DEC 4000 600 series, Руководство пользователя, Страница: 181 / 242

CPU Subsystem
Memory Module Main memory provides the electrical storage area for data and
instructions used by the CPU. DEC 4000 AXP systems support
from one to four memory modules.
Each memory module features the following:
• Error detection and correction (EDC) logic
• Memory interleaving across 2 or 4 modules of like sizes
• Read prefetch buffers
• Write transaction buffers
• Block exchange
• Read data wrapping
• Intelligent refresh control
I/O Module Each system has an I/O (input/output) module that allows the
system to access mass storage, backup, and network resources.
The I/O module contains the following:
• Four SCSI-2/DSSI buses for fixed-media devices.
• One SCSI-2 bus for removable-media devices.
• One or two Ethernet ports, based on the third-generation
Ethernet chip (TGEC).
Each Ethernet port has two associated ports: thickwire
(standard Ethernet) and ThinWire. You select either
thickwire or ThinWire with a switch that is located halfway
between the thickwire and the ThinWire ports. You can
connect to a twisted-pair Ethernet by connecting a twisted-
pair H3350 media access unit to the thickwire port, using a
standard transceiver cable.
• Fu Profile B interface (allows both 32- and 64-bit
data transfers).
• Console and diagnostic firmware (512-KB of flash-erasable
read only memory—FEPROM).
• 8-KB of EEROM for console use.
• Time-of-year (TOY) clock, based on Dallas Semiconductor
DS1287.
Learning More About Your System 7–7