HyperTransport System Limits
HyperTransport shares PCI terminology in describing a system in terms of the number of buses, devices, functions, and configuration space.
256 Buses In A System
PCI permits 256 buses in a system and each PCI host bridge or PCI-to-PCI bridge secondary interface is host to a new bus with a unique bus number. Unlike PCI, a HyperTransport bus may not end with a single electrical connection. Tunnel devices enable the construction of device chains which are still viewed as a single logical bus. The 256 bus limit in HyperTransport, then, is actually 256 chains.
32 UnitIDs Per Bus
PCI permits a maximum of 32 physical devices per bus. In HyperTransport, each functional device can request multiple device numbers, called UnitIDs. ...
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