Performance

Q. Does AMD use Megahertz to compare the K6 against Intel Pentium MMX and Pentium II processors?

A. Yes, the AMD K6 uses a MHz rating. Unlike Cyrix/IBM and their nasty Performance Rating (PR), there a single clear scale for comparison. Raw MHz numbers describe AMD K6 comparison positioning to Intel adequately.

Q. Can I overclock the AMD K6?

A. Yes, the AMD K6 is a good candidate for successful overclocking with a clock multiplier increase, higher bus speed, or both. However, AMD does not support the bus frequency overclocking of its parts. The AMD K6 specification is for a 66MHz bus. AMD voids all warranty and technical support at any other bus setting.

The AMD K6/166 and AMD K6/200 are much more likely to be successfully overclocked than the K6/233. The K6/233 is hindered by its high core voltage and the tremendous amount of heat that it produces. Proper cooling is key in all cases.

The most popular K6 overclocking configuration is the K6/200 (66MHz x 3) running as a K6/225 (75MHz x 3). A K6/233 overclocked to K6/262 or K6/266 is rare. A K6/249 (83MHz x 3) is much more achievable

Intel parts are still the parts of choice for diehard overclockers. It is amazing how far they can be pushed. Accept no substitute if overclocking is your goal. Unfortunately, Intel is aware of rampant overclocking of their parts and is now taking steps to prevent this from occurring.

I have had the least amount of success overclocking Cyrix/IBM parts. Cyrix/IBM seem to rate their parts at the edge of their specifications.

Q. What are the fastest bus speed and clock multiplier combinations for the AMD K6?

A. The table below ranks possible K6 bus speed and clock multiplier combinations according to their performance on the Winstone 97 benchmark. This table will help you squeeze the most performance out of your K6 processor. Hopefully everyone has taken my advice and is using a mainboard that has a 75MHz and 83MHz bus speed.

  1. K6 250/83 (83Mhz x 3.5)
  2. K6 263/75 (75Mhz x 3.5)
  3. K6 266/66 (66MHz x 4)
  4. K6 208/83 (83Mhz x 2.5)
  5. K6 225/75 (75Mhz x 3)
  6. K6 233/66 (66Mhz x 3.5)
  7. K6 200/66 (66Mhz x 3)
  8. K6 188/75 (75Mhz x 2.5)
  9. K6 166/83 (83Mhz x 2)
  10. K6 166/66 (66Mhz x 2.5)

Q. How does the FPU performance of the K6 compare to an equivalent Intel processor?

A. Today's most demanding applications are games and graphics packages that utilize 3-D graphics or video. Applications such as Quake have a voracious appetite for CPU clock cycles and will consume as many of them as your operating system will allow. These types of applications demand raw floating-point (FP) processing power and can bring a lesser CPU to its knees.

Although the AMD K6 includes a high performance MMX and FPU, it falls short on real world applications that use MMX or floating-point instructions. AMD did not devote as much silicon to these functions as Intel did. All of Intel's CPUs have fully pipelined MMX and FP units. AMD's MMX unit can process only one instruction at a time, while Intel's can handle two. Therefore, AMD K6 throughput on many FP operations is half that of the Intel units.

Fortunately, for those who can't afford to spend a fortune on the fastest processor available today, these applications can be enhanced - within limits - by 3-D hardware accelerators. Although this is not the way the processor manufacturers want you to think.

MMX and FPU weaknesses show up as poorer performance on the ZD 3D WinMark 97, synthetic floating point, AutoCAD, and some Photoshop tests. On most of these tests, the K6/233 is much slower than a Pentium II/233 and sometimes even slower than a Pentium MMX/233. On 3D WinMark, for example, the K6/233 delivers only about two-thirds the performance of a Pentium II/233 when using software emulation for all 3-D tasks. With a good 3-D graphics card, this gap shrinks to 18 percent, which is still considerable. Compared with a Pentium MMX/233, the K6/233 is 18 percent short on emulated 3-D, and is still 7 percent short even with a good graphics card.

In summary, a 3-D hardware accelerator may help. Check out my editorial on 3-D acceleration to determine if a 3-D hardware accelerator may be right for you. However, if your sanity depends on FP operations there is no substitute for an Intel processor.