AMD demos ClawHammer

The console gaming world has often used the bit-width of a processor's data paths to separate generations of hardware, and successive 32-bit, 64-bit, and even 128-bit consoles have quite obviously been faster and more powerful. But at their core, most of these processors have still only had 32-bit registers for integer math and memory addressing. The transition to a 64-bit core is complex one, and often requires vast changes to how software is written, breaking compatibility with existing software. Intel's 64-bit Itanium, a processor intended for high-end servers, is one such example, since it has to emulate support for 32-bit applications. But PC processors are now also making that transition. AMD has taken a very different approach with its next generation of CPUs for desktops and servers, which natively support both 32-bit and 64-bit processing.

AMD's next generation comes in two forms: a desktop CPU called "ClawHammer" and a server CPU called "SledgeHammer." AMD publicly demonstrated ClawHammer this week at a location near the Intel Developer Forum. The two designs are fundamentally similar, but SledgeHammer will have a larger memory cache on the chip, extra reliability features, and a different socket interface. Both ClawHammer and SledgeHammer will run either a standard 32-bit operating system or a 64-bit operating system. AMD's demonstration used the 32-bit version of Windows XP and a 64-bit version of Linux (the 64-bit version of Windows XP hasn't been released and its current preview releases are specifically for the Intel Itanium). The big advantage of having a 64-bit operating system is that it lets a system have much more than 4GB of memory--the current limit. The first demonstration chips are extremely early and aren't running at AMD's target speed (we've previously reported that AMD is targeting 2GHz at release), but it's a very good sign that there are working chips at this early date. Both ClawHammer and SledgeHammer will launch late this year.

The 64-bit support isn't the only significant difference between AMD's popular Athlon chips and ClawHammer. The new chips mark a radical change in PC architecture, integrating control of system memory from its traditional place in the chipset directly into the processor itself. This means that the processors will require a new type of motherboard design, since the processor has extra pins (a total of 754) on its socket interface that talk to the memory. One major reason to move the memory controller into the processor is so that the controller runs at the same speed as the CPU, which can reduce latency.

The other motivation for the integrated memory controllers is for multiple-processor workstation and server designs, where each processor will control its own bank of memory. AMD's high-bandwidth HyperTransport technology (also used by Nvidia in its nForce chipset) connects the processors together with an impressive 6.4GB per second of bandwidth so that they can share data. (Each PC2100 memory channel has 2.1GB per second of theoretical bandwidth so there's not likely to be a bottleneck.) SledgeHammer is designed to work with up to eight processors on a single server motherboard.

While ClawHammer sounds like an extremely complex chip, it's not much bigger than the Athlon XP. The core that was demonstrated covers an area of 100 square millimeters versus 80 square millimeters for the upcoming revision of the Athlon XP, Thoroughbred. Like it did with Thoroughbred, AMD will use a dense .13-micron manufacturing process for ClawHammer. But ClawHammer will also use the even more efficient SOI (silicon on insulator) process to reduce power usage. The Athlon Thoroughbred revision is expected in the first half of this year, while later in the year, AMD will revise the Athlon to also use SOI. This revision is code-named Barton and is the last K7-family Athlon to appear on AMD roadmaps.