Hi Bob The boot loader for my Nicolet is similar in that it over writes itself. It fits into about 15 words so it is quite easy to toggle in. They even took advantage of the 'don't care' fields in some instructions to take advantage of minimizing switch changes. Even the memory location is chosen because it is has bits that fit well in adjacent instructions. It is quite remarkable that they can squeeze so much into so few instructions. I have written a boot loader that I use to transfer data to and from an H89 ( Heathkit ) computer that takes about 52 bytes. Most is com port initializing. It was nice when the hardware was jumper configured. The loader would be much smaller. The loader is such that I can send it by email and someone can bring a H89 up from scratch. They just need a couple of blank 10 sectored disks and my code. Later Dwight