For Mitsubishi Electric's MELCOM-3100 series announced in 1966, Model 10T operating system, Model 10PT operating system and Model 30T operating system were provided. These operating systems used magnetic tapes as external storage and were developed by systematically organizing and enhancing the system programs built up with MELCOM-1530.
1. Model 10T operating system
The Model 10T operating system was based on card input, and the corresponding standard hardware consisted of a main memory with the capacity of 24K characters, a typewriter, a card reader, a card punch, a line printer and 4 to 8 magnetic tape devices. The system was operable without a card punch.
The operating system comprised a control program and processing programs. The control program was the core of the operating system, consisting of a system supervisor, a job processor and a debugging routine. These elements were responsible for tasks such as reading and writing programs and data between memory and devices, controlling program executions, processing interrupts and abnormal events, processing jobs and communicating with operators. The processing programs included compliers of languages such as COBOL and FORTRAN, a MACRO-CODER, an assembler, utility programs including SORT and MERGE, and application programs such as LP and PERT. User-created programs were also included amongst the processing programs.
As indicated in the figure, a source program was read from a card reader or a magnetic tape, converted into a Primary Object Program by a compiler or an assembler, written to a card or magnetic tape, and then read by a loader called PL (Primary Loader) and executed. It was also possible to register in advance repeatedly used programs in a program library (in a magnetic tape) by converting them into Secondary Object Programs using SMP (System Maintenance Program), and later read the desired program using a loader called SL (Secondary Loader) and execute it. In converting a card to a magnetic tape, JPP (Job Preparation Program) was used. To achieve a compact configuration, a function for editing object codes was omitted and object codes were created in absolute format.
Process of programs in MELCOM-3100-10T
To enable automatic and continuous processing of multiple jobs, Job Control Statements were used. A Job Control Statement began with “///,” followed by operation code and parameters. The figure below shows an example of a sequence of jobs:
Example of input to the system for card base sequential job processing.
2. Model 10PT operating system
Model 10PT operating system used a paper tape instead of the card employed in the Model 10T operating system. Therefore, support was provided for the maintenance of a source program on a paper tape and for the different formats of paper tape devices.
The operator could update a source program on a paper tape by connecting a tape on which only the updated part had been punched to the end of the original source program tape, and then compiling or assembling it. To prevent the increasing differences between a source program and its list as a result of repetitive updating, a function for punching the updated source program was also provided.
A software called Input Controller converted the code of source program on a paper tape using a conversion table during reading. To support various code patterns of paper tape devices, a code conversion table maintenance program was provided.
3. Model 30T operating system
The Model 30T operating system was capable of operating larger systems more efficiently. Objects were created in relocatable format; it was possible to divide and code a large program into segments, and to create an executable program by connecting the object codes. It was also possible to create a program in segment structure or overlay structure in order to reduce the limit on the main mamoery capacity. To accelerate the loading of a program on a magnetic tape, a program directory was placed before the program group.
Flow of program processing with MELCOM-3100 30T
In addition, a SPOOL function was used to realize simultaneous operation of the calculation processing in the central processor and the input/ooutput operations from/to a card reader, printer or card punch, thereby increasing the throughput of the system. A Job Control Statement was used to specify whether or not the SPOOL function to be used.