Brad> [I sent this on monday but it seems to have been lost; sorry if Brad> it's a dup] Brad> I have a dumb question about rx01 image files used by simh. Brad> I used "copflp" (by John Wilson - thanks John!) to image a box Brad> of rx01 floppies. Brad> I then put the images on pc and used simh and I can see them Brad> fine with rt11 running under simh (i.e. "att rx0 image.dsk") Brad> But an old program I have which will read rt11 images does not Brad> see the directories. I am confused because it works fine with Brad> mscp image files that I connect to simh via an ra device (like Brad> an rd32). Brad> What's the difference between rt11 ra image files and rt11 rx01 Brad> image files? I would think the rt11 volume and directory info Brad> would be in the same place (but it seems I'm wrong). Brad> I tried skipping track 0 by offsetting 128*26 bytes, but that Brad> did not help. It looks like 128*25 might be a better offset Brad> for floppies. Brad> what am I missing? Here's a guess -- I don't have the right sources at hand to make a certain determination. Some floppies use interleaving. RX50, for example. Looking at the RSTS RX01/02 driver, I see that it supports interleaving; what isn't clear to me without a lot more digging is whether that applies to RT format floppies. If it does, then the translation looks like this: 1. Track 0 is skipped, so logical track 0 is physical track 1/ 2. Within a track, logical sector numbrs 0-12 correspond to the even numbered physical sectors, 13-25 the odd numbered physical sector. So logical sector 13 is physical sector 1. 3. In addition to (2), sectors are skewed. After doing the interleave calculation in (2), add 6 * logical track number to the physical sector number to get the final value. You might give that a try... paul