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Format with write protect on...

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    #76
    Originally posted by Agent Orange View Post
    I'm a little slow on this but I'm starting to catch on. I've been running my 1000SX for over 35 years and just never seen or heard of anything like what you're going through. Seems a bit odd to me.
    It is an odd thing; I will give you that. The funny thing is that I almost remember running into this with my original Tandy 1000 back in the 80's.

    Comment


      #77
      Originally posted by alank2 View Post
      It is an odd thing; I will give you that. The funny thing is that I almost remember running into this with my original Tandy 1000 back in the 80's.
      I used to know a lot about this - I wrote a fair number of Lifeboat's CP/M formatter programs. By my memory doesn't have parity, let alone ECC, so some bits may have flipped over the years.

      The uPD765 and clones are pretty intelligent compared to a WD17xx and clones. As an example, to format on a 765 you tell it "I want X sectors of Y bytes" (for restricted values of X and Y). On a 17xx, you create a bit image of the track, pass it to the 17xx and it FM/MFM encodes it and writes it to the disk.

      This means that formatting with a 765 is a lot easier, but you can't do low-level tricks like create Datapoint double-density disks (they're RX02-like, with single-density headers and double-density data).

      The drive itself has no idea about write protect status, other than passing it to the controller - old drives like these and ST506-type hard drives have no concept of "command reject" because they don't have any commands to reject - they're just state data and raw serial bits. So it is quite possible for a badly-coded format utility to think it has sucessfully formatted a drive until either it or some other disk I/O tries to read the disk and fails. In 8080/Z-80 and real-mode 80x86, there's no need to use OS/BIOS facilities to format disks - you can just talk to the hardware directly.

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        #78
        It seems to me that if I attempt to 'write' to or 'format' a 3.5" or 5.25" floppy in my 1000SX, and the write tab is closed or there is a protection tab in place, DOS lets me know. It ain't gonna let me do it.
        Surely not everyone was Kung-fu fighting

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          #79
          Originally posted by Terry Kennedy View Post
          The drive itself has no idea about write protect status, other than passing it to the controller - old drives like these and ST506-type hard drives have no concept of "command reject" because they don't have any commands to reject - they're just state data and raw serial bits.
          Are you saying that the drive itself does not obey its own write protect sensor? I wondered it was a fail safe thing like that which prevents the disk from actually being written to in this case. It goes through the motions like it is formatting.

          Comment


            #80
            Originally posted by alank2 View Post
            Are you saying that the drive itself does not obey its own write protect sensor? I wondered it was a fail safe thing like that which prevents the disk from actually being written to in this case. It goes through the motions like it is formatting.
            I believe that on at least some drives it is just advisory and sent to the host. However, the Teac FD55G Technical Specification says that it does obey the sensed write protect status:

            ((6) WRITE DATA input signal (a) Pulse signal to designate the contents of data to be written on a disk. The pulse width should be 0.07 ~ 1.1μsec {at high density mode) or 0.07 ~ 2.1μsec (at nonnal density mode) and the leading edge of the pulse is used. (b) This signal is ineffective while either of the following condition is satisfied. i) The WRITE GATE signal is FALSE. ii) The WRITE PROTECT signal is TRUE.

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              #81
              Originally posted by Terry Kennedy View Post
              I believe that on at least some drives it is just advisory and sent to the host. However, the Teac FD55G Technical Specification says that it does obey the sensed write protect status:
              Another example of a drive that 'plays safe' is the Tandon TM100-2. The circuit diagram in the SAMS Computerfacts for the Tandon TM100-2, shows that an activated write protect switch:
              * Prevents the read/write heads from being activated; and
              * Stops an erase from happening; and
              * Asserts the WRITE PROTECT signal on the cable.

              Comment


                #82
                I've never run into a drive with a write-protect sensor that doesn't automatically inhibit writing. Perhaps some oddball Apple II drive, but not for a standard SA-400 interface drive. If you know of one, please point me at it. One reason for this behavior is that should power fail or otherwise glitch on the host side, the protection for the media will be absolute.

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                  #83
                  Just to make sure it wasn't a PC-DOS "anomaly" I tried the write-protected-format on my DMA-less 1000 HX using Tandy DOS 3.3, and it detected the disk was write protected at the start of the operation, as you'd expect on a normal PC.

                  I guess I need to lug the EX out of the closet and try it. If Tandy's version numbers are to be trusted it should have the same version of the BIOS as the SX. (An SX of course has the DMA controller built-in, so if this is a DMA-less-code train-specific bug you wouldn't really be able to trigger it in an SX.)
                  My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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