The Athlon Microarchitecture

The Athlon Microarchitecture at a Glance

The K6 series of CPU's were notorious for having a non-pipelined floating point unit. (FPU) Having a strong FPU is critical for processing floating point instructions present in today's advanced 3D games. In first-person shooters such as Quake, the K6 lagged behind similar Intel products. AMD alleviated this problem with its 3DNow! instructions released with the K6-2 and K6-III line of processors, but for applications that didn't take advantage of 3DNow!, performance still suffered. To correct this problem, AMD added three floating point execution units to the Athlon architecture. For reference, today's Pentium III only has two. To top it off, AMD added 128K of L1 cache versus the 32K present in the Pentium III. Both CPU's offer 512K L2 cache running at ½ the speed of the processor. However, Intel's newer Coppermine CPU's feature 256KB L2 cache running at the same speed as the CPU.

Get On The Bus

Another additional feature present in the Athlon CPU is the 200MHz EV6 bus licensed from Digital. Unlike Intel's P6 bus which features a 100MHz frontside bus, the EV6 bus is a point-to-point bus. This means that various components such as RAM and the CPU itself all have their own exclusive "channel" (or path) to the chipset. With the P6 bus, each component shares the 100MHz frontside bus. If you were to add a second CPU to the system, the second CPU gets its own 200 MHz path to the chipset present on the motherboard. With Intel's P6 bus, both CPU's share the 100 MHz frontside bus.

3DNow! Take 2

To top it off, AMD added 24 new SIMD instructions to its 3DNow! instruction set. 19 of these new instructions are designed to enhance MMX math and streaming content on the Internet, while the other 5 are designed to improve the Athlons performance when encoding and decoding MP3's, Dolby Digital, and MPEG2 applications.

So what do all these new performance features add up to? Intel's worst nightmare, a legitimate performance threat to its Pentium III line.

The MHz War

In order to remain a threat, AMD also realized that it couldn't lag behind Intel in the MHz war. For if they fall behind too quickly they may lose the mindshare they've tried so hard to gain. For this reason, the Athlon launched at four speeds, 500, 550, 600, and 650MHz. At the time of their launch in August, the Athlon was the fastest desktop CPU available in terms of real world performance and sheer clock speed.

Following the Athlon announcement in August, AMD noticed that yields on 650 MHz CPU's were quite good, in fact, they noticed they had enough CPU's to release a 700 MHz product. On October 3rd, AMD officially announced the Athlon 700 to the surprise of many analysts. After all, no one was sure if AMD could supply a 650 MHz product en masse; with the 700 MHz release they silenced any doubters.