Hi, Thanks for the replies. I've probably seen some of the web sites mentioned as I have downloaded various manuals and documentation for the system. The processor board has the provision for 1K EPROM, which isn't installed. I'd assume it's for a 2708 device. Unfortunately I cannot program these devices, so I can program a 2716 and do some mods to the processor card to make the 2716 work and show only the 1st 1kbyte. In my spares I have a few Dynabyte and Microbyte RAM cards (both static and dynamic), an old MITS 8800B CPU card (which needs some serious TLC), a spare ZPB processor card, some weird S-100 Inc 4K EPROM card which looks like it can take 8 x 512byte, or 4 x 1k or 2 x 2k EPROMS, a Vector Graphics ZCB processor card, and a few S-100 blank prototyping cards and a 4-slot S-100 mainboard. I can wire-wrap up one of the proto boards as an EPROM card if I need more and run the DOS all in silicon, if this is possible. So, if push comes to shove I can modify and use one of my 8080/85 debug/monitors and let it run on the Northstar. I guess the hardest part is getting a set of drives that will run on the AD3 card, along with the necessary diskettes. I rechecked the disk controller card and it is clearly labelled "Micro Disk Controller MDS-AD3", which makes it the double-density diskette controller. I do have another disk controller card, by Delta Products, that has a 1791 FD controller chip on it, but I have no doco for this board. However, the first thing I need to do is clean-up the system, blow out the dust, fix the blown caps and then go through the downloaded documentation that describes how to test/verify the various boards are operational. Again, thanks for you replies and I'm going to join them into a single document for reference and also go to the various links you have supplied to see if I can get more information. regards river