Are the ST506 and ST412 specs different and incompatible?
I've seen these two specs used together, separately, and in a few documents,
interchangeably. The bubble repair document on Ira's site uses ST506, but the
Seagate ST-4038 is specified as ST412 MFM, not RLL). The drive seems to meet all the
other requirements for the old (large) controller, in that it has 5 heads and 733
Can anyone shed light on this?
> Can anyone shed light on this?
See Frank Durda's page at
WGCR Internet Radio
1 Peter 4:11
Thanks, I read it and didn't see the answer to my question. The ST412 was an earlier
Seagate drive, and the interface for it also is refered to as a "standard". But is
it different from the ST506 in an incompatible way?
Guess I'll look for old-timers at Seagate. They still post the specs and connection
info for these old drives on their web site, which I think is great.
>I am contemplating replacing the 5 MB disk in my TRS-80 HD
>with a 31 MB disk. I looked at the information on Ira's site
>concerning this, and came up with a question.
>Are the ST506 and ST412 specs different and incompatible?
Compatible to a point.
>I've seen these two specs used together, separately, and in a
>few documents, interchangeably. The bubble repair document on
>Ira's site uses ST506, but the Seagate ST-4038 is specified
>as ST412 MFM, not RLL). The drive seems to meet all the other
>requirements for the old (large) controller, in that it has 5
>heads and 733 cylinders.
>Can anyone shed light on this?
All the early drives were pretty dumb and the formatting and setup
utilities did all the work. In modern drives the drives take care
In the ST506 you are limited to 70MB and heads 0 thru 7.
You also set the value for the track on which write-precompensation
Write-pre comp is when you modify the signal to take care of
bit-shifting that occurs on the inner tracks were one bit can
affect an adjacent bit. Since identical magnetic forces repel
the bits want to shift away - and the pre-comp change the
timing/spacing so this doesn't occur. That's also something you
see in coated media that is relatively soft - which was the norm
for the old drives.
In the ST506 there is a line that is toggled when it is time
to use write-precompensation.
In the ST412 drives they handle write-precompensation internally.
The line that was used for write-precomp now becomes a head-select
Normally you select heads 0 thru 7, but on the ST412 when you
toggle the old write-precomp - now head select, when you select 0
it is head 8, and 1 is head 9 and so on until you get 15 heads.
So you can used ST412 drives on an ST506 interface >>IF<< you only
format the first 8 tracks - heads 0 thru 7.
We used to put the ST4096 Seagate in the Model 16's to get 70MB.
The ST0496 is a 77MB drive with 9 heads. But if you tried to
format 9 heads using the standard controller - which used
the WD1010 controller chip that only knew about 8 heads - once
you went to head 8 [the ninth head] and since that was
write-precomp, you actually wrote over track 0. That is not what
you want to do.
To sum up:
ST506/ST412 is seen quite often. Pure ST605 interfaces were
used only in the early days. They are virtually identical except
for the write-precomp line becoming head select. You can use
ST412 drives in ST506 but DO NOT format for more than 8 heads.
You can also set write-precomp to the maxium number of cylinders
when using an ST412 on an ST506 controller - because the ST412
handles write-precomp intenally.
You used to have to know all this stuff if you used other than the
drives speced by the factory. The old 16's had a Tandem drive that
would fail in strange ways and would lose on head or the access to
one. I'd take the standard ST225 - the 1/2 height 5.25" and put
those in the 16 - or if I just needed to load the data from the
Bermoulli backups so I could xfer the data from the 16, I'd just
route the cable out the back and have the 225 on the table for the
time it took to transfer.
Bill Vermillion - bv @ wjv . com
Without going into too much detail, the Seagate ST506 was a 5.? megabyte
full height MFM hard drive. I am pretty sure this was actually the first
Seagate hard disk drive. I think the drive geometry was something like
153cyl x 2 hds. This was a very simple and slow drive.
The Old Apple 5 Meg profile actually used an ST-506 mechanism with an Apple
manufactured logic board.
