Tiêu đề Operating System Complete BCA Notes Pdf.pdf ✅

www.ckundan.com.np 3 Because the user is present and interacting with the computer, the computer system must respond quickly to user requests, otherwise user productivity could suffer. Timesharing systems were developed to multi-program large number of simultaneous interactive users. The 1970’s-Fourth Generation: With the development of LSI (Large Scale Integration) circuits, chips, operating system entered in the system entered in the personal computer and the workstation age. Microprocessor technology evolved to the point that it become possible to build desktop computers as powerful as the mainframes of the 1970s. Two operating systems have dominated the personal computer scene: MS-DOS, written by Microsoft, Inc. for the IBM PC and other machines using the Intel 8088 CPU and its successors, and UNIX, which is dominant on the large personal computers using the Motorola 6899 CPU family. Objectives of Operating System: 1.Operating System as an Extended Machine or Virtual: The operating system masks or hides the details of the Hardware form the programmers and general users and provides a convenient interface for using the system. The program that hides the truth about the hardware from the user and presents a nice simple view of named files that can be read and written is of course the operating system. Figure: Computer System Consists Of Hardware, System Program and Application Program In this view the function of OS is to present the user with the equivalent of an extended machine or virtual machine that is easier to program than underlying hardware.
www.ckundan.com.np 4 Just as the operating system shields the user from the disk hardware and presents a simple file-oriented interface, it also conceals a lot of unpleasant business concerning interrupts, timers, memory management and other low level features. The placement of OS is as shown in figure below. A major function of OS is to hide all the complexity presented by the underlying hardware and gives the programmer a more convenient set of instructions to work with. 2.Operating System as a Resource Manager: A computer system has many resources. Modern computers consist of processors, memories, timers, disks, mice, network interfaces, printers, and a wide variety of other devices. Figure: The Operating system as Resource manger In the alternative view, the job of the operating system is to provide for an orderly and controlled allocation of the processors, memories, and I/O devices among the various programs competing for them. Imagine what would happen if three programs running on some computer all tried to print their output simultaneously on the same printer. The first few lines of printout might be from program 1, the next few from program 2, then some from program 3, and so forth. The result would be chaos. The operating system can bring order to the potential chaos by buffering all the output destined for the printer on the disk. When one program is finished, the operating system can then copy its output from the disk file where it has been stored to the printer, while at the same time the other program can continue generating more output, oblivious to the fact that the output is not really going to the printer (yet).