Athlon 64: Why 64-bit Computing Matters Today

It’s September 2003, and the "Megahertz Myth" is finally dying. While Intel has been struggling to push the Pentium 4 to higher clock speeds with increasingly long pipelines, AMD has taken a different path. Today, they released the Athlon 64, and it’s a masterstroke.

The 4GB Barrier

The biggest reason we need 64-bit is the memory. 32-bit processors can only address 4GB of RAM (2^32). A few years ago, that seemed like an infinite amount, but with modern databases, video editing, and heavy multitasking, we are starting to hit that ceiling. 64-bit computing expands that limit to a staggering 16 exabytes.

AMD64 vs Itanium

What makes the Athlon 64 (AMD64) brilliant is its approach to compatibility. Intel tried to move to 64-bit with the Itanium (IA-64), but it was a completely new architecture that ran 32-bit code painfully slowly through emulation. It was a "clean break" that nobody wanted.

AMD64 is an "evolutionary" approach. It adds 64-bit registers and addressing modes but remains natively compatible with 32-bit x86 code. You can run your old 32-bit OS and apps today, and when 64-bit versions of Windows and Linux are ready, you’ll get a performance boost from the extra registers.

Integrated Memory Controller

The Athlon 64 also moves the memory controller off the motherboard chipset and directly onto the CPU die. This drastically reduces memory latency.

Looking Ahead

AMD has just defined the next decade of x86 computing. Intel will almost certainly have to follow suit and adopt the AMD64 instruction set (they’ll probably call it EM64T or something else to avoid giving AMD credit).

As developers, we need to start thinking about "Long Mode." We’ll have 16 general-purpose registers instead of 8, and SSE instruction sets will be standard. It’s time to start recompiling.