Text B. Kinds of programs

There are two main kinds of programs which are subdivided as well. They are control programs and systems service programs.

Control Programs. There are some control programs to handle interruptions (прерывание), I/O operations, transition between different jobs (задание) and different phases of the same job, initial program loading (IPL), and symbolic assigment of I/O devices.

Actually, the control program consists of three components:

1. IPL loader. When system operation is initiated, the hardware IPL reads in this program which then clears unused core storage to zeros, generally performs some housekeeping operations, and then reads in the Supervisor.

2. The Supervisor. It is resident in the low order part core storage whenever any job is being run. It can handle execution of any I/O operations and can provide standard processing for all interrupts. It may also queue I/O operations so that the operation will start as soon as the required channel and device are free.

3. Job Control. When the end of a job is sensed, the user normally turns control over to the Supervisor which then reads in the Job Control program. This program senses and processes all cards; after, the new job is loaded, it turns control over to the new job. This/system of operation eliminates the necessity of operation intervention between jobs, something which is of particular importance on large computers where the average job time may be less than one minute.

The control program is a large program occupying thousands of bytes. It is usually stored on a magnetic tape or a magnetic disk.

The particular unit on which the program resides is called the System Resident unit.

System Service Programs. They are used to maintain the library, to place new programs into the library, to delete, replace, or change existing programs, to read programs from the library into memory, to link segments of programs written at different times into one program, etc. They are called Librarian8 and Linkage Editor.

There are three libraries maintained by the Librarian program: 1) Core Image library, 2) Relocatable library, 3) Source Statement library.

The core image programs includes the processors and control programs and as many of the application programs as the user desires. The relocatable library contains modules which are stored in such a way that each module can be arbitrarily relocated and still be executed correctly. A module may be a complete program or it may be a relatively independent part of a larger program. The source statement library contains macro definitions a sort of collection of standard type statement which can be incorporated into a program to provide some special functions.

Notes

1. control programs - управляющие программы

2. unused core storage - неиспользованная часть ОЗУ

3. housekeeping operations - вспомогательные операции

4. Job Control - управление потоком заданий

5. the average job time - среднее время счета задания

6. System Resident unit - системное резидентное устройство

7. System Service program - системная сервисная программа

8. Librarian - программа «Библиотекарь»

9. Linkage Editor - программа «Редактор связей»

10. Core Image library - загрузочная библиотека

11. Relocatable library - перемещаемая библиотека