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AMD’s HyperTransport Bus


HyperTransport is a fast interconnect bus used in AMD chip for connecting the processor to a chip ( called North Bridge).  A typical AMD chip looks very much like the one shown in the block diagram below.

block diagram showing AMD processor with Memory and Chipset.

This is a typical block diagram of almost all the processors launched. It typically has two bus interconnection. It connects to a DDR3 ( or other memory chip ) on one hand and to a chip called North Bridge Chip on the other hand. The connection to the chipset is accomplished using the HyperTransport. A server chip may have more than one HyperTransport Bus. The second ( or third) HyperTransport Bus is used for communication with another processor.
HyperTransport provides a much higher bandwidth than was possible in earlier architectures like FSB Bus. It has a much higher clock speed, made possible by using differential signaling. In Differential signaling two wires are used to transmit information between transmitter and receiver. At the receiver end the difference between the positive and the negative wires is used to determine a high or a low. Since we are only concerned about the “difference” in the voltage rather than the absolute voltage, it is mores immune to noisy environment and is able to achieve higher clock frequency.

HyperTransport works on rising as well as the falling edge of the clock doubling the data speed. The width of the HyperTransport Bus is “Scalable”. To get a maximum throughput you can use all the 32 bit wide bus. But if you do not wish to utilize ( because you not need that much of bandwidth) you can reduce the width to lower width saving the motherboard design and chipset complexity.

A Bidirectional Bus – HyperTransport is a bidirectional Bus. The data can transfer from A to B in concurrence with a Transfer from B to A.

How much Bandwidth – HyperTransport has been scaled up to provide higher bandwidth in the successive revisions. In the table below we present the maximum clock speed and the maximum bandwidth achieved by the Bidirectional Bus.

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