DECtape Copy Program

This document describes the DECtape Copy Program, designed for PDP-7 systems (with 4K or 8K memory, but not PDP-4) to copy all or part of one DECtape onto another. The program requires two DECtape drives connected to a PDP-7 DECtape control. It operates by reading a series of blocks from the source tape, writing them to the destination tape, and then rereading the newly written blocks for checksum verification and comparison with the original data. Errors during this process will cause an identifiable halt. Users specify the first and last block numbers to be copied (from 1 to 1100) using the console ACCUMULATOR switches. The program dynamically allocates memory for reading and comparison areas based on the system's memory size (e.g., 3000g locations for each area on a 4K machine, 7000g on an 8K machine). It supports standard DEC formats (1100g blocks of 400g words) and is suitable for tape duplication and backup, with a full reel copy and verification taking approximately 3 minutes on an 8K system or 4 minutes 20 seconds on a 4K system. Block 0 cannot be copied.