Editing 5ESS Switching System (section)

===Administrative Module===
The Administrative Module (AM) is a dual-processor mini [[main frame computer]] of the AT&T [[3B series computers|3B series]], running [[UNIX-RTR]].  AM contains the hard drives and tape drives used to load and backup the central and peripheral processor software and translations.  Disk drives were originally several 300 megabyte [[Storage Module Device|SMD]] multi-platter units in a separate frame. Now they consist of several redundant multi-gigabyte [[SCSI]] drives that each reside on a card.  [[Magnetic tape data storage|Tape drives]] were originally half inch open reel at 6250 [[bit]]s per inch, which were replaced in the early 1990s with 4&nbsp;mm [[Digital Audio Tape]] cassettes.

The Administrative Module is built on the [[3B21D]] platform and is used to load software to the many [[microprocessors]] throughout the switch and to provide high speed control functions.  It provides messaging and interface to control terminals.  The AM of a 5ESS consists of the 3B20x or 3B21D processor unit, including I/O, disks, and tape drive units.  Once the 3B21D has loaded the software into the 5ESS and the switch is activated, [[packet switching]] takes place without further action by the 3B21D, except for billing functions requiring records to be transferred to disk for storage.  Because the processor has duplex hardware, one active side, and one standby side, a failure of one side of the processor will not necessarily result in a loss of switching.