Digital Equipment RW504-ZA, Service Manual

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uninterruptable power supply (UPS) be used with battery backup to ensure that
no data is lost if a power failure occurs.
1.3.2 Magneto-Optical Disks
Magneto-Optical (MO) disks are more durable, more reliable, removable, and cost
far less per megabyte than magnetic disks. MO disks are made of the same kind
of plastic used in bullet-proof windows. Data can be read through fingerprints
and minor scratches. MO disks can withstand x-rays, magnetic interference, and
can be dropped from desk height without damage.
Magneto-Optical disks store data on a magnetic layer in the form of magnetic
flux reversals rather than on a pitted surface used in other optical technologies.
Because surfaces of the MO disk are not physically changed, they can be written
to and erased repeatedly with no measurable data degradation. Optical disks
have an archival life of thirty years based on accelerated life tests for data
retention.
The disk is mounted in a rigid plastic case with a metal shutter, similar to a
3.5-inch magnetic flexible disk. Optical disk storage capacity varies depending
on the disk type. (Check the host system documentation to determine which disk
format is supported.) The MO disk has two recording sides. To access the second
side, the cartridge must be ejected, turned over, and reinserted into the drive.
There are two types of magneto-optical disks: rewritable optical disks and write-
once optical disks. (Check the host system documentation to determine which
disk type(s) are supported.) The two disk types can be differentiated by the words
‘‘rewritable’’ or ‘‘write-once’’ printed on the disk’s metal shutter.
For data safety, you can independently write-protect each side of the disk by
setting the write-protect tab on the corner of the cartridge.
1.4 SCSI Interface Options
The optical disk library connects to the host system with a single-ended SCSI
interface This interface conforms to SCSI standards ANSI X3.131-SCSI-2.
1.4.1 Single-ended SCSI Interface
The single-ended interface specifies the use of a single-ended SCSI repeater PCA.
This PCA enables the library to be connected to an external single-ended SCSI
bus. The total SCSI cable length between peripherals and the host is 6 meters.
In addition, an internal SCSI cable length of 2.1 meters must be included in this
calculation.
Introduction 1–5