T
ECHNOLOGY
B
RIEF
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Implementing 64-bit, 66-MHz PCI technology increases bandwidth to a theoretical 532 MB per
second, double the bandwidth of 33-MHz implementations. Although 3.3-volt, 33-MHz cards
may be plugged into the 66-MHz slots, no performance benefit will be achieved. In fact, doing so
will slow down the PCI bus such that all slots on the same bus will operate at 33 MHz, potentially
reducing the performance of any 66-MHz device in another slot on that bus.
As long as the proper 64-bit drivers have been installed to interface with the Itanium system, 32-bit
PCI cards may be plugged into the 64-bit PCI slots. However, the 66-MHz slots have been keyed
so that 5-volt PCI cards cannot be inserted. This eliminates the potential to damage the cards by
inserting them into the wrong slots.
System Board Design
The Itanium processor and its power module (Figure 5) are much larger than the 32-bit Pentium III
Xeon processor and its power module. They are also much heavier. Compaq engineers worked
closely with Intel to drive innovations in the processor board design so form factor, modularity,
and serviceability would not be sacrificed to accommodate the larger footprint and weight.
Figure 5: The Itanium processor and power module are much larger than the 32-bit Pentium
Xeon processor and its power module.
For example, Compaq required the use of very high-density metric connectors to provide tool-free
insertion and removal of the processor and memory drawer in the ProLiant DL590/64 server.
Compaq also required that these connectors be placed on one side of the board. This enhances
cooling by allowing the processor board to plug into a side plane instead of a midplane, which
would restrict front-to-back airflow.
A dual-sided design allows the processor board to accommodate the four Itanium processors,
associated power modules, and a maximum of 64 GB of memory in a mirror-image configuration.
Of course, the more powerful processor and greater memory capacity place enormous power
requirements on the server.
To handle these power requirements, Compaq designed the I/O board (Figure 6) and the side plane
with an innovative bus bar technology. The bus bar accommodates the high current and high-
speed buses that are routed through the board while keeping the layer count and cost of the board
down.
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TC020702TB
