DIAL-MS Loader Program Description

This document describes the DIAL-MS Loader Program, a critical component of the LAP6-DIAL system designed for the PDP-12 computer. Its primary function is to transfer user binary programs from tape or disk into specific core memory locations.

The loader operates in two main sections: first, it determines if a program is to be loaded by name or from the Binary Working Area. Second, it utilizes a subroutine to search for the program's name within an index and then proceeds with the actual data loading. If the program file is not found, control is returned to the caller.

Key operational details include:

• The loader occupies blocks 54 and 55 of the DIAL systems unit and is loaded into locations 4000-4777 of field 1. An extension, the "mini-loader," resides in 7600-7627 of field 1.
• It begins execution in LINCmode at location 4020 of field 1, checking for a program name.
• If a name is provided, it calls a load subroutine; otherwise, it loads a default block from the Binary Working Area and constructs a header block to facilitate loading the entire 8K binary area.
• The load subroutine, which can be called from any field, reads an index, searches for the desired program name, and if found, loads up to 17 blocks into core.
• It manages complex memory transfers, moving data between different memory fields to avoid data break location issues and utilizing bit maps to determine which blocks of the program are loaded into various memory regions.
• The mini-loader uses a mini-bit map to precisely determine and load subsequent blocks before transferring control back in LINC-mode.

The document also acknowledges that the LAP6-DIAL system's editor, filing, and assembly portions are derived from Mary Allen Wilkes's LAP6 LINC program and PDP-8 programs, including PAL-D. It indicates the presence of a flow diagram and program listing for further detail.