From: Robotics (Autochangers, Jukeboxes, Stackers, Libraries)

I use the term "robotics" to refer to access to multiple removable 
volumes by a fewer number of drives without a person.  This includes 
sequential stackers, as well as random access robotics.

A stacker typically is capable of taking (literally) a stack of tapes
and putting them into the drive one at a time, in order. No random
access to specific tapes, as with a full-function autochanger.
Stackers typically are limited to 8-10 cartridges, and are used by
people whose backups have exceeded the size of one cartridge.

In the larger media formats, such as D-1, D-2, Betacam, etc., the
traditional manufacturers of broadcast autochangers, such as Asaca,
Odetics, Sony, etc. have products that are easily adaptable to storage
use.

The August 1996 issue of Byte magazine has an article comparing 12
tape autochangers.  It is a little misleading, not mentioning any of
the truly large library systems, and only one midrange, whose capacity 
is quoted assuming DLT 7000 tape drives, which is never mentioned.  In 
addition, much of their testing is more related to the drives than the 
autochangers.