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LOADGO Header Records
17 January 1975
Technical paper 2
ACL intends to use the LOADGO system on the FR80 microfilm recorder. This system is designed to increase throughput by eliminating the operator intervention required to load programs and to enter monitor commands. LOAD GO allows jobs which are intended to run under different monitors to be submitted on a single tape, and provides for the automatic loading of the correct monitor for each job. In order to accomplish this, each job on the tape is prefaced by two header records. The first of these contains the name of the monitor program that is to run the job, while the second contains a set of monitor commands which are to be obeyed by the chosen monitor program before it begins the processing of the graphical data which follows. It is the responsibility of packages which generate FR80 output to construct these header records.
The appearance of the final graphical output depends not only on the commands which appear in the second header record, but also upon the precise variant of the FR80 Displayer which is named in the first header record. The FR80 Displayer will exist initially in four variants; more may be added later. One pair of variants is for use with the microfiche camera only, while the other pair is for use with any of the roll-film cameras. The two variants within each of these pairs consist of one version which incorporates a simple character font, and another which includes a rather more sophisticated one. The simple font takes up less space within the FR80 processor and is more quickly drawn than the other. It should be quite suitable for general purpose output while the sophisticated font will be more suitable for work. intended for publication.
2. TAPE FORMAT
The jobs recorded on a tape for use with the LOADGO system must be separated from one another by single filemarks. A.double filemark is used to terminate the tape. The first two records of each job are the LOADGO header records while the remaining records contain the graphical data. Single filemarks appearing between data records do not upset the system.
ACL conventions restrict all programs which generate FR80 output to the following tape layout:
- LOADGO first header record
- LOADGO second header record
- Graphical data records
- Double filemark.
The filemark between the header and the data records permits the start of the data to be found should it be necessary to load monitors manually in the event of a breakdown in LOADGO. Tape images sent to the 1906A SPOOL should also conform exactly to the above layout.
The two header records consist logically of 18-bit words which are represented on tape by three consecutive characters (7-track) or bytes (9-track). Each header record is restricted to a maximum length of 256 (decimal) words. Careful note should be made of the fact that the two header records employ differing character codes and pack characters into words differently.
The paper continued with precise details of each of the records so that the various graphics systems could generate the correct records needed to spool jobs to the FR80.