100MHz FSB: No Longer Necessary?

We've had proof for months now that the Business Application performance of our current generation of processors is greatly dependent on the performance of the cache subsystems, from the example the Pentium II set back in 1997, to the performance of the K6-2 in 1998, without a high speed L2 cache, a processor cannot be competitive in the business world. The temporary solution to that was, of course, the 100MHz FSB, a requirement which forced older socket-7 owners to upgrade their motherboards to new Super7 boards in order to gain the performance benefits they desired. Now, with the K6-3's on-chip L2 cache, the only beneficiary of the 100MHz FSB is the L3 cache located on the motherboard, an issue which will be discussed a little later in this article.

The K6-3 will ship with support for clock multipliers ranging from 2.5x to 6.0x, in 0.5x increments, meaning that an owner of a motherboard with support for the 2.2v core voltage required by the K6-3 would be able to run a K6-3 400 at 66MHz x 6.0 without losing too much performance in comparison to an identical system running at 100MHz x 4.0. The Pentium II is a living, breathing example of this theory, in that the performance difference between a system running at a100MHz FSB and one running at a 66MHz FSB is next to nothing, with the greater performer being the chip with the faster L2 cache. Although the ideal high performance solution for anyone interested in making an upgrade to a K6-3 would be coupling the processor with a Super7 motherboard, all of those who invested in Socket-7 motherboards with support for the 2.2v core voltage yet without full Super7 compliance (i.e. no 100MHz FSB support) wont be out of luck with the K6-3. This opens up a whole new world for the low-cost socket-7 upgrade solution, unfortunately we are still bound by the 2.2v core voltage specification of the K6-3 which does considerably limit the eligibility of many older motherboards for the K6-3 upgrade.

The Socket-7/Super7 Test System Configuration was as follows:

  • AMD K6 233, AMD K6-2 300, AMD K6-2 400, AMD K6-3 450 (engineering sample)
  • FIC PA-2013 w/ 2MB L2 Cache
  • FIC PA-2013 w/ 1MB L2 Cache
  • FIC PA-2013 w/ 512KB L2 Cache
  • 64MB PC100 SDRAM
  • Western Digital Caviar AC35100 - UltraATA
  • Matrox Millennium G200 AGP Video Card (8MB)
  • Canopus Spectra 2500 TNT AGP Video Card (16MB)

The Pentium II comparison system differed only in terms of the processor and motherboard in which case the following components were used:

  • Intel Celeron 300, Intel Celeron 300A, Intel Pentium II 400, Intel Pentium II 450
  • ABIT BH6 Pentium II BX Motherboard

Running Winstone 99 under Windows 98, the Business Application performance difference between a K6-3 running at 100MHz x 4.0 and 66MHz x 6.0 is less than 2%, and definitely insignificant. If you switch benchmark suites, and use Winstone 98 which is centered much less upon multitasking performance, there is absolutely no distinguishable performance difference between the two setups.

What about in games? Using the nVidia Riva TNT chipset, a very L2 cache dependent video chipset, the performance difference between the K6-3 400/100 and the 400/66 systems is negligible as is shown by the following fps performance comparison charts.

With the performance difference never peaking above 8%, in favor of the K6-3 running at 100MHz x 4.0, even in games, the 100MHz FSB is no longer a necessity for socket-7 users to enjoy the performance they have been denied for quite some time.

Windows NT is barely any different that its younger brother in terms of its performance reaction to the 66MHz FSB instead of the 100MHz FSB with the K6-3. Windows NTs heavy reliance on a high speed L2 cache masks the 50% decrease in FSB frequency, leaving the performance difference between a K6-3 running at 100MHz x 4.0 and a K6-3 running at 66MHz x 6.0 barely above 2%.

With that settled, lets take a look at the role L3 cache plays in the overall performance of the K6-3.

Index The Benefit of L3 Cache