Spooling and offline operations for overlapped I/O have their limitations. The main characteristic of job scheduling is the ability to multiprogram. Jobs scheduling become possible when several jobs are on a direct access device such as disk. Jobs execute on the bases of first come, first serve so they must run in sequential fashion. When jobs come in direct manner on magnetic tape or cards jobs cannot run in a different order. Disk which contains a pool of jobs allows operating system to select job to run next for sack of CPU’s proper utilization. Spooling deals with several jobs that have already been read waiting on disk ready to run. spooling process were used to pint the output from the line printer in which card reader was used to take the input and disk is use copy the command into system buffer and written to the disk CPU read command from dick execute it and send back to disk then ultimately output is printed at line printer. In this case of execution environment, the CPU is often idle. The delay in turnaround time may result from the amount of computing needed or from delays before the operating system starts to process a job. This system usually reads a stream of separate jobs and each has its own control cads with predefined job’s task. Computer run the batches one by one when it became available. The programmers used the operators in programs to make the batches with similar requirements. To enhance the processing speed jobs with similar needs were bathed together and were run as a group through the processor. Its main task was to transfer the control from one job to the next in automatic manners. The output of the program was consisted of results as well as registers and dumps of memory in case of program errors. Output appeared after some time it may took minutes, hours or days. Then this job was submitted to the computer operator which were usually in the form of punch card. In simple batch operating system user did not directly interact with computer system for job execution rather, the user required to prepare a job which entailed of the program the control information and data about the nature of job the control cards. Users did not have direct interaction with system and execution of jobs were done in batched system this kinds of systems called as batched operating systems in which user have to prepare a jo separately to get them executed. Generally, devices used for I/O were tape driver or card readers for input and tape derives, punch cards and line printers for output. Batch Operating System – Computer were extremely large machines in early times which run from console.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |