Assuming this is a hardware interleave (ie: physically different sector number ordering on the track): The loader is typically loaded "raw fast" by the boot, which is simply reading the sectors into memory, so once one is done, it can be immediately ready for the next one. It may therefore speed up the boot process slightly to put these sectors with 1:1 interleave. The remainder of the disk is "application area" and the amount of processing required between sectors is indeterminate, but you can be fairly sure that most of the time there will be some gap between sector requests, so it makes sense to interleave these. If it's software interleave (like CP/M does with it's XLT table), then the reason may be more basic - the loader may not include enough smarts to perform the local to physical sector translation, hence boot tracks have logical=physical. I doubt that interleave will affect the functionality of either area other than speed. Regards, Dave -- dave04a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.parse.com/~ddunfield/museum/index.html