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Thread: 3.5" floppies won't exchange between PUTR and PDP-11 - except one...

  1. #1

    Question 3.5" floppies won't exchange between PUTR and PDP-11 - except one...

    In another thread, I chronicled my adventure getting a 3.5" floppy drive hooked up to my PDP-11/23+.
    It now looks to the system (RT-11 5.04 and TSX+ 6.50) like an RX33 with nearly 2400 blocks. So far so good.
    I had a 720K disk mixed in there, and when I put it in the PDP-11, FORMAT balked and warned me it was an RX50 disk. So the controller can "tell".

    I can format DS/HD disks on the PDP-11, and read and write to them... but when I put them in the WinXP box running PUTR, they won't even read the directory. PUTR is correctly set up for RX33 type, RT11 filesystem.

    In fact, most of the used disks won't even format on the PC, let alone read/write. OK, so they're old. Found some more disks (a new-old-stock box of Memorex DS/HD) and they will format on the PC or on the PDP-11, but they can only be formatted, read or written by the hardware that did the format!

    Figured it might be drive head misalignment since this hardware is all old. I tried another 3.5" drive in the PC after cleaning the heads and it behaves exactly the same way.

    What's really strange is that just ONE used Verbatim DS/HD disk can be read and written between systems, just like they all should.

    Any ideas what's going on here? Do I need two new drives? Or just go back to RX50 5.25" drives?

  2. #2

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    I noted that a 3.5" 1.44 MB floppy is actually an RX23, and PUTR's instructions says it supports RX33 on 5.25" 1.2 MB media. Hmm.

    But the RQDX3 controller definitely emulates an RX33 on the 3.5" HD media, which has been covered in a couple of previous threads here.
    Maybe I'll try running PUTR in RX23 mode tomorrow...

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    Remember that XP "abstracts" the floppy hardware. Try running it under Win9x or DOS.

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    RX33 is in fact a 5 1/4" drive which have 360RPM. I don't know how the PDP-11 formats the "rest" of the track when you attach a 3 1/2" drive which hs 300RPM. WindowsXP will probably bark as there are not 18 sectors per track or something unexpected. Here is some more information http://avitech.com.au/?page_id=645. As Chuck said, try an older Windows/DOS. Your only Diskette that works might have the "rest" being formatted so Windows thinks it is a 1.2Mb HD drive.

  5. #5

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    Thanks for the info! I've read all of Mal's pages and find them very useful.

    I can try booting the PC to DOS (if I can find a disk!)... but why does the OS matter to PUTR? Please clarify further if you can
    PUTR opens in a CMD window which I thought *was* MSDOS? I'm mounting and formatting the floppy exactly as the 2001 instructions show.

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    Quote Originally Posted by cbscpe View Post
    RX33 is in fact a 5 1/4" drive which have 360RPM. I don't know how the PDP-11 formats the "rest" of the track when you attach a 3 1/2" drive which hs 300RPM. WindowsXP will probably bark as there are not 18 sectors per track or something unexpected. Here is some more information http://avitech.com.au/?page_id=645. As Chuck said, try an older Windows/DOS. Your only Diskette that works might have the "rest" being formatted so Windows thinks it is a 1.2Mb HD drive.
    Many 3.5" drives (particularly my favorite Samsung SFD-321B) can be configured for 360 RPM/1.3MB operation. I run into this all the time when dealing with old Japanese CNC gear. This is the so-called "1.6MB" unformatted mode, as opposed to the "2.0MB" 300 RPM one.

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    I was not aware that the SFD-321B can be configured for 360RPM. How do you do that? Would be very interesting to test it.

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    SFD-321B OEM manual

    It's a very flexible drive--one word of caution, however: the units with the "naked" connector don't seem to have the same options as the more common ones with the shrouded connector.

    The drives themselves should still be quite plentiful--Samsung OEMed a ton of them.

  10. #10

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    Thanks for the Allbootdisks link. I made an MS-DOS 6.22 floppy and booted from it. But the only drives it "knows" about are A: and the CD-ROM.
    Where is C: ? It's definitely in the BIOS.

    I'm trying to dredge out more memories from early '90's... didn't think I had to tell MS-DOS that there is a hard drive sitting there??

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