HyperTranport Bus was pioneered by Advanced Micro Devices (AMD). The HyperTransport bus is used to interconnect processor to chipset and processor to processor.
The high frequency of the HyperTransport Bus is made possible by the use of the differential signaling. A differential signal requires a set of two wires. In differential signaling, a positive signal is sent on one of the two wires and a negative signal is sent on the other wire. At the receiver side a differential amplifier looks at the difference in the signal to determine if it is a 1 or 0.
HyperTransport Bus was introduced in April 2001 and at the time of writing it comes in 4 versions 1.x, 2.0, 3.0, and 3.1. The latest HyperTransport version 3.1 runs at a clock frequency of 3.2 GHz.
The HyperTransport Bus work at the rising as well as the falling edge of the clock. The HyperTransport 3.1, for example, which has a clock frequency of 3.2 GHz can trasfer 6.4 Million bits ( 3.2 GHz x 2) working as the data is moved on the rising as well as the falling edge of the clock.
The maximum width of the HyperTransport Bus is 32 bit. However designs with 16 bit wide are more common. HyperTransport is a bidirectional bus. The bandwidth of the Hypertransport bus is massive. To give you an idea consider HyperTransport 3.1 bus with 32 bit width working at 3.2 GHz. Since it works on rising as well as falling edge of clock it transfers 6.4 Giga bits per seconds.
The bandwidth is given by 6.4 Giga bits/sec x 32 bits = 204.8 Giga Bits per seconds or 25.6 Giga Bytes per seocond. You can transfer entire content of a 256 Giga Byte Hard disk in just 10 seconds !!! And yes HyperTransport is a bidirectional bus, and both directions and transfer bits simultaneously.
The HyperTransport bus is faster than most other differential bus technologies, including Intel sponsored PCI Express Bus.
HyperTransport Bus is an open specification. It is managed by HyperTransport Consortium. HyperTransport bus replaced the slower front side bus in the AMD processors starting with Opteron Server processor and Athlon 64 desktop processor.