Compaq Portable 286 and Portable III - IDE drives?

jim stephens jwsmail at
Fri Mar 3 16:07:07 CST 2017

On 3/3/2017 1:08 PM, Fred Cisin via cctalk wrote:
> On Fri, 3 Mar 2017, Jules Richardson via cctalk wrote:
>> Just checking here, as someone told me that this is the case, but do 
>> the Compaq Portable 286 and Portable III take stock 40-pin IDE hard 
>> drives? I just wanted to make sure that they weren't expecting 
>> something that might be a bit non-standard before I go trying to find 
>> modern replacements for a pair of failing disks.
> I think so, but I also think that Compaq's IDE was before it was 
> completely standardized, so there might be some glitches.
The bios has a table that you can dump out as usual, which is unique to 
the Compaq portable 3.  Other than that and having to modify the table 
to accommodate the new drive geometry, I had no problem.  It was 
possible to run 200mb drives, as all of min have such on them.
>> Assuming that an enormous modern(ish) drive is OK, are there any 
>> other gotchas involved in configuration and formatting? Obviously I 
>> don't need a partition bigger than a few tens of MB, but perhaps 
>> there are things to keep in mind when fitting a drive that's most 
>> likely to be getting on for a thousand times the capacity of the 
>> original.
> 1) If you are going period OS, get Compaq MS-DOS V3.31.  Anything 
> prior to that is limited to 32MB per partition.
> 2) You may want to use a "disk manager overlay" to be able to use 
> specs other than the BIOS ones:
I ran Pick and other systems other than DOS and modified the roms to 
have new geometry.  The entries up to #13 match the IBM.

I think #4 and #20, IIRC are the common ones you see as evidenced by a 
sticker on the case behind the plasma display.

The Roms are simple to modify, if you know that they are Even / Odd for 
a 16 bit total width.  you will have to figure out a new checksum and 
modify the last byte of the rom to come up 0.  Again, if i recall you 
need to make the overall sum come up = 0.

I always read the rom from high memory into ram and wrote a simple loop 
to add up the checksum in AL.  The play with the last byte till you get 
it back to 0.

I ran Pick R83 on all of mine, with an 8way and streaming tape card in 
the expansion bay.  A very nifty 286 or 386 8 user system for demos back 
in the days


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