Chapter 3

 Manage the computer’s resources ◦ CPU ◦ Memory ◦ Disk drives ◦ Printers  Establish a user interface  Execute and provide services for applications software  Carries out all input and output operation

 Definition: Computer hardware and operating system software that dictate what other software can run  Wintel Intel-based PC running Microsoft Windows

 Facilitates communication between the user and the operating system  Two forms ◦ Command line  Text-based  Key commands  Examples: MS-DOS, Unix ◦ Graphical user interface (GUI)  Visual images  Menus  Examples: Windows, Mac OS, Linux

 Command-line interface  Prompt – system is waiting for you to do something  Key a command  Not user-friendly

 Graphical user interface  Eases access to the OS  Most new computers come with Windows already installed

 On-screen pictures ◦ Icons ◦ Menus  Pull down  Pop up ◦ Click to activate a command or function  Fast  Easy  Intuitive

 Home/consumer market ◦ Windows 95 ◦ Windows 98 ◦ Windows Millennium Edition (ME)  Corporate market ◦ Windows NT ◦ Windows 2000  Windows XP  Windows Vista  Windows 7  Windows 8

 First commercially successful GUI (1984)  Served as a model to other GUI systems

 Supports ◦ Multi-user ◦ Time-sharing  Character-based system  Command-line interface  Runs on various processors and many types of computers  Primary OS used on Internet servers

 UNIX-like OS  Open-source software ◦ Download it free ◦ Make changes ◦ Distribute copies ◦ Restriction – any changes must be freely available to the public  PC Setup ◦ PC comes with Windows installed ◦ Install LINUX in a dual-boot configuration

 Windows 8 is a personal computer operating system developed by Microsoft  Development of Windows 8 started before the release of its predecessor, Windows 7, in 2009  Released for general availability on October 26, 2012

 Windows 8 introduced major changes to the operating system's platform  Touch capable user interface to improve its user experience on tablets  Competing with mobile operating systems, including Android and iOS

 New security features in Windows 8 include two new authentication methods tailored towards touchscreens ◦ PINs and picture passwords ◦ Windows Defender  New features and functionality in Windows 8 include a faster startup  Windows 8 also adds native support for USB 3.0 devices

 Resource – hardware or software that is needed to complete a task  Resource Allocation – assigning computer resources to certain programs  Resource De-allocation – releasing resources when a task is complete

 One CPU ◦ Multiprogramming  More than one CPU ◦ Multiprocessing – multiple CPUs can run several programs simultaneously

 Program must be in memory to be executed  Problems ◦ Programs compete for space ◦ May have a very large program ◦ Memory space for each program must not overlap

 The process of providing separate memory space to programs  Memory Protection keeps one program from interfering with another

Partitions or regions Foreground and background Virtual storage (virtual memory)

 Divide memory into sections  The partition must accommodate the largest possible program  Problem ◦ May cause wasted memory space

 Programs are placed in either Foreground or Background  Programs in Foreground have priority for CPU time  While performing read / write operations for the Foreground program, the CPU gives time to a program in Background  Programs are placed in a holding queue while waiting to run

Uses concept of Paging  Divide the program into equal-size pieces (pages)  Store each piece in equal-size memory spaces (page frames)  Typical size is 2KB or 4KB  Create an index to each page and store in a Page Table

Paging Process  A portion of the program is placed in memory  The remainder is on disk  Sections on disk will be brought into memory as needed (one page at a time)

 Problem -- Thrashing ◦ Too large a portion of CPU time is spent locating the correct page and bringing it into memory  Solution ◦ Run fewer programs concurrently ◦ Add memory