Dell Precision 420 User Manual
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Using the Integrated SCSI Controllers: Dell Precision™ WorkStation 420 Systems
User's Guide
Overview
This section provides instructions for installing drivers for the integrated dual-channel Adaptec 7899 Ultra160/m low-voltage differential (LVD)
small computer system interface (SCSI) controller. This controller provides transfer rates of up to 160 megabytes per second (MB/sec) with LVD
hard-disk drives on the primary channel, and up to 40 MB/sec with non-LVD hard-disk drives on the secondary channel. The primary channel also
supports Ultra2 and Ultra SCSI. The desktop chassis supports up to two hard-disk drives, and the mini tower chassis supports up to four hard-disk
drives.
SCSI Device Considerations
The 5.25-inch externally accessible drive bays at the front of the computer are used for non-hard-disk drive devices such as CD-ROM drives
and/or tape drives. These can be enhanced integrated drive electronics (EIDE) or SCSI devices.
NOTICE: Your hard-disk drive subsystem must consist of either SCSI hard-disk drives or EIDE hard-disk drives. Dell does not
support a mix of both types of hard-disk drives.
The desktop chassis has two internal drive bays (located in the drive cage next to the externally accessible drive bays; see Figure 1) that can
accommodate either two SCSI hard-disk drives or two EIDE hard-disk drives. Internal hard-disk drives are mounted vertically in a removable drive
bracket that can contain two 1.6-inch hard-disk drives.
Figure 1. Internal Drive Bays (Desktop Chassis)
The mini tower chassis has four internal drive bays (located in the drive cage beneath the externally accessible drive bays; see Figure 2) that can
accommodate either two EIDE hard-disk drives or four SCSI hard-disk drives. Internal hard-disk drives are mounted vertically in a removable drive
bracket that can contain four 1-inch hard-disk drives, two 1-inch and two 1.6-inch hard-disk drives, or three 1.6-inch hard-disk drives.
NOTES: To achieve 160-MB/sec data transfer rates on the primary SCSI channel, you must use LVD hard-disk drives and either an
LVD terminator or a multimode terminator.
If you install a mix of LVD and non-LVD hard-disk drives, the system can only achieve 40-MB/sec data transfer rates for all SCSI drives.
In addition, the LVD drives in this mix must be capable of reverting to 40 MB/sec. In this configuration, you can terminate the SCSI
subsystem with either a single-ended or multimode terminator.
Dell ships multimode terminators only, regardless of system configuration.
The maximum total length of the SCSI cable for the primary SCSI channel is 12 meters (m). The maximum total length of the SCSI
cable for the secondary SCSI channel is 0.5 m with eight devices or 1 m with four devices.
The total number of SCSI devices connected to the secondary 7899 controller, both internally and externally, cannot exceed 15.
NOTE: Dell supports only the drives it furnishes.
1 Two-bay hard-disk drive cage
(internal)