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 Program that runs on a computer  Manages hardware resources  Allows for execution of programs  Acts as an intermediary between  Programs  The user  The physical machine  Provides services to  User  Programs run by the user (and OS) 3Operating Systems

4 NASA plans to launch three smartphone nanosatellites later this year. Above is the PhoneSat 1.0 during a high-altitude balloon test. (NASA) iOS (previously iPhone OS) is a mobile operating system developed and distributed by Apple Inc. Originally released in 2007 for the iPhone and iPod Touch, it has been extended to support other Apple devices such as the iPad and Apple TV.

Operating Systems5 Windows Bit March 92 Windows Bit August 95 Windows 7 64 Bit July 2009

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 File operations  Create, modify, read, and delete files  Process control  Schedules and manages program execution  Users accounts, permissions, and logins  Ensures users login and can only access allowed resources  Hardware  Manages access to hardware resources  Examples:  Sending a document to a printer  Send/receive data to/from a network card 7Operating Systems

1. Graphical User Interface (GUI)  Allows user to interact with the system  User actions translated into API calls (or shell commands) 2. Shell  Command-line interface to the OS  Can be used by both users and programs 3. Application Programming Interface (API)  Allows programs to interact with the OS “system calls” 8Operating Systems

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Operating Systems11 All software has to request other software to do some things for it. To accomplish this, the asking program uses a set of standardized requests, called application programming interfaces (API), that have been defined for the program being called upon.

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 Method for storing, retrieving, and organizing arbitrary data  Hierarchical structure  Usually a tree  Every file and folder has a place in the hierarchy  Path: human-readable representation of the location of a folder/file within the hierarchy  C:\Program Files (x86)\Frhed\Frhed.exe  Manages  Local storage  Hard drives  Removable storage  USB drives, SD cards, optical discs  Network storage 13Operating Systems

 OS provides tools for managing the file system  Drive naming  Drive letters (Windows)  Separate tree for each drive letter  Mount points (UNIX)  All drives mounted into a single tree  Shell commands  Windows: dir, cd (or chdir), move, copy, md (or mkdir)  UNIX: ls, cd, pwd, mv, cp, mkdir  Command reference  ictionary.html ictionary.html 14Operating Systems

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 Consist of  Command name  Name of the program to execute  Some commands are built-in to the shell  Zero or more arguments  Information the command needs to operate  Spaces normally separate arguments  Use “ ”s to make arguments with spaces a single argument  Zero or more options  Modify the operation of the command  Prefixed with a / or – character in Windows  - character in UNIX move /-Y C:\Users\billy\Downloads\vacation.jpg photos\archive\vacation.jpg \ \ \ \ \ \--- option \--- argument \--- argument \ \--- command name Operating Systems16

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Shell Exercises

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 A program is a file containing instructions for the CPU to execute  Process: an instance of a computer program that is being executed  A running instance of a program is called a process  Process executed by a user are “owned” by that user  The same program can execute more than once simultaneously  Each instance of the program is a separate process  Start “Task Manager” to see process ( which are your running programs ) 20Operating Systems

 OS manages which users are authorized to access the system  Users identified by a username / login ID  OS handles authenticating users  Passwords, biometrics  OS can retain user information in a profile  Save settings and data across login sessions 21Operating Systems

 Files and folders created on a system are “owned” by the creating user  Each file/folder can have only one owner  Owner (generally) has unlimited access to the file/folder  A process can only manipulate a file if the process owner and file owner are the same  A process launched by m cannot access a folder belonging to m Operating Systems

 Control access to resources via access control lists (ACLs)  List of permissions attached to an object  Object can be a file, folder, hardware resource, etc.  Permissions specify allowed actions  Read, write, modify, delete, etc.  Users can be placed into user groups  Permissions assigned to group  Simplifies management  Superuser  Generally one account on system with unlimited rights  UNIX – root  Windows – Administrator  Users can be given superuser privileges  Must be given by a user with equivalent (or higher) privileges  Allows users to execute programs with elevated privileges 23Operating Systems

 Permissions can allow processes owned by one user to access resources owned by another user  Files/folders  Assign users permission to read, write, modify, execute, etc.  Hardware resources  Control which users can access system hardware  Send files to printer  Connect to a network  OS resources  Control which users can  Make changes to system configuration  Add / modify / delete users and groups  Change permissions 24Operating Systems

 OS manages access to installed hardware devices  Device drivers – allow programs to interact with hardware devices  Example: Windows network connections  Each network device requires specific drivers  Drivers specify how OS sends/receives data to/from that specific network device  Programs requiring network access can interface with any network connection in the same manner  OS determines how to interface with specific device 25Operating Systems

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