Compaq 4200 Family - Manual (Page 25)

Chapter
3
I/O Module
This chapter discusses the operation and function of the LVD disk enclosure I/O module
(the “module”).
Each enclosure requires an I/O module for operation with a wide (16-bit) controller SCSI
bus. The module is the CRU that connects the enclosure to the host controller through a
68-pin, VHDCI connector and a SCSI bus cable. This module can support a maximum of
14 drives in a single enclosure or on a single-bus.
The host adapter or controller determines whether the external bus is LVD or SE.
Regardless of the host controller type, the internal SCSI bus to the devices is always a
Wide-Ultra2 SCSI LVD bus.
The module is the interface between the host controller (the initiator) the drives and the
EMU. Each enclosure has two SCSI buses. Half of the disks drive bays are on each bus.
The module shown in Figure 3–1 links the two SCSI buses into a single bus.