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View Full Version : 3b1 ST506 hard drive(s) connection & operation questions



firebirdta84
October 11th, 2014, 12:30 AM
So, I've been learning a lot about the AT&T UNIX PC / 7300. I have acquired 2 and some spare parts, and am doing file transfer and disk formatting experiments with them.

None of them are the 3b1 model, they have no raised area under the display monitor, and only 1 MFM ST506 hard drive connector (20 & 34 pin pair) on the motherboard.

Unless I'm mistaken, I've heard that the 3b1 used 2 hard drives (as opposed to a single "full" height hard drive). So does this mean that the motherboard has a second 20-pin connector to accommodate the second drive's data connection?

And, will the 3b1 allow the drives to be formatted as separate drives, so they can be accessed independently, and copy files from one drive to another, or is it some other format where they both act as a single drive as far as the OS is concerned?

Thanks all,
-AJ
http://MightyFrame.com

lowen
October 11th, 2014, 05:05 AM
...

Unless I'm mistaken, I've heard that the 3b1 used 2 hard drives (as opposed to a single "full" height hard drive). So does this mean that the motherboard has a second 20-pin connector to accommodate the second drive's data connection?

The 3b1 had a full height 70MB (well, 67MB, but what's +/- 3MB?). There was a kit to allow two drives, but that kit's availability these days is pretty rare. I purchased one of those kits twenty years ago, and had modded a 3b1 to handle two half-height 70MB drives, but that unit is long gone. You can read more about that in the comp.sys.3b1 FAQ (at least I think it's still in the FAQ; you might have to find an old copy).


And, will the 3b1 allow the drives to be formatted as separate drives, so they can be accessed independently, and copy files from one drive to another, or is it some other format where they both act as a single drive as far as the OS is concerned?

It's UNIX, so you mount the second drive as a directory somewhere in the filesystem; unix and kindred OS's don't really have a concept of 'drive letters' like Windows does. Even with Mac OS, individual drives or disk images are mounted under /Volumes, they don't get a 'drive letter.'

This is an advantage; suppose you are running out of space on your personal home filesystem, and you're short of space on the root; you can make a filesystem on another drive, copy all your home stuff over to the new drive, then mount that drive as your home filesystem, and no programs need to be modified. I do this on my personal Linux and *BSD systems; the /home directory is actually a whole separate partition mounted on /home. That way I can do reinstalls of the OS without reformatting my /home. And I can put /home on a larger drive or even a RAID or an LVM volume group and expand it as needed.

Windows NT (including 2000, XP, Vista, 7, and 8.x) also allow this type of functionality. A partition can be mounted to a directory, it does not have to have a drive letter.

firebirdta84
October 11th, 2014, 11:26 AM
Thanks, lowen.

This is very helpful.

Also, David Gesswein also just shared this URL with me by email in response to this question:

A modification to the UNIX PC to allow 2 hard drives. Since it's a DIY and not a Kit, as you mention lowen, I wonder how they might differ.

http://www.kloepfer.org/hdinstr.html#socklay

Did anyone else do this modification, or one like it, back in the day?

lowen
October 11th, 2014, 01:54 PM
...
A modification to the UNIX PC to allow 2 hard drives. Since it's a DIY and not a Kit, as you mention lowen, I wonder how they might differ.

http://www.kloepfer.org/hdinstr.html#socklay

Did anyone else do this modification, or one like it, back in the day?

This is the modification I'm talking about; at one point you could buy a kit of parts that included the PAL mentioned in the article. It's good that this article includes the PAL equations; that was not distributed previously as far as I was aware (but again that's been over 20 years ago since I ordered the kit that included the PAL). Further edit: I actually performed this mod on my 3b1 back in the day, and it worked. But it was quite the project as I recall. Add the WD2010 and you get even better capacity available to you.