A regular 3590 tape when used in a 'B' drive capacity is 10GB, extended tape
capacity is 2x or 20GB.
A regular 3590 tape when used in a 'E' drive capacity is 20GB, extended tape
capacity is 2x or 40GB.
A 3590 'B' drive can read / write both tapes.
A 3590 'E' drive can read / write both tapes.
A 3590 'E' drive can read tapes written by a 3590 'B' drive.
A 3590 'B' drive can NOT read tapes written by a 3590 'E' drive.
A 3590 'E' drive can NOT write to tapes ALREADY containing data written by a
3590 'B' drive.

Cautions.
Mark all tapes as full if you change drives from 'B' to 'E'.
Check your device classes for capacity settings.
In the 390 or Z/OS world there are parmlib settings you need when changing
drives.