Special considerations

There are several differences between Tape Update and the other update functions:

• Tape Update copies tape blocks from one device to another device, with the changes that you specify. If you make a mistake, you still have the original data on the input tape as a backup.
• You can copy and update several consecutive tape files by specifying the number of files that you want to update. To update all the files until a double tape mark or an EOV label is reached, specify EOV in the Files entry field.
• When you use Tape Update, both the input tape and the output tape are backspaced to the nearest tape mark (if they are not already positioned immediately after a tape mark).
• Blocks are copied dynamically, as you move through the files. For example:
  1. You select Tape Update and specify an input tape and an output tape. You accept the default (to update only one tape file).

     One screen of data is displayed while copying to the output tape.

  2. You move forward 50 blocks.

     The first 50 blocks are written to the output tape.

  3. You move backward 10 blocks.

     Both tapes move back 10 blocks.

  4. You change the current block (block 41).

     The changed block is written to the output tape.

  5. You end Tape Update.

     All blocks from block 42 to the end of the file are written to the output tape.

• Because blocks are copied dynamically, always make your updates in ascending order, starting at the beginning of the file. Simply scrolling backwards does not cause any updates to be lost. However, if you update a block (with a lower block number than previously changed blocks), all previous changes to blocks with a higher number are lost. Also, if you rewind the tapes, all updates are lost.

  For example, if you change block 50, then change block 40, then end Tape Update, this is what happens:

  1. Blocks 1 to 50 are copied.
  2. The changed block 50 is written.
  3. The changed block 40 is written.
  4. Blocks 41 to the end of the file are copied. The change that you made to block 50 is lost.
• Throughout the update process, the two tapes should remain in synchronization. If an input∕output error causes the tapes to get out of synchronization, use Tape Rewind (option 4.15.5) to rewind the tapes and restore synchronization. (Note, however, that rewinding the tapes causes all previous updates to be lost.)

Tape Update does not support ASCII conversion.