Pci Architecture; Scsi Controller - HP Digital AlphaStation 255 Family User Information

System Overview
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Bays for one or two internal hard drives: two 3.5 by 1-inch hard disk drives or one 3.5
by 1.6-inch hard disk drive and one 3.5 by 1-inch hard disk drive.
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SCSI-2 controller connects directly to the on-board PCI bus and supports up to seven
8-bit, single-ended SCSI devices (such as hard disk drives and CD-ROM drives)
running at up to ten million transfers per second (fast SCSI).
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Four I/O slots (PCI, ISA, and PCI/ISA combination) are distributed as follows: two
PCI, one combination PCI/ISA, and one ISA.
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Keyboard and mouse ports.
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Two serial ports.
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Ethernet twisted-pair connector.
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One enhanced bidirectional parallel port.
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High-performance graphics adapter.
Refer to Appendix B, Technical Specifications, for additional information.

PCI Architecture

Your system's PCI architecture represents the latest advances in local bus technology. The
Digital AlphaStation 255 system's PCI architecture delivers maximum performance by
providing a wider data path, greater speed, and improved expandability. PCI removes
various types of peripheral controllers from the slower ISA bus and connects them directly
to a wider, faster data path. The result is faster data transfers for devices such as SCSI
controllers and high-end video adapters—a critical advantage when you are running
graphic- and I/O-intensive software.
The PCI bridge chip (in the chipset) can be the PCI bus master, generating cycles on the
PCI bus, or it can act as a bridge between the PCI bus and memory. It can generate all
types of PCI cycles and responds to cycles initiated by devices requiring access to
memory. It performs translation of addresses supplied by other PCI devices acting as bus
masters.
The PCI interface clock speed is fixed at 33.33 Mhz, for a 30.0 ns cycle time. The
theoretical maximum instantaneous burst data rate is 132 MB/s.
The PCI includes PCI-to-ISA bridge capability that allows you to use commonly available
ISA options.

SCSI Controller

The Digital AlphaStation 255 system has a fast SCSI-2 controller that controls
up to seven SCSI peripherals such as hard disk drives, CD-ROM (compact disc
read only memory) drives, and tape drives.
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