©Brooks/Cole, 2003 Chapter 7 Operating Systems Dr. Barnawi

©Brooks/Cole, 2003 Figure 7-1 Computer System Control access to hardware by user Use computer hardware to resolve problems

©Brooks/Cole, 2003 O.S. DEFINITION 7.1

©Brooks/Cole, 2003 Definition of Operating System An operating system is an interface between the hardware and programs or humans An operating system is a program that facilitates the execution of other programs. An operating system is a general manager supervising the activity of computer’s components. Operating System design goals Efficient use of hardware. Easy to use resources

©Brooks/Cole, 2003 O.S. EVOLUTION 7.2 Dr. Barnawi

©Brooks/Cole, Batch Systems Each program to be executed is called a job. A programmer sends a job request along with punched cards for the program and the data. Programmer had no interaction with the system. If the program was successful, the result was sent to the programmer, if not a printout of error was sent. Operating systems only ensured that all of the resources were transferred from one job to the next

©Brooks/Cole, Time Sharing Systems Multiprogramming was introduced to hold several jobs in memory. Multiprogramming system only assign resources to a job when it is available. Multiprogramming brought the idea of time sharing where resources are shared between different jobs. Multiprogramming requires a more complex OS. The OS has to do scheduling and decide which program should use the resources and when. Dr. Barnawi

©Brooks/Cole, Personal System Introduced for personal computers. Examples Disk Operating System (DOS)

©Brooks/Cole, Parallel System The need for more speed and effecincy has led to the design of parallel systems; multiple CPU in the same machine. Each CPU can be used to serve one program which means that many task can be accomplished in parallel. These OS are more complex than the ones with single CPU.

©Brooks/Cole, Distributed System Networking has created a new operating systems. In these system, jobs that was previously done in one computer can be shared between computers that are physically separated. In these OS, resources can be distributed. Dr. Barnawi

©Brooks/Cole, 2003 COMPONENTSCOMPONENTS 7.3

Figure 7-2 Components of an operating system

©Brooks/Cole, 2003 Memory Manager Memory allocation must be managed to prevent the “running out of memory ” syndrome. Operating systems can be divided into two broad categories of memory management: 1.Monoprogramming 2.Multiprogramming.

©Brooks/Cole, 2003 Figure 7-3 Monoprogramming Not used anymore. Most of the memory is dedicated to one single program with only a small part used to hold the operating system. When a program finishes running, it is replaced by another program Dr. Barnawi

©Brooks/Cole, 2003 Problems with monoprogramming The program cant run if the size of the program is greater than the size of the memory. When the program runs, no other program can be executed.

©Brooks/Cole, 2003 Figure 7-4 Multiprogramming More than one program are in the memory and can be executed concurrently. CPU switches between the programs

©Brooks/Cole, 2003 Figure 7-5 Categories of multiprogramming Programs stay in memory during execution Programs can swap between memory and disk during execution Dr. Barnawi

©Brooks/Cole, 2003 Figure 7-6 Partitioning Memory is divided into sections. Each holds a program CPU switches between programs. It starts with one program and execute some instructions until either encounters I/O operation or time for program run out. The CPU will save the address of last instruction and move to the next program. CPU will get back to the first program after all programs are served

©Brooks/Cole, 2003 Partitioning (Issues) Memory manager determines the partition size  If partition sizes are small, programs cannot be loaded in the memory.  If partition sizes are large, there might be some holes (unused locations) in the memory. When there are many holes, memory manager removes the holes and create new partitions, this would create extra overhead on the system. Dr. Barnawi

©Brooks/Cole, 2003 Figure 7-7 Paging Memory is divided into equal sized sections (frames) Program is divided into pages The size of the page and frame are the same and equal to the size of the block used to retrieve data from Disk. The page is loaded to the memory. The program doesn’t have to be contiguous

©Brooks/Cole, 2003 Paging (issues) Advantage of paging that it doesn’t need OS to partition the memory as the size of programs changes. Paging improves efficiency but the whole program needs to be in memory before being executed

©Brooks/Cole, 2003 Demand Paging Paging require the entire program to be in memory. However demand paging, pages can be loaded one by one, executed and then replaced by new pages. Memory can hold one page from multiple programs at the same time.

