user manual

AMD Athlon™ Processor Microarchitecture Summary 5
22007E/0—November 1999 AMD Athlon™ Processor x86 Code Optimization
AMD Athlon execution core to achieve and sustain maximum
performance.
As a decoupled decode/execution processor, the AMD Athlon
processor makes use of a proprietary microarchitecture, which
defines the heart of the AMD Athlon processor. With the
inclusion of all these features, the AMD Athlon processor is
capable of decoding, issuing, executing, and retiring multiple
x86 instructions per cycle, resulting in superior scaleable
performance.
The AMD Athlon processor includes both the industry-standard
MMX SIMD integer instructions and the 3DNow! SIMD
floating-point instructions that were first introduced in the
AMD-K6
®
-2 processor. The design of 3DNow! technology was
based on suggestions from leading graphics and independent
software vendors (ISVs). Using SIMD format, the AMD Athlon
processor can generate up to four 32-bit, single-precision
floating-point results per clock cycle.
The 3DNow! execution units allow for high-performance
floating-point vector operations, which can replace x87
instructions and enhance the performance of 3D graphics and
other floating-point-intensive applications. Because the
3DNow! architecture uses the same registers as the MMX
instructions, switching between MMX and 3DNow! has no
penalty.
The AMD Athlon processor designers took another innovative
step by carefully integrating the traditional x87 floating-point,
MMX, and 3DNow! execution units into one operational engine.
With the introduction of the AMD Athlon processor, the
switching overhead between x87, MMX, and 3DNow!
technology is virtually eliminated. The AMD Athlon processor
combined with 3DNow! technology brings a better multimedia
experience to mainstream PC users while maintaining
backwards compatibility with all existing x86 software.
Although the AMD Athlon processor can extract code
parallelism on-the-fly from off-the-shelf, commercially available
x86 software, specific code optimization for the AMD Athlon
processor can result in even higher delivered performance. This
document describes the proprietary microarchitecture in the
AMD Athlon processor and makes recommendations for
optimizing execution of x86 software on the processor.