Athlon 64 for Quiet Power

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June 15, 2004 by Bryan Cassell

A detailed discussion of the AMD Athlon 64 Processor as it pertains to silent computing by Bryan Cassell, with rejoinders by Russ Kinder and yours truly. Bryan is a new contributor to SPCR who is no beginner to computing or PC silencing, and works as a software programmer. Enjoy!

— Mike Chin, Editor of SPCR

This article deals with the Athlon 64—probably the most talked about, yet least understood processor of the current generation. I’ll deal with the facts and myths surrounding the Athlon 64, and share some of my personal experiences with this exceptional CPU.

So what makes the Athlon 64 special? How is it different from any other x86 CPU?

The A64's copper heat spreader is a relief for those concerned about core damage (oft seen with the original Athlon and Athlon XP CPUs).

Architecturally, there are two main differences that set the Athlon 64 apart from its predecessors and its competition:

Integrated Memory Controller

The first major difference is the memory controller. For as long as x86 PC’s have existed, the memory controller (the logic chip that actually communicates with your RAM) has been located on the motherboard, usually as a part of the chip that we now call the northbridge. In this configuration, when the CPU wants to access a piece of memory, it sends the memory read commands over a high-speed connection (known as the front side bus) to the memory controller. The memory controller then interprets those commands, fetches the data from your RAM, and sends the data back across the front side bus to your CPU.

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The Athlon 64 has completely bypassed this mechanism and placed the memory controller directly on the CPU. The CPU itself has a direct, high-speed connection to the RAM. When the Athlon 64 wants to access a piece of memory, it simply fetches the data itself directly from memory. Because of this direct path, the latency from when the data is requested to the time that it is received is significantly reduced.

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64-bit Extensions

The other, and most touted, difference with the Athlon 64 is the fact that it is a 64-bit processor (hence the name Athlon 64). What it actually means to be a “64-bit processor” is a subject of much debate, but in the case of the Athlon 64 it simply refers to the x86-64 extensions that the CPU possesses. These extensions provide, among other things, a set of sixteen 64-bit general purpose registers (rather than the eight 32-bit GPRs in the x86 instruction set), as well as a set of instructions to manipulate data in 64-bit chunks and address memory using 64-bit pointers. If you have no idea what I just said, don’t worry about it, just understand this:

The 64-bit capabilities of the Athlon 64 are merely extensions to the existing x86 instruction set. The Athlon 64 supports, 100% natively, all existing x86 code. The addition of x86-64 extensions is the same thing as the addition of MMX or SSE—it is simply a new feature that will probably provide some performance benefits as soon as software is written to take advantage of it.

Many people have asked me something along the lines of, “Why buy a 64-bit CPU if there is no 64-bit version of Windows out yet?” Well, when Intel released the first SSE capable CPU did you also say “Why buy an SSE capable CPU if there is no software that supports SSE yet?” I would certainly hope not. In time the 64-bit extensions may turn out to provide great benefits (in much the same way that SSE has), but until then the Athlon 64 should be judged for what it is: A great 32-bit CPU which happens to have 64-bit extensions.

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