©Brooks/Cole, 2003 Demand Segmentation A program is usually made of a main program and subprograms. In Demand Segmentation, the program is divided into segments (modules) that match the programmer’s view. Modules are loaded into the memory, executed and replaced by another module from the same or different program.

©Brooks/Cole, 2003 Demand Paging and segmentation A segment (module) may be too large to fit any space in memory. In this case, module is divided into pages and each page is loaded into memory and executed one by one.

©Brooks/Cole, 2003 Figure 7-8 Virtual memory (swapping)- Example 6 MB 24 MB 6 programs each 4 MB At one time, 1 MB of each program is in the memory and 3 MB are in the Disk. Program #1 #2 #3 #4 #5 #6 Frame (1 MB) Page (1 MB) Dr. Barnawi

©Brooks/Cole, 2003 Process Manager Operating system uses three terms; Program; A non active set of instruction that stored in the disk. Job; is a program that is picked by the CPU for execution. Process; is a program in execution.

©Brooks/Cole, 2003 Figure 7-9 State diagram with the boundaries between a program, a job, and a process

©Brooks/Cole, 2003 Figure 7-10 Job scheduler Job scheduler is responsible for creating a process from job and terminating a process.

©Brooks/Cole, 2003 Figure 7-11 Process scheduler Process scheduler moves a process from one state to another. Dr. Barnawi

©Brooks/Cole, 2003 Queuing There are many jobs and processes and process competing with each other for computer resources. To handle multiple processes and jobs, the process manager uses queues. Job control block stores information about jobs. Process control block stores information about processes.

©Brooks/Cole, 2003 Figure 7-12 Queues for process management Process manager has different priority polices for selecting the next job or process; FIFO, short first…

©Brooks/Cole, 2003 Process Synchronization The whole idea of process management is to synchronize different processes with different resources. Whenever resources are shared, two different situations are created: –Deadlock –Starvation Dr. Barnawi

©Brooks/Cole, 2003 Figure 7-13 Deadlock

©Brooks/Cole, 2003 Figure 7-14 Deadlock Deadlock occurs if all of the following conditions are met: 1.Mutual Exclusion; only one process can hold resources at a time. 2.Resource holding; process holds the resource until other resource is released. 3.No pre-emption; the O. S. cant temporarily reallocate resources. 4.Circular waiting; all processes and resources form a loop.

©Brooks/Cole, 2003 Figure 7-15.a Starvation Starvation happens when OS puts too many restriction on resources

©Brooks/Cole, 2003 Figure 7-15.b Starvation Dr. Barnawi

©Brooks/Cole, 2003 Figure 7-15.c Starvation Dr. Barnawi

©Brooks/Cole, 2003 Figure 7-16 Dining philosophers-Dijkstra

©Brooks/Cole, 2003 Device Manager accessing I/O devices The device manager; Monitors every input/output device constantly to assure it is functioning properly. Maintains a queue of each I/O devices or one or more queues for similar I/O devices. Controls the different polices for accessing I/O devices.

©Brooks/Cole, 2003 File Manager accessing the files The file manager Controls access file; access is permitted only to those allowed, and the type of access can vary. Supervises the creation, deletion… of files Controls, naming. Manages where, how… files are stored. Responsible for archiving and backups.

©Brooks/Cole, 2003 User Interface User interface accepts requests from users and interpret them to the rest of the O.S. User interface in Windows series is a Graphical User Interface (GUI) Dr. Barnawi

©Brooks/Cole, 2003 POPULAROPERATINGSYSTEMSPOPULAROPERATINGSYSTEMS 7.4