Intel QuickPath Interconnect (QPI) Bus Examined

“So compared to the front side bus QuickPath Interconnect transmits fewer bits per clock cycle but works at a far higher clock rate. Currently the fastest front side bus available on Intel processors is of 1,600 MHz (actually 400 MHz transferring four data per clock cycle, so QuickPath Interconnect works with a base clock eight times higher), meaning a maximum theoretical transfer rate of 12.8 GB/s, the same as QuickPath. QPI, however, offers 12.8 GB/s on each direction, while a 1,600 MHz front side bus provides this bandwidth for both read and write operations – and both cannot be executed at the same time on the FSB, limitation not present on QPI. Also since the front side bus transfers both memory and I/O requests, there are always more data being transferred on this bus compared to QPI, which carries only I/O requests. So QPI will work “less busy” and thus having more bandwidth available.”