Upgrading M3SE with LS-DOS

Note: The LS-DOS operating system is for Model 4/4D/4P systems only. It does not work with the Model III, so there is no reason to install it on a M3SE which will only be used with a Model III.

M3SE units sold after March 20, 2016 come with LS-DOS 6.3.1 pre-installed, so owners of these systems should not follow the instructions on this page. Instead, read the section on using LS-DOS with M3SE for instructions.

M3SE units sold before that date are easily upgraded to include LS-DOS. First, read about using multiple hard disk images to understand the basic concept since you will be installing LS-DOS onto an alternate CF image.

The recommended configuration is to leave LDOS 5.3.1 installed on CF image 0, and install LS-DOS onto (at least) CF image 1. There is no restriction on which image(s) you can use, but the M3SE PCB has a dual DIP switch on-board; with switch 1 in the "off" position, M3SE will boot from CF image 0 after powerup or reset. With switch 1 in the "on" position, M3SE will instead boot from CF image 1. Therefore the switch can be used to select your desired default operating system if you install LS-DOS onto CF image 1.

The next step is to make sure you have recent versions of the LDOS IDEBACK and IDEBOOT utilities. Running each of these programs without arguments should list a version number of 2.0 or greater. If yours are older, you can download the latest versions from the archives here and install them on CF drive :0. Remember, you might have to log in using the password UTILITY or the system password RS0LT0FF to overwrite these files.

Next, download the image file M3SELSDS.IMG and use FTP to copy it to one of your CF drives. It's a big file for a TRS-80, so it will take a few minutes to copy. This file is not in any standard format; it's just a quick-and-dirty implementation to enable the LS-DOS upgrade.

Expand the file onto a CF image. For the preferred configuration:


This will copy the image to device 1 (the primary CF card) image 1.

LS-DOS is now installed. Read the section on using LS-DOS with M3SE for further instructions.

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