Most Unix systems will look for an environment variable named TAPE and use that. If not, you will need to know which device you are using. Unix creates multiple device files for the same tape device to handle different types of functions. NR means that the tape will not rewind when you close the tape device, this is needed if you want to place multiple files on a tape, one after another. NS means non-byte swap and is used by default, S is the byte swap device and is used when making tapes for machines such as sun systems.
V allows variable block sizes to be written and requires a special tape device.
Density is the type of tape device you are using and helps determine maximum size. Hopefully this won't have to happen but you need to be prepared. However, in practice something always arises to require a restore. If you have multiple levels of the file system restore will restore the files in reverse order of when they were dumped. To restore just one file, use the restore command in interactive mode.