Compaq Portable II PSU - value of C13?

On 10/3/20 4:34 PM, Jules Richardson via cctalk wrote: Additional question, does anyone know the nature of the ST506-IDE bridge in these machines? My hard disk is a Miniscribe 8212, which I think has two heads and 615 cylinders (at 17spt), giving ~10MB formatted. However there's a sticker on top of the drive saying "type 1" - according to a Compaq reference I found, that's for a drive with 306 cylinders and four heads (and again 17spt). It's still ~10MB, but obviously a completely different geometry. So, does the Compaq bridge do translation between logical and physical geometry (and so the bridge presents it as a four-head drive even though it's not)? Or has someone perhaps put a drive from a different system in there at some point (and so the "type 1" refers to that unknown system's BIOS drive table)? The Compaq BIOS table has an entry as type 15 which is all zeros, so that's possibly some sort of "user defined" option, although I don't know if it can store the parameters in NVRAM and treat it as a bootable device, or if it could only be accessed via floppy boot. I have no idea what the original stored system settings were - the battery's long-gone.