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IBM
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xSeries 450 Planning and Installation Guide
If there is a mismatch between the total memory in port 1 and the total memory in
port 2, then there will be a delay when accessing the upper memory. For example
if you have two 512 MB DIMMs and two 1 GB DIMMs, memory accesses to the
first 2 GB of memory (1 GB from each port) will be at maximum rate of 6.4 GBps.
However, the remaining 1 GB (the upper half of the 1 GB DIMMs) will only be at
3.2 GBps maximum.
3.1.3 PCI slot configuration
As shown in Figure 1-1 on page 4, there are six PCI-X slots internal to the x450.
These six slots are implemented using four PCI buses:
Bus A (slot 1 and slot 2): Two 64-bit 66 MHz slots
Bus B (slot 3 and slot 4): Two 64-bit 100 MHz slots (133 MHz if only one slot is
occupied)
Bus C (slot 5): One 64-bit 133 MHz slot
Bus D (slot 6): One 64-bit 133 MHz slot
These slots can accept adapters rated at speeds ranging from 33 MHz to 133
MHz.
You should also consider the following:
Each adapter has a maximum rated speed. Each bus also has a maximum
rated speed.
Installed adapters in a single bus will operate at the slowest of three speeds:
– The rated speed of adapter 1
– The rated speed of adapter 2 (if the bus the adapter is installed in has two
slots)
– The rated speed of the bus
Bus B supports one adapter at up to 133 MHz or two adapters at up to 100
MHz.
32-bit adapters can be installed in any of the slots and will run in 32-bit mode.
32-bit and 64-bit adapters can coexist in 64-bit slots in the same bus. The
32-bit adapters will run in 32-bit mode, and the 64-bit adapters will run in
64-bit mode.
Tip:
Take the time to understand these rules and to select the best slots for
your adapters. Incorrect choices can result in a loss of PCI adapter
performance.
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