Re: HP 9135A, compatible hard disk drives
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On 2020-06-05 11:29 p.m., HP75_8687
Unfortunately my HP 9135A (large form factor first desktop 5MB
HDD/ 5.25" FDD combo drive) has a broken hard disk. (head crash,
definitively no chance to recover).
The HDD is a Seagate ST-506, 5MB; that is the first ever 5 1/4
inch desktop hard disk drive. ST-506 is also the name of the
These HDDs are difficult to find today (has anyone got one? I'd
love to buy it.)
Now the question is whether it could be replaced by
another HDD that is fully downward compatible.
Seagate's second HDD was the ST 412 , 10 MB (built into the 9134B,
Unfortunately (from my perspective :-) ) Seagate introduced a new
interface for the new HDD, not surprisingly called "ST-412
HDDs that are designed for ST-412 interface are more common and
easier to get, like the ST 225 (20 MB).
What are the differences between the ST-506 and the ST-412
interfaces? It seems they are tiny, but is is there some
More concrete: Should an ST 412 or ST 225 work at an ST-506
controller, only slower? (ST-412 introduced kind of a burst mode).
If it should turn out to be impossible to get an ST-412-type HDD
to work at the ST-506 inside my 9135A, I'd like to know if there
are pure ST-506 drives other than the ST-506 itself, and would be
happy if someone had a tip where to find.
I have to admit that I am not totally sure that a ST 412 won't
work in a 9135A (then reduced to 5 MB capacity, of course). I have
a spare drive that I tested in my 9134B a few weeks ago, it worked
fine. Now it doesn't work in my 9135A (throws "DISC" errors, when
I try to INITIALIZE). But theoretically something could have
happened to the drive meanwhile ... unlikely, but possible.
Paul suggested that there might be next to no difference between
the controller boards of a 9134B and a 9135A. There has never been
a 9135B, B versions (featuring the 10 MB ST-412) exist only as
9134 (HDD only) and 9133 (HDD/3.5" FDD). A 9135A probably is too
old to know about the newer standard ... but who knows ... there
are a few jumpers on the board.
Has anybody got a copy of the service manual for the
9135A? I could not even find it mentioned anywhere.
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