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Chapter 2. Positioning 47
on that port would send the alert and take down the DIMM, but keep the system
running out of the redundant memory bank.
To maintain throughput to the processors, the x440 memory subsystem improves
performance by the use of four-way interleaving. Interleaving improves memory
performance because multiple 64-bit objects can be transferred into the memory
controller in a single operation. This improves the memory performance by
reducing the latency time.
For more information regarding an x440 memory subsystem, refer to 1.7,
“System memory” on page 19.
2.2.5 Active PCI-X
PCI-X is a new PCI bus specification and is now available on the xSeries 440. It
was developed to satisfy the increased requirements of I/O adapters such as
Gigabit Ethernet, Fibre Channel and Ultra 3 SCSI. PCI-X is fully compatible with
standard PCI devices.
PCI-X provides a new generation of capabilities for the PCI bus, including more
efficient data transfers, more adapters per bus segment, and faster bus speeds
for server systems. PCI-X enhances the PCI standard by doubling the throughput
capability and providing new adapter-performance options while maintaining
compatibility with PCI adapters.
PCI-X allows all current 66 MHz PCI adapters, either 32-bit or 64-bit, to operate
normally on the PCI-X bus. PCI-X adapters take advantage of the new 100 MHz
and 133 MHz bus speeds, which allow a single 64-bit adapter to move as much
as 1 GB of data per second.
Additionally, PCI-X supports twice as many 66 MHz/64-bit adapters in a single
bus as PCI. Active PCI-X also increases total server availability by letting you add
or replace Active PCI and Active PCI-X cards without having to shut down your
xSeries servers.
2.2.6 XpandOnDemand scalability
XpandOnDemand scalability represents an industry-standard implementation of
true “pay as you grow” scalability. New levels of scalability are achieved with the
Enterprise X-Architecture platform using enhanced, high-performance SMP
building blocks that allow effective scalability beyond four-way SMP.