PerformancePerformanceQ. Does the Intel Triton FX, Triton HX, Triton VX, and Triton TX offer optimal performance for Cyrix 6x86 processors?
A. No, the Triton FX, Triton HX, Triton VX, and Triton TX chipsets aren't optimized for the 6x86. This should not be surprising since they are designed and manufactured by Intel. These chipsets don't support the 6x86's linear burst mode which, if supported, should boost CPU performance by approximately 3 to 5 percent. Intel chipsets also do not officially support a 75 MHz bus which is required for a Cyrix 6x86 PR200+ processor.
There are many chipsets from VIA, VLSI, and SiS that support both of these things. The problem is that it is more difficult to find a motherboard that uses these chipsetsl. Check out the Real World Technologies website for a list of motherboards supporting the 75MHz bus speed.
Many people have asked why I bought a Tyan Tomcat I motherboard if it is not optimized for the Cyrix 6x86. The Tomcat I is based on the Triton HX chipset. It is incorrect to assume that because you use a motherboard which is based on a chipset that isn't optimized for the Cyrix 6x86 that it will not perform well. This is absolutely not true.
There are performance differences between motherboards and chipsets just like there are between graphics cards. Some motherboards are faster than others as a result of a better motherboard design. That is why my Tomcat I can perform extremely well and not be based on a chipset designed for the 6x86.
A disadvantage of the Tomcat I is that I can never upgrade to a Cyrix PR200+ because the Triton HX does not officially support the 75 MHz bus.
Get all of the details about my upgrade, including a multimedia benchmark comparison of my system and 101 Pentium class PCs tested by PC Labs, at my personal Cyrix 6x86 upgrade experience page.
Q. What's the deal with the PR rating and why does it exist?
A. Clock frequency (MHz), while important, is no longer an accurate or consistent measure of CPU performance. Architectural differences between processor designs add another variable to the equation. Case in point, the Cyrix PR166+ is actually clocked at 133 MHz internally, but performs faster in real world applications than an Intel P166 which is clocked at 166 MHz internally. Unfortunately, as a result of Intel's domination of the microprocessor market, Joe Average Consumer is conditioned to think that if a chip has a higher clock frequency then it must be faster. So Joe probably thinks that a Cyrix 133 MHz must be slower than a Pentium 166 MHz and makes buying decisions based upon this information even though the argument is not always a valid one.
As a result, the PR-rating concept was jointly developed by Cyrix, IBM Microelectronics, SGS-Thomson Microelectronics, and Advanced Micro Devices (all Intel competitors who are affected by this way of thinking) to establish a performance rating relative to the internal frequency of a Pentium processor. With the PR-rating in place, Joe can easily evaluate a Cyrix 6x86 processor and understand that a Cyrix processor with a PR166 rating would have performance comparable to a 166 MHz Pentium processor regardless of its actual clock speed and without scrutinizing the architectural merits of the different processors.
The Winstone 97 benchmark is used to determine the PR rating.
Q. Why should I care about the system bus speed?
A. The Cyrix PR200+ provides a classic example of why you shouldn't base performance predictions solely on a chip's internal processing speed. For example, the Cyrix PR200+ has an internal processing speed of 150 MHz. That is much slower than 200-MHz internal processing speed of the Intel P200, but the Cyrix chip still performs faster. Its advantage has as much to do with the system bus as with the chip. The Cyrix PR200+ has a 75-MHz system bus whereas the Intel P200 has a 66-MHz system bus. The 75-MHz system bus means that data leaving the CPU doesn't slow down as much as it does when leaving a 66-MHz system bus.
Bus speed is increasingly becoming a bottleneck in today's systems. It doesn't matter how fast the CPU can process data if it must constantly wait on the system bus to finish moving it. That is why you see a large increase in system performance between an Intel P133 and P166, but only a very small (approximately 10%) increase in performance between an Intel P166 and P200. The Intel P200 processor has pushed the 66 MHz bus to its limit. That is why Cyrix decided to push the technology envelope forward and started using a 75 MHz bus speed for its PR200+.
