Ok, I went through a few papers and this is what I got:
- Until AGP "8x" the spec only allows one device to be seen on the AGP slot
- Not a big deal when it comes to V5 5500 since two VSA100 can be connected to each other directly and only the master is shown to the AGP/PCI interface
- More than two VSA100 require a bus system, because there are dedicated communication interfaces that can't be connected to each other directly => AGP can't do the job (only one device allowed) so PCI is the bus system to go. In order to show the AGP interface only one device, the bridge is used to fulfill this requirement