DECsystem-10 DECtape Bootstrap Jun73

This document describes DTBOOT, a bootstrap program for the DECsystem-10, released on June 14, 1973 (Edition 4). DTBOOT's primary purpose is to transfer programs between the DECsystem-10's core memory and standard DECtape files, as well as providing other utility functions for DECtapes. It is designed to load and run executive mode programs (like monitors and diagnostics) and requires a DECsystem-10 central processor, core memory, a console typewriter, DECtape control, and at least one DECtape transport.

Key Functions: DTBOOT provides a range of functions controlled by a simple command string with useful defaults. These include:

1. Program Loading & Execution: Clearing core, loading a program, and optionally starting it; or loading a program without clearing other core areas.
2. Core Dumping: Dumping the current core memory onto a DECtape file.
3. File Management: Typing out a short directory, deleting files, and initializing an empty tape directory (with an optional new identifier).
4. Program Control: Declaring and jumping to a specific starting address for a program.

Command Structure: Commands are entered through the console typewriter. They typically include a DECtape unit specifier (e.g., DTA3:), a filename (defaulting to .SAV extension, CRASH for writing, or SYSTEM for reading if multiple files exist), and an optional switch (e.g., /L for load) to specify the action. If no switch is given, DTBOOT defaults to loading and starting the program.

Tape Format and Compatibility: DECtapes written and read by DTBOOT are fully compatible with the DECsystem-10 monitor (TOPS10). DTBOOT is intended to supersede an earlier program called TENDMP. Its advantages over TENDMP include:

• Ability to read long .SAV files that utilize both forward and backward tape allocation.
• More efficient writing of files, reducing "tape rocking" when read by TOPS10.
• More complete DECtape control and standard command strings.
• The ability to set tape-identifier words. The only known incompatibility with TOPS10 is that DTBOOT does not provide dates on output files.

Assembly and Loading: DTBOOT is assembled by MACRO-10 into RIM10B format and loaded via READIN at the PDP-10 console. It resides at the top of user core and must be assembled for the specific memory size of the system (e.g., 64K), starting at an address 1000 octal less than the core size. DTBOOT itself can be stored in the bootstrap blocks (0, 1, 2) on a DECtape.

Errors are indicated by the console bell ringing, and can include issues like an inaccessible tape unit, parity errors, or files not found in the directory.