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2 - 2 Management Functions of OS

Among the various functions that are provided by an OS, job management, task management, and memory management are sometimes called the three main functions of an OS. On the basis of these three main functions, this section explains the various management functions of an OS.

2-2-1 Job Management

Job management is a function that manages the execution of jobs, which are the unit of activity from the perspective of a user. Generally, a job is defined as a set of job steps. A job step is a single unit of a divided work. Job management allocates resources to each job (i.e., job step), and it performs things such as consecutive execution of jobs. The general flow (i.e., procedure) for executing jobs with job management is shown below.

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Job management uses functions (1) to (3) below in order to implement this procedure for job execution.

(1) Spooling

Spooling is a method that enables a peripheral device (i.e., an input/output device) to operate in parallel and independently of a CPU. Specifically, it is a method that performs data transmission between a main memory unit and a low speed input/output device via a high-speed auxiliary storage device (spool). This releases the CPU from transmission waiting time and improves the throughput of the system overall. The term buffering is sometimes used to generally refer to a method such as spooling that uses an area (i.e., buffer) of memory to store data and transmits the data between devices that have different access speeds. · 2 questions

(2) Job scheduler

A job scheduler is a program that automatically executes jobs. It manages the control flow for jobs and also performs job scheduling, which selects a job to be executed from waiting jobs.

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(3) Master scheduler

A master scheduler is a program that mainly manages the interface between the user and the computer. It transmits directions (e.g., JCL) relating to job execution and various types of messages between the user and the computer.