The ST412 was a full height 10 meg (306cyl x 4 hds). The ST412 was actually
one of the 10 meg drives supplied with the original IBM XT. The drive was a
bit more intelligent than the ST506!
The links to Frank Durda's website in other posts is excellent, pay
attention to the information about the drive activity light and write
I used to run an old 5 meg drive chassis, with a Micropolis 1335 70 meg
(similar to the 1325) in place of the Tandon drive on my 16A..
"Larry Fosdick" <larry_...@hotmail.com> wrote in message
Seagate has all their drive specs on their web site, so you can actually look at the
specs for the original ST-506 and ST-412 drives. The funny part was they lumped the
two specs together in their glossary, which was why I posted here. There had to be
some differences, or why have two specs.
"Bill Vermillion" <b...@wjv.comREMOVE> wrote in message news:HBq13...@wjv.com...
>Thanks for the replies, Bill and David. You've cleared this
>up nicely. It's been so long since I've used MFM drives (back
>when I had a Tandy 1000), that I just wasn't sure about the
>differences. I also wrote to Seagate tech support about this
>question. They thought I'd be okay, too. I'm planning to use a
>Seagate ST-4038, which only has 5 heads and 733 cylinders, which
>falls under the limits for the ST506 interface.
Just to clarify - you can run drives with more than 8 heads - but
you throw those extra cylinders away by specing the drive as having
only 8 or fewer heads.
If your drive has 5 heads then it has 3 platters and 5 sides are
used for data and the 6th side is for servo control.
>Seagate has all their drive specs on their web site, so you can
>actually look at the specs for the original ST-506 and ST-412
>drives. The funny part was they lumped the two specs together
>in their glossary, which was why I posted here. There had to be
>some differences, or why have two specs.
As soon as the 412 interface appeared saying that the drive
had a ST560/ST412 or just 506/412 interface became common for the
I remember when someone was selling extras ST506 drive - not
interfaces but the real modem number ST506 - at a bargain price
of $999. Those were normally in the $2k range.
The boxes they came in were over 2 feet - probalby 30" x 30".
You open the box and there were springs going from the 8 corners
of the shipping box - to a small box suspended by those springs.
In side that box - carefully packed in foam - was the ST506.
These drives could only take a bit less than 1G shock when shipped
that's why the elaborate shipping containers.
In thses days with the 2" lap stop drive with their glass platters
able to sustain 100G shocks when running the old days look
had hardware that was below 'crude'.
My first home computer arrived a bit over 25 years ago - and I'd
not wish the problems we had then on anyone who has experienced
only more modern machines.
>Without going into too much detail, the Seagate ST506 was a 5.?
>megabyte full height MFM hard drive. I am pretty sure this was
>actually the first Seagate hard disk drive.
Actually i twas more than the first Shugart hard disk drive, it
was the first 5.25" hard drive by any manufacturer. [Bill Shugart
later sold his company to Xerox and started the Seagate line]
I also have a 5.25" floppy from Shugart that is from the first
engineering test run [ pre production ] of the first 5.25" floppy
ever made. The control board snaps off with phosphor bronze
springs and the serial number is handwritten in the 1600 range.
Often in those days serial numbers would start at 1000, so this
could have been the 600th floppy producted, if not being among the
first 1600 produced makes it a rarity. Not worth much expect for
Hm - days like this when I think back makes me think I've been
using these 'wee beasties' far too long.
>I used to run an old 5 meg drive chassis, with a Micropolis 1335 70 meg
>(similar to the 1325) in place of the Tandon drive on my 16A..
I put the 1335 in my 6000. My 16 - had externals with two
floppies. Serial number on that - if you strip the leading model
numbers from the serial number it shows it was about 700-800th
built. Got it from an RS store on as/is where/is when the newer
model came out. So it was one of the orignal store demo units. I
actually was running a pair of Rodime 35MB externals on the 16 as
a Unsnet news node back in '86.