I’ve been sidetracked by another project but I’m getting back to the below LSI11 simulator. The simulator code loads and runs the first 256 words from whichever disk image is attached to the simulator. No RT-11 disk image I’ve used will boot, and I suspect that it’s because the simulated RX01 isn’t faithful enough that an unmodified RT11 disk image would work (not to mention, the address of the disk controller isn’t the same as the RXV11). I’ve also tried to disable the LTC interrupt within the simulator code because, from my own experience with RT-11, it won’t boot with the LTC enabled. I was able to locate and correspond with the original author, and he doesn’t recall creating custom disks or disk images. Hmmm. So, I was hoping someone could point me to a listing of what the on-disk boot block code on an RT-11 floppy might look like. It might be buried in an RT-11 manual somewhere, but Googling isn’t really giving me what I’m looking for. It’s like looking for a disassembly of the MS-DOS boot sector. Thanks! Rich -- Rich Cini http://www.classiccmp.org/cini http://www.classiccmp.org/altair32 On 8/15/20, 8:46 AM, "Richard Cini" <rich.cini@gmail.com> wrote: All – I’m cleaning out my shop (I will have a “to go” list at some point) and going through magazine articles I saved. One peaked my interest, from Circuit Cellar (7/1996) by Robert W. Meister, was an LSI-11 simulator. I liked working on my Altair32 project, so I thought this would be good to play with. I was able to find the original simulator code from the article and it compiles under MS-DOS with only minor changes, but it has certain compromises regarding the hardware memory addresses and return codes that require it to use a custom RT-11 boot diskette (it has a custom DX.SYS, I’m guessing). I’ve done quite a bit of Googling about the simulator and the author (who worked for the NASD at the time he wrote the article), but haven’t come up with much additional information. Yes, I could easily use SIMH instead, but this is a fun project to work on to keep the mind busy. I guess I have four options: move memory around and see if the default DX.SYS will work; write a custom DX.SYS and make a new image using SIMH (way beyond me); continue to hunt down the author and see if he has any of the original files; give up and just use SIMH. If anyone is interested, I can send a PDF of the article. It’s actually a neatly-written program, and the ODT works fine. Rich -- Rich Cini http://www.classiccmp.org/cini http://www.classiccmp.org/altair32