Compaq Portable II PSU - value of C13?

Jules Richardson jules.richardson99 at
Sat Oct 3 17:09:03 CDT 2020

On 10/3/20 4:34 PM, Jules Richardson via cctalk wrote:
> Hi all,
> Does anyone happen to know the value of C13 in a Compaq Portable II power 

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.

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