An Operating Systems Vade Mecum

Historical development 5executing jobtypewritercard readerprinteruserFigure 1.1 Open shopblock of time.3.2 Operator-driven shopThe economics of computers made such idle time very expensive. In an effort to avoidsuch idleness, installation managers instituted several modifications to the open shopmechanism just outlined. An operator was hired to perform the repetitive tasks of loadingjobs, starting the computer, and collecting the output. This situation is shown in Figure1.2. The operator was often much faster than ordinary users at chores such as mountingcards and magnetic tapes, so the setup time between job steps was reduced. If theprogram failed, the operator could have the computer produce a dump. It was no longerfeasible for users to inspect main store or patch programs directly. Instead, users wouldsubmit their runs, and the operator would run them as soon as possible. Each user wascharged only for the amount of time the job required.The operator often reduced setup time by batching similar job steps. For example,the operator could run the first pass of the Fortran compiler for several jobs, save all theintermediate output, then load the second pass and run it on all the intermediate outputthat had been collected. In addition, the operator could run jobs out of order, perhapscharging more for giving some jobs priority. Jobs that were known to require a long timecould be delayed until night. The operator could always stop a job that was taking toolong.