PCI Alignment in the 9600

Just an old instruction I found on PCI-slot order and potential issues/resolutions. Interesting read and good to know in advance:

In Power Macintosh 9500 and 9600 systems (including the Power Macintosh 9600/200MP), there are six PCI slots (A1, B1, C1, D2, E2, F2), which are serviced by two PCI controller chips (Bandit 1 and Bandit 2). Theoretically, each controller chip can handle up to four PCI cards. However, in order to even the data bandwidth load, three PCI slots are distributed to each controller. Specifically, Bandit 1 controls slots A1-C1, and Bandit 2 controls slots D2-F2. This distribution can almost be thought of as two PCI buses with three slots each.

The slots on the logic board are labeled by letter and number. The labelling, which is printed next to the slot, is used only to identify the physical location of the slot on the logic board. Located between the Power Supply and the bottom of the case, the slots look like:

Power Supply

————— PCI Slot A1
————— PCI Slot B1
————— PCI Slot C1
————— PCI Slot D2
————— PCI Slot E2
————— PCI Slot F2
Bottom of Case

Additionally, the I/O circuitry on the logic board, which controls functions such as ADB and Serial I/O, was designed to be accessed through the PCI bus. The I/O circuitry functions as a PCI card built into the logic board. When considering performance of the PCI bus, it can be assumed that I/O functions will consume some of the bandwidth of the PCI bus. Depending on the amount of I/O activity, the PCI bus handling I/O may run slower than the PCI bus that does not.

On Power Macintosh 9500 and 9600 systems, the I/O functions are handled by the first PCI controller (Bandit 1). Because the first PCI controller handles both I/O functionality and slots A1-C1, performance of cards in these slots may be decreased.

In order to achieve optimal performance of PCI cards, slots D2-F2 should be used first. However, when using high-bandwidth cards, which are moving large amounts of data across the PCI bus, it may be beneficial to evenly distribute the cards between the two buses. In such circumstances, it is likely that the I/O bandwidth is much smaller than that of the high-bandwidth card. To distribute data evenly across the entire PCI bus, you may want to use the following order: D2, A1, E2, B1, and so on.

This article was published in the Information Alley on 02 July 1996.

Via: Frank Sottile on xlr8yourmac


Update:  RacerX reacted and informed me that the bottom 3 PCI-slots are performing better than the top 3 ones – something usefull to be considered when installing video cards. And furthermore: ‘Apple’s strategy for PCI card placement in both the 9500 and 9600 series was to put the card that needed the most bandwidth in the bottom three slots followed by the card that required the second most bandwidth in the upper slots.’

Thanx for the info.


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