User`s guide

How Data Is Stored in Files
— LDA Files
Load-image (LDA) files are ones that you can produce, load, and execute in
stand-alone environments without relocating them.
— SYS Files
Operating system files and handler files (SYS) are those that run the
operating system and let you process input and output on devices.
For more information about these file types, see the RT–11 Volume and File Formats
Manual.
Using Files, Volumes, and Devices 3–11