1.2 Mainframe Systems

Reduce setup time by batching similar jobs .Automatic job sequencing – automatically transfers control from one job to another. First rudimentary operating system. Resident monitor. initial control in monitor .control transfers to job .when job completes control transfers pack to monitor

Memory Layout for a Simple Batch System

Multi-programmed Batch Systems

Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them.

OS Features Needed for Multiprogramming I/ O routine supplied by the system.

Memory management – the system must allocate the memory to several jobs.

CPU scheduling – the system must choose among several jobs ready to run.

Allocation of devices.

Time- Sharing Systems– Interactive Computing

The CPU is multiplexed among several jobs that are kept in memory and on disk

(the CPU is allocated to a job only if the job is in memory).

A job swapped in and out of memory to the disk.

On- line communication between the user and the system is provided;

when the operating system finishes the execution of one command, it seeks the next “control statement” from the user’s keyboard.

On- line system must be available for users to access data and code.