Owner`s manual

Page 1-6 Chapter One
AM-6000 Computer Owner's Manual, Rev. 02
• Selection of any hard disk ID number as the primary boot disk (unit #0 - 6). In the case of the
Wide SCSI interface coupled with Wide SCSI peripherals, you can also select unit #8 - 15*.
• Selection of any tape device as an alternate boot device (unit #1 - 6). In the case of the Wide
SCSI interface coupled with Wide SCSI peripherals, you can also select unit #8 - 15*.
• Operator entry to boot the system with any valid monitor and/or initialization file name, located
in [1,4] of the first logical of the selected boot device
• Selection between the AM-319-20 AUI or TPI port for Ethernet connection
* SCSI ID 7 is reserved for the host.
SCSI and Wide SCSI Disk Drives
The SCSI controller in the AM-6000 provides two bus interfaces, each originating at a connector on the
AM-176 board. One is a 50-pin SCSI bus interface, the second is a 68-pin Wide SCSI bus interface. Both
interfaces support Alpha Microsystems SCSI disks, streamer tapes, DAT tapes, CD-ROMs and the AM-
642 SCSI to Pertec Converter for ½" tape drives. However, you cannot attach peripherals to both busses
in the same computer!
For peripheral compatibility and system performance, the significance of the two busses is as follows:
• The "narrow" SCSI bus is one byte wide (8 bits plus parity) and supports a maximum transfer
rate of 10MB per second.
• The Wide SCSI bus is twice as wide: two bytes, or 16 bits plus 2 parity bits. Doubling the width
of the data path doubles the maximum transfer rate to 20MB per second.
The Wide SCSI bus has the following advantages:
• Disk-intensive applications are potentially faster with Wide SCSI disk drives.
• It supports up to 15 devices, where standard SCSI supports only seven, so you can potentially
work with bigger configurations.
These busses are mutually exclusive. That is, all devices must connect to one of the two busses; the other
connector cannot be used. Although not recommended, using the appropriate adapters, you can connect a
mix of SCSI-2 drives and Fast-Wide SCSI-2 disk drives to either SCSI bus.
For optimum performance, use Wide SCSI-2 drives attached to the Wide (68-pin) SCSI
connector. Mixing SCSI-1, SCSI-2, and Wide SCSI-2 disks on the same bus tends to degrade
performance and is not recommended.
External SCSI Port
Your computer includes an external SCSI (Small Computer Standard Interface) port to which you can
attach additional SCSI compatible storage devices. Such as hard disk drives, a CD-ROM drive, or
magnetic tape storage devices. Whether or not you are using an external SCSI device, make sure the
SCSI cable is terminated properly. This normally means plugging an external active terminator into the
external SCSI port.