AMD Unveils New Bus Architecture

ENT, March 26, 2001 by CHRISTOPHER McCONNELL

Advanced Micro Devices (AMD) turned heads with its high-performance Athlon processor, but it made little inroads into the enterprise since it did not support multiprocessing. The company's new HyperTransport bus architecture will offer multiprocessing and improved I/0 performance.

AMD hopes to replace the PCI bus with the new HyperTransport bus, which offers chip-to-chip connectivity and high-speed connection to I/0 devices. The first third-party HyperTransport products will hit the market later this year.

The Hyper Transport bus consists of a 6.4 GBps connection for devices inside a machine. A Control Logic (CL) chip sits outside each device, packeting data and sending it out on the wire. Devices at the receiving end also have a CL for decoding the packets. With multiplexing, HyperTransport will be able achieve speeds in multiples of 6.4 GBps.

"HyperTransport is a big part of our future plans," says Charles Mitchell, product strategy manager at AMD. Mitchell believes HyperTransport will boost performance on high-end workstations and deliver multi processing capabilities to AMD based servers.

Some reports have compared HyperTransport to Intel's up coming InfiniBand architecture, but the two initiatives will not compete with one another, at least in early implementations. InfiniBand will first be deployed as a means to connect independent devices, HyperTransport will provide connectivity inside a machine.

AMD's first HyperTransport products for multiprocessing will likely coincide with the release of the 64-bit "Hammer" processor in the first half of next year. AMD will focus on Hammer for its entry into the multiprocessor server space.

The Hammer processor will mark AMD's entry into enterprise-class servers. HyperTransport offers chip-to-chip connectivity that enables greater than two-way multiprocessing, unavailable with AMD's current products.

Processors are connected to a CL that processes I/O between the processor, memory bank, and the rest of the system. Two chips can share a CL and a memory bank, and CLs can be connected to one another for greater degrees of multiprocessing. CLs can access the memory of another CL, distributing instructions across multiple processors. "This is a variant on the NUMA [Non-Uniform Memory Access] architecture," Mitchell says.

Nathan Brookwood, analyst at Insight64 Group, says other vendors may release multiprocessing solutions based on HyperTransport before AMD. He points to API Networks, a company experienced with multiprocessor Alpha machines, as a likely candidate.

HyperTransport will also offer a new way to connect I/O devices such as graphics and network cards. HyperTransport can connect graphics controllers directly to processor and memory at the CL, while devices such as network cards can connect to HyperTransport natively or another CL can connect to a standard PCI or PCI-X bus.

Mitchell says connecting I/O devices to HyperTransport will improve performance for all machines, since computers have begun to hit the limitations of the PCI bus. "You need to do something to open up the bandwidth for these devices," he explains.

Brookwood says graphics chip vendors will be some of the first to take advantage of the HyperTransport architecture. Graphics chip vendors ATI Technologies Inc. and nVidia Corp. publicly announced their support for HyperTransport.

Networking vendors may be slower to adopt HyperTransport, Brookwood says. Cisco Systems and Mellanox Technologies, for instance, have said that they plan to support HyperTransport, but Mitchell expects Cisco to use HyperTransport as an internal architecture for switches, while Mellanox is primarily an InfiniBand vendor. For traditional IP network hardware, native HyperTransport may be a hard sell. "I don't expect you'll talk the 3Coms of the world into tying that directly into HyperTransport," Brookwood says.

Hyper Transport will not be the first to offer multiprocessing capabilities on AMD-based machines. Both Mitchell and Brookwood say a dual Athlon chipset will arrive in a few months. Brookwood believes the chipset will be based around AMD's 760 chipset, which only supports a single processor today.

These chipsets will only support two processors, but Brookwood says they will He says dual-Athlon machines will enable AMD to gain credibility in the server space before the Hammer release. "Those are markets AMD has not been traditionally associated with," he says.