IIIrd Time May Not be the Charm

Many end users have been eagerly awaiting the introduction of the Pentium III or the K6-III, anticipating a simple processor drop in to gain all of the performance benefits. Tom’s Hardware Guide published a set of benchmarks showing that the K6-III excels at integer operations, while the Pentium III achieves amazing gains in floating point and games performance. Unfortunately what was not said were that there are some specific requirements necessary to support these processors, and to realize the performance benefits.

Pentium III Requirements

Most people are aware that the Pentium III introduces 70 new instructions that provide increased performance for 3D applications and games. Some of these (SIMD-FP) are make use of new floating point capabilities, while others (memory streaming) change the way the cache is utilized. It seems that most reports have indicated if the user has DirectX 6.1 installed, that these features are available and any application that implements the instructions will now run faster. Unfortunately, this is not necessarily the case.

The memory streaming instructions enable the processor to bypass L1 and/or L2 cache, if that option is chosen by the developer. These instructions are most useful when the application developer knows that the data being read will only be used once, which will be the case for many 3D games. There are also memory prefetching instructions which allow memory to be pre-loaded into cache before it is actually used, and can be used with non-sequential ranges of memory. In order to take advantage of the new cacheing features, the motherboard BIOS must support them. If this BIOS support is not present, the end user will not realize any of the performance gains, since the cache will operate as if these features were not implemented.

Approximately 50 of the new instructions are called SIMD-FP instructions. The original MMX instructions used the same registers as the FP unit, which caused a 70 clock delay when switching between normal FP instructions and MMX instructions. The new SIMD-FP instructions make use of 8 new registers included in the processor to allow parallel FP and integer operations, and therefore are much faster. Unfortunately, the use of these registers requires OS support. Windows98 and Windows 2000 natively support these registers. Windows NT 4.0, Linux 2.3 and a few other operating systems (Netware, Solaris and UnixWare) will support them with the proper updates and drivers. The bad news is that Windows 95 does not have support for these registers. This means that the applications using these instructions may not install, or will not function if they do install.

One final issue with the Pentium III processor is its power requirements. At 2.0V the processor draws as much as 18 Amps! If the motherboard does not have voltage regulators that will handle this current, the motherboard may be damaged. This also should be a warning to potential overclockers, as raising the MHz also raises the current. Before pushing the processor too far, it would be advisable to contact the manufacturer and find out what the voltage regulators are designed to handle.

K6-III Requirements

There may be an issue with the K6-III and the VIA MVP3 chipset, though no official word has been given on this. As of this writing, only ALi based motherboards are on the K6-III approved motherboard list, and some motherboard manufacturers have mentioned that their boards have been unstable when both L2 and L3 cache are enabled. Recent information seems to indicate that the BIOS on these motherboards needs to be updated to overcome this problem.

Prior to the AMD K6 processors, motherboard voltages were limited and fairly well known (i.e., 3.5V, 3.3V and 2.8V). AMD added several new voltages over the past two years, including 3.2V, 2.9V and 2.2V. Due to the power requirements of the on-die L2 cache, the K6-III has once again added a new voltage requirement of 2.4V, with a ‘safe’ range of 2.3V to 2.5V. Unfortunately, many motherboard manufacturers did not recognize this trend and included a limited number of voltage settings on their boards that did not include these voltages.

Even if the motherboard supports the proper voltage, the amperage may be an issue. While the K6-III does not have the current draw of the Pentium III, it does exceed what many boards were designed for. Until recently, most voltage regulators on Socket 7 motherboards were designed to handle a 10 Amp current, however the K6-III draws as much as 12.5 Amps. As with the Pentium III boards, if the voltage regulator was not designed for this load, the motherboard could be damaged, and overclockers should be aware that pushing the CPU too far could cause similar problems.


It should be apparent that before selling, recommending or installing either of these processors the proper preparations should be performed. Failing to pay attention to these matters could result in unsatisfied customers, increased RMAs, damaged components, and of course additional costs for both the vendor and the end user. It may not be easy to find some of the information, such as voltage regulator ratings, but we will attempt to provide updates as time permits and as the information is discovered.

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