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Industrial Computer Systems 6032B Mount Druitt College of TAFE Lesson 3 © Mike Stacey 2008 1 Today’s Topics Batch processing Timesharing Batch files © Mike Stacey 2008 2 Batch Processing and Timesharing Industrial Computer Systems Mt Druitt College of TAFE Semester 1, 2008 © Mike Stacey 2008 3 Early Operating Systems Program execution required preparation of equipment mounting tapes placing punched cards in the card reader setting switches and so on If multiple users wanted to share a machine, sign on sheets were provided so that users could reserve a machine for a period of time (session) © Mike Stacey 2008 4 Batch Processing Development of computers was involved with streamlining the transition between jobs and simplifying program set-up Computer operator hired to perform the operation of the machine. Users were not permitted into the computer room. Users submitted their program along with written instructions to the computer operator and returned later for the results Operator loaded the programs into the machine’s mass storage where the operating system could access them for execution This was the beginning of BATCH PROCESSING the execution of jobs by collecting them in a single batch, then executing them without further intervention from the user the jobs residing in mass storage awaited execution in a job queue © Mike Stacey 2008 5 Disadvantage of Batch processing No user interaction with program while being run OK for jobs such as payroll processing Not OK for jobs such as airline reservations – cancellations and reservations must be entered as they occur New operating systems were developed to accommodate these needs Execution of programs carried on a dialogue with the user (interactive processing) Still a problem that only one program can execute at any one time © Mike Stacey 2008 6 Multitasking - Timesharing So the next development was to allow multiple programs to simultaneously run on the machine The operating system rotates jobs (programs) in and out of execution Each process is allocated a time slice and can only execute during that interval of time Called Timesharing If this process is performed with great speed, the illusion of several jobs running at the same time is created © Mike Stacey 2008 7 Example of Timesharing These days, everyone sees examples of timesharing when they are running more than one program at once on a PC MS Word, MS Excel, Internet Explorer, Windows Explorer are all separate processes (programs, jobs) and they appear to be running simultaneously In reality they are running as follows: © Mike Stacey 2008 8 Scheduling algorithms Various different algorithms control which process is running at a particular time One of the more common scheduling algorithms is called Round Robin scheduling © Mike Stacey 2008 9 Round Robin Scheduling P2 P3 P1 2 time units CPU executing 2 time units P4 2 time units 2 time units 2 time units P8 2 time units 2 time units P7 Some examples of P1, P2, P3 etc would be? P5 2 time units P6 Run process for one time slice then move it to back of job queue, load next process into memory, execute it... © Mike Stacey 2008 10