HyperTransport comes in four speed versions — 1.x, 2.0, 3.0, and 3.1 — which run from 200 MHz to 3.2 GHz. It is also a DDR or "Double Data Rate" connection, meaning it sends data on both the rising and falling edges of the clock signal. This allows for a maximum data rate of 6400 MT/s when running at 3.2 GHz. The operating frequency is auto-negotiated.
HyperTransport supports an auto-negotiated bit width, ranging from two- to 32-link interconnects. The full-width, full-speed, 32-bit interconnect has a transfer rate of 25.6 GB/s (3.2 GHz/link * 2 bits/Hz * 32 links * 1 Byte / 8 bits) per direction, or 51.2 GB/s aggregated bandwidth per link, making it faster than any existing bus standard for PC workstations and servers (such as Intel sponsored PCI Express) as well as making it faster than most bus standards for high-performance computing and networking. Links of various widths can be mixed together in a single system (for example, one 16-link interconnect to another CPU and one 8-link interconnect to a peripheral device), which allows for a wider interconnect between CPUs, and a lower-speed interconnect to peripherals as appropriate. It also supports link splitting, where a single 16-link interconnect can be divided into two 8-link interconnects. The technology also typically has lower latency than other solutions due to its lower overhead.
The primary use for HyperTransport is to replace the front-side bus, which is currently different for every type of machine. For instance, a Pentium cannot be plugged into a PCI Express bus. In order to expand the system, the proprietary front-side bus must connect through adapters for the various standard buses, like AGP or PCI Express. These are typically included in the respective controller functions, namely the northbridge
In contrast, HyperTransport is an open specification, published by a multi-company consortium. A single HyperTransport adapter chip will work with a wide spectrum of HyperTransport enabled microprocessors. For example, Broadcom HT-1000 and HT-2000 server controller devices can work with many different HyperTransport enabled microprocessors.
AMD uses HyperTransport to replace the Front-Side Bus in their Opteron, Athlon 64, Sempron 64, Turion 64, and Phenom families of microprocessors.
HyperTransport - Wikipedia, the free encyclopedia