Operating System Quick Guide Learning operating system concepts in simple and easy steps A beginners tutorial containing complete knowledge about an operating. Operating Systems. An operating system is a program that acts as an intermediary between a user of the PC and the hardware. A computer system can be abstracted into various components. Users people, or other machines and systems interact with system and application programs defines the way in which system resources are used to solve the computing problems of the users, which interact with the OS controls and co ordinates the use of hardware among the various application programs for the user, which interacts with the hardware the most basic computing resources CPU, memory, IO, etc. When developing an OS, all levels must be considered, not just the OS level. For users, they interact with the hardware monitor, keyboard, mouse, etc to control the system and application programs. The program needs an efficient interface to interact with the OS to utilise the resources it needs to accomplish the tasks the user wants to do and to also communicate with the user. C program for implementation of FCFS scheduling includeltiostream using namespace std Function to find the waiting time for all processes void. These systems had minimal operating systems and were typically mainframe computers used to support commercial and scientific applications. Jobs and programs were. University of Pune Pattern 2013 w. e. f. 2014 15 B. C. A. Semester III Subject Name RDBMS Relational Database Management System Course Code 301. In computing, scheduling is the method by which work specified by some means is assigned to resources that complete the work. The work may be virtual computation. Scheduling of processeswork is done to finish the work on time. Below are different time with respect to a process. A typical process involves both IO time and CPU. Enter your email address to subscribe EDUGRABS and receive notifications of new posts. OUTPUT enter no of processes 5 enter process1 name aaa enter process time 4 enter process2 name bbb enter process time 3 enter process3 name ccc enter. The OS interface describes the calls that an application program can make into the OS. The OS is designed for ease of use, which is in terms of not having to deal with low level hardware issues. This is more important than CPU usage a user doesnt care if the CPU is idle 9. The goal of OS design is to provide a useful, simple and efficient system ease of useminimise resource usagemaximise resource utilisation. However, abstraction away from the physical machine to provide ease of use can lead to inefficiencies. Theres a trade off required between the extra functionality of the virtual machine and the overheads required to implement this. Generation 1. 94. These are systems which didnt have operating systems. Users had complete access to the machine and the interface was basically raw hardware. Programming was accomplished by wiring up plugboards to control basic behaviour of the computer the problems to be solved were normally numerical calculations. Operating systems and programming languages were virtually unheard of. Generation 1. 95. These systems had minimal operating systems and were typically mainframe computers used to support commercial and scientific applications. Jobs and programs were written using punch cards and the computers were normally application specific. The minimal OS was required to interact with IO devices and a subroutine library existed to manage IO interaction. The library is loaded into the top of memory and stays there. Application programs existed compilercard reader, but were limited. Optimisations could be made in reducing the setup time by batching similar jobs. A small computer reads a number of jobs onto magnetic tape and the magtape is run on the mainframe. A number of jobs is then done in succession without wasting CPU time. These systems had a small permenantly resident OS which had initial control and controlled automatic job sequencing. These systems had a new memory layout and the processor had two modes Normal, where some instructions e. HALT are forbidden, which was used by the batch programs, and Privileged, where all instructions are available, this was the level the OS ran in. Some CPUs also implemented protection in Normal mode to prevent the user program overriding the first section of memory in which the OS existed. Normal mode also has an instruction to call the OS hand back control. Batch systems were good for CPU bound scientific computing with minimal IO, but bad for data processing with high IO as the CPU is often idle. The speeds of the mechanical IO devices is considerably slower than that of the electronic computer and jobs often have to pause when performing IO. In some cases, the CPU was often idle for 8. However, with a permenantly resident OS in the memory, the OS now becomes an overhead, with less physical memory available for the application running at the time. Programming discipline in the application is still required as the OS can not protect against the application crashing the machine via bad IO, infinite loops, etc. Generation 1. 96. The introduction of ICs led to minicomputers, which tried to merge the scientific computers with IO computers and this introduced multiprogramming. Disk drives allowed jobs and programs to be stored on disk, allowing the computer to have access to many jobs. The CPU can now load many jobs into memory by giving each one a memory partition and then execute them by multiplexing between them. In these OSs, the OS picks a job and then passes control to it. Eventually, the job either finishes or waits for some task e. IO to complete. In a non multiprogrammed system, the CPU would now be idle. In a multiprogrammed system, the OS switches the CPU to another job. Eventually, the operation the original job was waiting for completes, enabling that job to be eligable to be waiting for CPU time. As long as there is at least one job waiting to execute, the CPU is not idle. When a job completes, the OS can load another job into that memory slot. This technique is called spooling Simultaneous Peripheral Operation On Line, and is still used today for operations such as print queues. Multiprogramming OSs are quite complex they now handle quite complex IO devices disks, etc and swapping between applications when suspended on IO. Multiprogramming works best when there are a small number of large jobs this reduces the overhead of the OS due to managing memory between less jobs. This method also encourages a fairer overall use of the computer. Multiprogramming systems led on to time sharinginteractive systems. The CPU here is multi plexed between several jobs that are kept in memory and on disk. The CPU is allocated to a job only if the job is in memory. When a job waits on IO, the OS switches the CPU to another job. Jobs can also be switched in between memory and the disk. On line communication between the user and the system is provided when the OS finishes the execution of one command, it seeks the next control statement from the users keyboard. In time share systems, the user has the illusion of using the computer continuously and the user can now interact directly with the computer whilst it is running. This encourages smaller jobs and more efficient use of the computer. Additionally, many users can share the computer simultaneously, submitting jobscommands directly via keyboardsterminals, etc. The first time sharing system was CTSS, developed by MIT. This formed the basis for MULTICS, the first commercial OS that had limited success. UNIX was then developed by Bell Labs in the high level language C, based on B. Generation 1. 98. The fourth generation of operating systems broguth about the first mass user operating systems, as LSI and VLSI enabled low cost computing, with mini and desktop computers becoming common. The age of mass computing is based around desktop computers. The desktop PC is dedicated to a single user and the distinction between desktop and minicomputers become increasingly blurred. Many minicomputers are now merely highend desktop PCs, with advanced IO capabilities and multiprocessors. The multiprogrammed OS UNIX, VMS, etc was developed further for mass user computers, adding functionality like massive file storage, fast networking, complex application programs and the potential for multiprocessor. Modern desktop systems have dedicated single user OSs e. MCS 0. 41 IGNOU STUDY MATERIAL by IGNOU MCAMCS 0. IGNOU STUDY MATERIAL   Published on May 9, 2. MCS 0. 41 IGNOU STUDY MATERIAL. Issuu is a digital publishing platform that makes it simple to publish magazines, catalogs, newspapers, books, and more online. Easily share your publications and get.