TC59 Random Exerciser

The TC59 Random Exerciser is a diagnostic program designed to simulate tape system usage on a PDP-9 computer system. Created on May 17, 1968, by Keith R. Nelson from the Diagnostic Group, its primary function is to test configurations of 1 to 8 TU20 (or similar) seven and/or nine-track magnetic tape drives concurrently.

Before running the exerciser, prerequisite programs such as the TC59 Control Test and Drive Function Timer must be executed. The loading procedure involves two ABS Binary Tapes (MAINDEC-9A-D4FA-B for the Executive Routine and MAINDEC 9A-D4GA-B for the exerciser itself) loaded via a paper tape reader. The program starts at address 00200, after which system parameters, including drive selection (1-8 drives, 7 or 9 track), are entered via the TTY (keyboard).

The program simulates real-world tape usage by randomly selecting the drive, data pattern, parity, density, record length, file length, and sequence of operations. It uses a "FILE STRUCTURED" tape format, where each file consists of 6 to 63 identical records and an End of File (EOF) mark. Record lengths can vary from 9 to 1023 PDP-9 words, with patterns generated from seven random words. Parity and density are usually random but can be fixed using operation switches.

The TC59 Random Exerciser includes comprehensive error detection and reporting. All detected errors result in a typeout, detailing the drive, command, status, file, and record position. Errors are categorized as write status errors, read status errors, catastrophic drive errors (e.g., bad tape, unexpected EOF), system/control failures (e.g., unexpected interrupts, hung controls), and data errors. The program attempts various recovery procedures, such as backspacing and rewriting for write errors, or backspacing and rereading for read errors. However, persistent failures or catastrophic errors lead to the affected drive being rewound to its load point and restarted. Data errors are reported by comparing expected data words with actual words read.