Seagate ST-225: Just Wow

A few weeks ago a Seagate ST-225 drive more or less accidentally landed at the OS/2 Museum. The drive is nearly 30 years old (manufactured in late 1986) and rather interestingly, this particular unit comes with a label declaring it as “Manufactured for IBM Corporation, Armonk, New York”.

Seagate ST-225 20 MB hard disk

Seagate ST-225 20 MB hard disk

It is a standard 20 MB PC/AT disk, CMOS type 2. It uses the ST-506 MFM interface. 5¼” half-height, loud, 3,600 RPM, 5 Mbit/s transfer rate, two platters, stepper motor, no auto-park… essentially first generation PC hard disk technology, but refined for mass production. There is some chance the drive started its life in an IBM XT Model 286.

The drive’s functionality was unknown and doubtful but could not be immediately tested because I was missing one little piece—a pair of ST-506 style cables. After sourcing the cables I hooked up the drive to a 25 MHz 386 board through a true blue IBM fixed disk and floppy controller (68X3815, Western Digital chips). Was it going to work?

The drive spun up but did not boot. It did however get as far as printing a boot error from the MBR. So not completely dead. An examination with Norton Diskedit showed that the drive still contained data (PC DOS 3.3 and a few applications), but lots of sectors were marginal (mostly but not entirely unreadable) and the 4th head could not read anything whatsoever.

The ST-225 lid

The ST-225 lid

Of course the trouble with MFM hard disks is that the data path is entirely analog and data written by one controller is not necessarily readable by another controller. And I had no idea what controller this drive was previously used with. Clearly one which used the same general format (otherwise nothing would be readable) but perhaps not quite compatible with mine.

Still, there was just enough readable data that with a bit of luck I could read a sufficient amount of the FATs and root directory to look around the drive. It had been last used around 1992 judging from the timestamps. With the 4th head delivering no data there wasn’t much that could be recovered, and the FAT and root directory sectors were flaky enough that even ‘dir c:’ only worked some of the time. The data was too far gone for SpinRite to do anything.

After a while I gave up on recovering the data from the drive, especially because I was sufficiently confident that there wasn’t anything uniquely interesting. I ran the Seagate format utility on the drive, changing the interleave from 3:1 to 2:1 in the process.

After the format I did a quick verify, simply reading back all sectors. Zero bad sectors were reported! The drive also came with an empty defect list sticker, but this was still surprising. Next I ran much a more aggressive verification in the Seagate format utility which tries 9 different data patterns (and takes far longer). After good 8 hours, the results were in: zero defects.

I installed DOS and a few utilities on the disk and the next day ran SpinRite for a good measure. Again, no problems found. Amazing.

The Seagate ST-225 has a bit of a reputation for uncommonly high reliability. And that is something which can be judged after 30+ years. Zero defects after 30 years is impressive, and that’s a fairly dumb drive with no sector remapping or anything of that sort. It was just that well made.

Seagate ST-225 label

Seagate ST-225 label

This is especially interesting (ironic?) when the ST-225 is compared with the original CMI (Computer Memories Inc) 20 MB drive built into the early PC/AT units. Those drives failed so often that CMI went out of business and IBM’s reputation took a serious hit.

It would be tempting to say “they don’t make them like that anymore” about the ST-225, but that’s something we’ll perhaps be able to say in another 30 years.

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10 Responses to Seagate ST-225: Just Wow

  1. ths says:

    Could this even be reformatted with RLL and interleave 1:1 with a better HD controller adapter?

  2. Michal Necasek says:

    1:1 interleave definitely, but that’s a function of the controller/system. With my current setup 2:1 is the optimal interleave.

    As for RLL, that depends on who you ask. Seagate says no (of course), but at least some people successfully used it. With a drive made in 1986 it’s possible that there’s no real difference from the corresponding RLL model. I don’t have an RLL controller at hand so can’t test. My guess is that it would work.

  3. Rich Shealer says:

    Did you try SpinRite before you low leveled it?

    In my experience the ST-225 didn’t do well when formatted as an RLL drive, but it may have worked better with the SMART RLL controllers that had their own BIOS.

    The 286 and 386 PC’s we built that used an RLL controller that relied on the computers BIOS drive geometry table. They were quite a bit less expensive than the smart controllers with a BIOS that allowed the user to enter their own values.

    We used to copy the motherboard BIOS and modify the drive geometry table to fit the newer drives we had. This was both to change heads and cylinder counts and change from the 17 sectors for MFM to the 27 sectors for RLL. We had to regenerate the ROM checksum after making the change. OnTrack had software with some drives that allowed us to access drives with a mismatched table, but I think we had issues with that with Novell servers and disk utilities so we avoided it.

    Eventually the BIOS was harder to change and the price of the smart RLL controllers had dropped and we used the smart controllers.

  4. Michal Necasek says:

    I did try SpinRite before reformatting, but it wouldn’t work because it basically couldn’t even read the root directory on the drive.

  5. Richard Wells says:

    ST-238R is the ST-225 set for RLL usage. Same exact drive mechanism, better QC: no bad sectors on the first couple of tracks and fewer weak spots on the rest of the drive. RLL took the open loop stepper design to its limits and made the drive susceptible to failure from heat or bearing wear. What I remember is some buyers would go the other way, purchasing the RLL qualified drive variant and placing it on a MFM controller for maximum reliability.

    If your ST-225 works the same as mine did, the drive after reformatting will continue to work for a few years before failing again. There will a number of progressively shorter failure followed by reformat cycles until the drive finally fails for good.

  6. raijinzrael says:

    Rich Shealer: Yes, older Ontrack drivers based in loading overlay from Config.sys had troubles with non aware OS disk drivers. These problems were fixed in newer Ontrack versions based in INT13H overlay loading via MBR, and updated disk drivers for these OSs (i remember drisk driver updates available for NT, OS/2 and Novell Netware). Ontrack itself comes with an updated Win3.1 FastDisk driver version for generic ST/IDE/ESDI controllers that is Ontrack overlay software aware.

  7. Esteban says:

    What is Norton Diskedit and what can you do with it? Can you create a drive image with it?

  8. Michal Necasek says:

    It’s what the name suggests, a disk editor. I think you can create a drive image with it but that’s not really what it was intended for.

  9. 8bitWarrior says:

    I had a few ST-225’s in various XT clones and a real 5150. Most required the data to be re written so that it stayed stable. They had issues with temperature change because the heads were attached to the stepper motor by a metal band that shrank or lengthened and the heads wouldn’t read or write to the exact spot the data was stored on the platters.

  10. Michal Necasek says:

    That’s good to know. Makes sense, the whole thing is a giant floppy drive in a box, a completely dumb device.

    I guess that’s why SpinRite was popular back in the day.

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