PDP-7 Program Library

This document describes the "FB Dectrieve" program for the PDP-7 computer, designed to facilitate saving and retrieving memory areas on DECtape. Its primary purpose is to allow programmers to store specific sections of memory onto DECtape and then quickly retrieve that information using the toggle switches on the PDP-7.

To store data, the user specifies the DECtape unit, the starting block, and the core memory's starting and ending addresses via the Accumulator (ACS) and program execution steps. The program stores the data along with four words of control information for later retrieval, filling any incomplete last blocks with zeros. Upon successful completion, it types a message indicating the starting and ending tape blocks and a total checksum. All written data is verified by re-reading and checksum accumulation.

For retrieval, the user similarly specifies the DECtape unit and the starting block where the information was stored. The program then uses the stored control information to load the data into the correct memory registers. A completion message, similar to the storage message but with a "Read" indication, is typed. Error messages are provided if the requested block is not the start of a stored area.

The document also provides detailed instructions for using DECTRIEVE as a subroutine within other programs, including modifications to handle data storage/retrieval formats, error conditions, and suppressing standard completion messages. The program occupies about 1260 octal words of memory and is available in versions for different memory locations (6000 or 16000) and DECtape controls, compatible with 4K or 8K machines. It notes that Registers 0 and 10 are overwritten, but Register 1 is preserved.