IBM 88554RU Installation Guide - Page 75

3.1.3 PCI-X slot configuration As shown in Figure 1-4 on page 8, there are six PCI-X slots internal to the x455. These six slots are implemented using four PCI buses: Bus A (slot 1 and slot 2): Supporting two 64-bit adapters at up to 66 MHz Bus B (slot 3 and slot 4): Supporting two 64-bit adapters at up to 100 MHz, or one adapter at up to 133 MHz, provided the other slot is vacant Bus C (slot 5): Supporting one 64-bit adapter at up to 133 MHz Bus D (slot 6): Supporting one 64-bit adapter at up to 133 MHz 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 maximum 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. As extreme configuration examples, you could configure either of the following: Six 33 MHz PCI adapters, all operating at 33 MHz Six 133 MHz PCI-X adapters, with two operating at 133 MHz (buses C and D), two at 100 MHz (bus B), and two at 66 MHz (bus A) Chapter 3. Planning 61