The jobs are submitted and then wait in a queue, until a tape device is free. At that time the operator will mount the tape and allow your tape job to process. Results are returned to you through an electronic mail message. The copyt utility asks you a few questions about the tape format and the operation you want to perform, then it builds a shell script for you and submits it using tapereq. The results from copyt are returned to you by electronic mail.
Density is measured in characters per inch of tape.
The choices are 1600 and 6250 characters per inch. This also might be called the Record Size or Logical Record Length. Magnetic tapes may be labeled or unlabeled. Labels are actually recorded at the beginning of the tape and follow an ANSI standard. Most blocked tapes are unlabeled.