Pushing the bus speed to 75 MHz is not without its headaches. The biggest problem has been the limited availability of chipsets and system boards that support it. Cranking up the bus speed can make life more difficult for the motherboard designer.
Processor Part No Performance Rating Bus/Clock Speed 6x86-PR200 PR200+ 75/150 MHz 6x86-PR166 PR166+ 66/133 MHz 6x86-PR150 PR150+ 60/120 MHz 6x86-PR133 PR133+ 55/110 MHz 6x86-PR120 PR120+ 50/100 MHz
Beyond the system bus speed, Cyrix 6x86 processors also benefit from a more advanced architecture than the Pentium. It takes instructions and performs them more optimally.
I personally would never buy a Pentium class processor that required a bus speed below 66 MHz. This criteria would eliminate any Cyrix chip below the PR166+. The performance hit just isn't worth it. Unfortunately, Intel and Cyrix are aware of this and chip prices reflect it. Now you know why a PR150+ is so much cheaper than a PR166+. It is because a PR150+ uses a 60 MHz bus. Yuck.
Q. How poor is the Cyrix 6x86 FPU performance?
A. Thanks go to Toshiyuki Saito for giving me a education on the Cyrix and Pentium floating point units.
I have received many questions from readers who want to know how the Cyrix 6x86 FPU performs. The word is out that the FPU on the 6x86 is weak. This is somewhat of a misstatement.
The Cyrix 6x86 FPU is not incompatible or terribly slow - it just doesn't have the same or better FPU performance as an equivalent Pentium. For example, a Cyrix 6x86 PR166+ could not perform as well as an Intel P166 when running applications such as CAD and Quake that rely heavily on the FPU.
The 6x86 cannot execute multiple FPU instructions simultaneously, while the Pentium can. The 6x86 can only send one FPU instruction into the CPU pipe and the following FPU instructions must wait in the queue. The 6x86 can, however, execute both a FPU and integer instruction simultaneously. The Pentium can pump one FPU instruction into the CPU pipe each clock cycle and executes FPU instructions simultaneously if certain conditions are met. The Pentium clearly has the better architecture in terms of FPU execution, just like the 6x86 is superior in other features (register renaming, speculative execution, etc.). Therefore, it is wrong to argue that the 6x86 PR166+ FPU = Pentium P133 and generalize that the 6x86 PR166+ FPU = Pentium P90 in real world performance. It all depends on what types of applications that you run. Regardless, it is not unrealistic to expect a 20% - 50% performance decrease in FPU operations depending on the application.
FPU performance is an area where the PR rating fails to make an accurate comparison between the Cyrix 6x86 and the Pentium.
Cyrix decided to concentrate on integer performance instead. One reason Cyrix did this is because the most commonly used games and applications in Windows don't use FPU. These applications depend on integer operations. Cyrix was able to better Intel in this area.
Q. Why do all of these Cyrix 6x86 optimizers exist and are they beneficial?
A. The answer is it depends. All motherboards have a BIOS. A quality motherboard will come with a good BIOS and frequent BIOS updates. The BIOS does influence the overall system performance and manufacturers optimize the BIOS for motherboards they sell. The best bet for a stable 6x86 system is to use a board that comes 6x86 enabled and use the settings that the BIOS provides. The BIOS, however, may be setting some processor register bits conservatively by default to guarantee functionality at the expense of performance. The Cyrix 6x86 optimizers "tweak" the 6x86 register settings and can result in a 5-10% performance increase in certain cases. This is all dependent on the BIOS.
Some of the 6x86 optimizer programs that claim to boost the 6x86 performance can be dangerous to use. Yes, they do give you more performance but at a price. Self modifying code sometimes found in games software will usually trip up when the 6x86 registers are manipulated for more performance. Cyrix wouldn't simply leave anything out that enhanced performance unless the drawbacks/side effects were damaging.
If you don’t mind the possibility of your system misbehaving, then go ahead and play with the optimizers and see if you gain performance. Rebooting the machine will reset the registers back to their default settings and running an optimizer does not cause any permanent changes.
You can find many Cyrix 6x86 optimizers on my Files & Utilities page.
