Advanced Micro Devices recently reintroduced its Lightning Data Transport (LDT) under a new name, HyperTransport, and disclosed a broad set of backers among PC chip companies and networking concerns. AMD claims that more than 100 companies are working on HyperTransport products, giving the interface momentum toward becoming a widely used standard.
HyperTransport began as a way to link the north and south bridge in a PC chip set, boosting bandwidth beyond what PCI offers. AMD needed a solution because Intel had picked a proprietary hub bus.
HyperTransport uses unidirectional 400-MHz serial links. With eight data links in each direction and just 55 pins, it can deliver up to 1.6 Gbytes/second, six times the bandwidth of standard PCI.
By adjusting the number of data links from two to 32, vendors can tailor the bandwidth to their needs while maintaining a low pin count. Acer Labs, ATI Technologies, Nvidia, Silicon Integrated Systems and Via Technologies-all the major PC chip-set makers except Intel-plan to deploy HyperTransport chip sets.
PCI is also widely used as a backplane in networking, and with network bandwidth rising rapidly, the bus is running out of gas there too. HyperTransport offers networking vendors a standard way to connect chips without straining tight pin counts.
SiByte (now part of Broadcom) became the first vendor to announce a HyperTransport product: its SB-1250 dual-core MIPS processor. With PMC-Sierra (owners of QED) and Sandcraft supporting HyperTransport, the interface is likely to become the standard for connecting control-plane processors with data-plane chips.
Competition comes from RapidIO (www.rapidio.org), which also has a large number of backers. Except for founder Motorola, however, most RapidIO supporters are OEMs, not chip companies.
HyperTransport's momentum comes in part from its low licensing fees. And unlike Motorola, AMD is not a direct competitor to vendors of control-plane processors and network processors, making it a more palatable technology partner for some companies (save Intel, of course).
Network processor vendors are seeking a faster, low-pin-count replacement for PCI. Most have stayed on the fence between HyperTransport and RapidIO. By the end 2001, look for several network processor vendors to endorse AMD's technology.
Linley Gwennap, Co-author of "A Guide to Network Processors" (www.linleygroup.com/npu), is principal analyst of the linley group.
