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Unreadable copies

If DiskDupe produces disks without reporting errors but some of the disks are unreadable there are several possible causes.

DiskDupe has several CRC checks built into it. Every track of the image file has a CRC, and there is a CRC for all of the tracks in the image, so you will find that if one bit of the image is changed in the data area then it will be rejected by our software ("Error 908, Image file corrupted"), so if there were a bad spot on your hard drive we would catch this.

DiskDupe also does a CRC check of its own code loaded in memory ("Error 906, Code Memory Corrupted") and a CRC check of the buffers used to store the image while transferring it to the diskette ("Error 907, Buffer Memory Corrupted").

When DiskDupe is run with "Verify" set to "Always" then every bit written to the disk is read back and compared to the original image and because of the above mentioned CRC checks it is not possible for the data to be written to the floppy with a different bit content from the image file.

Despite all of this checking it is possible for data to get corrupted when read from the floppy controller if there is a DMA problem causing a master to be read incorrectly. Running Drive Test ("Diagnostics") in DiskDupe will catch this and report either Error 205, Bad DMA, or Error 301, Bad Compare. Try running Drive Test to see if errors are reported on this machine.

  • If Drive Test passes then take some of the unreadable diskettes and compare them to their corresponding master disks or images using DiskDupe with the drive that the copies were made in and on other drives as well. Typical error messages that will come up are Error 202(Bad Address Mark), Error 204(Record not Found), and Error 207(Bad CRC). (If DiskDupe were to report an error 301(Bad Compare) reading one of these copies then this would indicate a hardware problem (most likely a DMA conflict) and also that the diskettes were copied with the compare option turned off in DiskDupe.)

If the bad disks are readable in the drive that produced them but not readable in other drives:

  • Poor drive alignment. This is probably the most common cause. If the diskettes are consistently unreadable in most drives except the drive that they were written on then the alignment of the drive used to make the copy is questionable. Usually such a diskette will be unreadable starting with the first track (i.e. cannot read the directory) on other machines. Check the alignment using DiskDupe Pro or AutoPro.
  • Poorly positioned track zero sensor. If the track zero sensor is positioned incorrectly then the drive might be able to produce diskettes that have the tracks in the wrong place on the diskette. Usually such a diskette will be unreadable starting with the first track (i.e. cannot read the directory) on other machines.
  • Copy drive is passing marginal diskettes. This problem is most common with double speed drives, especially Y-E Data 2X and 2XSDS drives. Diskettes that spin at double speed produce a stronger read signal than at regular speed so it is often possible to read a marginal diskette at 2X but not at 1X. Diskettes with these defects will often be readable on the first tracks because their errors (usually due to drop-outs in the media) occur randomly on the diskette. This problem is most obvious when poor quality media is used. Try reducing the number of retries that DiskDupe allows when comparing the disk to zero by using the /retries# command line switch (i.e. call up DiskDupe by typing: DISKDUPE /RETRIES0 from the Dos prompt. This setting gets saved in the DISKDUPE.DAT file so it does not need to be set every time. The default number of retries is two. This command line switch is only supported in version 4.09 and above and only in the Pro and AutoPro versions.
  • Disk type is set incorrectly in DiskDupe. This problem can be avoided by leaving the disk type set to "Auto" in DiskDupe. For example if you are making disk-to-disk copies of 1.44Mb disks with the disk type set to 1.2Mb then DiskDupe will read the master disks as it were a 1.2Mb diskette (ignoring the last three sectors of each track). The disks produced will be completely unreadable (fail on the first track with a "Record not found" error).

It the diskettes are not even readable on the drive that wrote them:

  • Dirty Drive heads:
    Before checking anything else make sure that the heads on the drive are clean because dirty heads are unpredictable.
  • Poor media quality:
    In this case the bad disks will show errors on various tracks. If the diskette quality is poor then the diskette will not hold its signal well over time. Use only certified diskettes with a clipping rate of at least 60%. For best results use blank media and format them as you copy to them using DiskDupe with "Format" set to "Always" in the Setup menu.
  • Drive cable is loose:
    If the drive cable connector is loose and pins 32, 33, and 34 are not connected and the rest are, then DiskDupe will format, write and verify disks with compare on, but the disks will be bad. It will also format the disks even if they are preformatted.

    Pin 32 is the pin that selects which side of the disk gets written to. If it is not connected then all of the data will be written to and read from only one side of the disk. When copying the disk DiskDupe reads back the information that it writes for each track immediately after writing it and thus reports no errors despite the fact that all the data is being written to and read from only one side of the disk. For each track the data for the first side gets written to and read from the first head and then the data for the second side gets written to and read from the first head again.

    If these disks are compared in a separate pass after duplication then DiskDupe will report and Error 204(Record not Found) on the first track since all of the side 1 data has been overwritten by the side 2 data. Drive Test will report the same error.

  • Diskette has not been removed from drive after copy:
    DiskDupe gets its speed by bypassing Dos and the BIOS of the computer. In doing so Dos is left in the dark with regards to the changes that occur to the diskette while the DiskDupe software is running. This often leads to strange results when a directory command is tried immediately after exiting from DiskDupe. If the diskette is removed from the drive and a [Ctrl][C] is typed before reinserting the diskette then Dos should then recognize that the disk in the drive has been changed and give an accurate response to a DIR command.