs.

User

One set of operating system services provides functions that are helpful to the _____

User Interface
Program Execution
I/O Operations
File-system manipulation
Communications
Error Detection
Resource Allocation
Logging
Protection and Security

Operating System Structures:

User Interface

This interface is a window system with a mouse that servers as a pointing device to direct I/O, choose from menus, and make selections and a keyboard to enter text.

Command-Line Interface

Uses text commands and a method for entering them is also another option.

Program Execution

The system must be able to load a program into memory and to run that program.

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. They also need to create and delete them by name, search for a given file, and list file information.

Communications

May be implemented via shared memory or message passing

Shared memory

Two or more processes read and write to a shared section of memory

Message passing

Packets of information in predefined formats are moved between processes by the operating system.

Resource Allocation

When there are multiple processes running at the same time, resources must be allocated to each of them.

Logging

This record keeping may be used for accounting (so that users can be billed) or simply accumulating usage statistics.

Usage statistics

May be a valuable tool for system administrators who wish to reconfigure the system to improve computing services.

Protection and Security

Protection involves ensuring that all access to system resources is controlled.

Command Interpreters
Graphical User Interface
Touch-Screen Interface

User and Operating-System Interface:

Command Interpreters

A special program that is running when a process is initiated or when a user first logs on.

Shells

On systems with multiple command interpreters to choose from, the interpreters are known as _____

Graphical User Interface

Users employ a mouse-based window-and-menu system characterized by a desktop metaphor.

Touch-Screen Interface; gestures

In this interface, users interact by making ______ on the touch screen – for example, pressing and swiping fingers across the screen.

System Calls

Provide an interface to the services made available by an operating system.

Sequence of system calls

Another approach is for the program to ask the user for the names. This is the approach that will be required in an interactive system

Application Programming Interface (API)

Specifies a set of functions that are available to an application programmer, including the parameters that are passed to each function and the return values the programmer can expect.

To compile and run on any system that supports the same API

An application programmer designing a program using an API can expect the program _________

more detailed and more difficult to work with

Actual system calls can often be _________ than the API available to an application programmer.

Run-time Environment

The full suite of software needed to execute applications written in a given programming language, including its compilers or interpreters as well as other software, such as libraries and loaders.

System-Call Interface

Serves as the link to system calls made available by the operating system.

System-Call Interface

Intercepts function calls in the API and invokes the necessary system calls within the operating system.

pass the parameters in registers

The simplest approach to pass parameters to the operating system is to ______

Parameters

These generally stored in a block, or table, in memory, and the address of the block is passed as a _____ in a register.

Process Control
File Management
Device Management
Information Maintenance
Communication
Protection

Types of System Calls

Dump of memory

This is sometimes taken and an error message is generated if a system call is made to terminate the currently running program abnormally, or if the program runs into a problem and causes an error trap.

Debugger

A system program designed to aid the programmer in finding and correcting errors, or bugs–to determine the cause of the problem

Interactive system

The command interpreter simply continues with the next command; it is assumed that the user will issue an appropriate command to respond to any error.

GUI system

A pop-up window here might alert the user to the error and ask for guidance

File Management

Either system call requires the name of the file and perhaps some of the file’s attributes

Device Management

A process may need several resources to execute–main memory, disk drives, access to files, and so on.

Information Maintenance

Many system calls exist simply for the purpose of transferring information between the user program and the operating system

Message-passing model

The communicating process exchange messages with one another to transfer information. Messages can be exchanged between the processes either directly or indirectly through a common mailbox.

Shared-memory model

These processes calls to create and gain access to regions of memory owned by other processes.

Protection

Provides a mechanism for controlling access to the resources provided by a computer system.

File management
Status information
File modification
Programming-language support
Program loading and execution
Communications
Background services

System Services:

System services (system utilities)

It provide a convenient environment for program development and execution. Some of them are simply user interfaces to system calls.

File management

These programs create, delete, copy, rename, print, list, and generally access and manipulate files and directories.

Status information

Some programs simply ask the system for the date, time, amount of available memory or disk space, number of users, or similar status information.

Registry

Used to store and retrieve configuration information.

File modification

Several text editors may be available to create and modify the content of files stored on disk or other storage devices.

Programming-language support

Compilers, assemblers, debuggers, and interpreters for common programming languages are often provided with the operating system or available as separate download.

Program loading and execution

Once a program is assembled or compiled, it must be loaded into memory to be executed.

Communications

These programs provide the mechanism for creating virtual connections among processes, users, and computer systems.

Background services

All general-purpose systems have methods for launching certain system-program processes at boot time.