The IBM 6x86MX PR233

Note: For up to the minute 6x86MX information please visit my 6x86MX FAQ.

Introduction

The IBM 6x86MX PR233, although announced on May 30,1997, has been virtually absent from the marketplace. The inability of the 6x86MX partners to yield enough parts to run at 188MHz caused the general availability of the PR233 to be delayed. AMD benefited most from this delay. A lot of potential 6x86MX buyers became frustrated by the fact that they couldn't buy a 6x86MX PR233 and opted for the AMD K6/233MHz instead. You have to move fast just to stay in the same relative competitive position in the CPU business.

Finally, the manufacturing difficulties have been remedied. The first PR233s are slowly but surely starting to show up in quantities. The availability of the 6x86MX PR233 is a much needed weapon if Cyrix/IBM want to stay in the CPU race.

I spent many hours working on the IBM PR233 review. I hope you enjoy it. All I ask in return is that you continue to spread the word about Alternativecpu.com to anyone with an interest in Cyrix/IBM 6x86 or 6x86MX processors.

Caveat: This review focuses mostly on the 6x86MX PR233 and how it compares against the Pentium MMX/233. If you are looking for background information on the Cyrix/IBM 6x86MX or how the 6x86MX performs against the AMD K6 and 6x86 Classic, please read my earlier IBM 6x86MX PR200 review.

The 6x86MX PR233

The 6x86MX PR233 that I received for testing runs at 188MHz (75MHz x 2.5). I was able to successfully overclock this 188MHz 6x86MX to 200MHz and 208MHz. As a result, I will be able to give you one of the first peeks into what you can expect from the 6x86MX PR266. The 6x86MX PR266 is expected to become available Q1 1998.

How I Tested

 Components:

• IBM 6x86MX PR233
• Video board - ATI 3D Xpression+ PC2/TV 4MB EDO
• Hard drive - IBM Ultrastar 2XP 4.55GB SCSI-2
• Motherboard - Abit AX5 512K
• 32MB Memory Test - 32MB 10ns SDRAM (Macrotron)
• 64MB Memory Test - 64MB 10ns SDRAM (AMC & Macrotron)

Test condition:

• OS - Windows 95 OSR2
• Video driver - ATI Version 4.03.2162 Windows 95 display driver, 1024 x 768, 16-bit color
• The test system is loaded with Windows 95 OSR2 and benchmark programs only.
• The Abit AX5 provides 6x86MX bios support.

In order to isolate the CPU as solely responsible for any performance differences, I installed an IBM 6x86MX PR233 and Intel Pentium MMX/233 in the reference system described above. As a result, the only variable in the benchmarks was the CPU.

The Abit AX5, which is based on the Intel TX chipset, does not support linear-burst mode. The linear burst mode feature of Cyrix/IBM processors can boost 6x86MX performance by approximately 3 to 5 percent. There are no Intel chipsets, however, which support this feature.

Benchmark Tests

I ran the following tests on a IBM 6x86MX PR223 and Pentium MMX/233.

• Business Winstone 97
• High-end Winstone 97
• CPUMark 16
• CPUMark 32
• 3D Winmark 97

The 6x86MX vs. Itself

Here is what the numbers tell us:

• A 166MHz 6x86MX PR200 utilizing a 83MHz bus doesn't quite obtain PR233 performance.
• The performance of a 6x86MX running at 188MHz (75MHz x 2.5) and 200MHz (66MHz x 3) is virtual identical.
• The 6x86MX 208/83MHz is just as fast as the Pentium II/266 under Windows 95 although the 83MHz bus requirement is less than optimal.

Listed in the table below are what the PR ratings look like at various bus and internal clock speeds. Please note that IBM currently doesn't market or sell a 6x86MX that runs at 200MHz, 208MHz, or 225MHz.

The 6x86MX PR233 with 32MB vs. 64MB of SDRAM

There is minimal gain in the Business Winstone score when upgrading from 32MB to 64MB of RAM under Windows 95. However, this is not true under Windows NT. Because Windows NT occupies a larger memory footprint, the extra memory will significantly improve performance.

Windows 95 will still perform much better with 64MB of memory than the Winstone score reflects because faster processors can take advantage of extra memory. The hard drive's involvement is reduced because there is less need for a swap file. As a result, the CPU's power becomes more evident. Data can be swapped from memory much faster than it can be swapped from the hard drive.

The 6x86MX vs the Pentium MMX

The 6x86MX PR233 is 8% percent faster than the Pentium MMX/233 on the Business Winstone, although on the High-end Winstone it is only 1 percent faster. The performance edge that the 6x86MX held over the Pentium MMX/233 on the Business Winstone shrank on the High-end Winstone because the Intel FPU architecture is more proficient than the 6x86MX FPU architecture in processing floating point calculations. The 6x86MX is optimized for business software which relies less on floating point calculations and more on integer calculations.

Just as you wouldn't judge a car's performance based on the peak engine RPM, you shouldn't judge a microprocessor's performance by its clock speed. This issue is especially important for Cyrix/IBM because the 6x86MX is offered at slower clock speeds than microprocessors from AMD and Intel. Because the 6x86MX is architecturally more efficient its competitors, it provides equivalent performance at a much lower internal clock speed. The Intel and AMD approach, in which x86 instructions are translated into RISC-like internal instructions, enables higher clock rates, but delivers less performance per clock cycle. As indicated by the CPUMark16 and CPUMark32, nobody delivers more performance per clock cycle than Cyrix/IBM.

FPU and MMX Performance

Five years ago, when Cyrix began the 6x86 design, no mainstream applications were impacted by floating-point performance. Now, however, the emergence of 3-D games and 3-D consumer CAD applications has brought floating-point units into the mainstream.

The MMX and floating-point performance better differentiates the 6x86MX PR233 and Pentium MMX/233. The two places where Cyrix's performance falls short are floating-point and MMX instructions. Intel chose to implement a high-performance floating-point unit (FPU) and dual MMX units, whereas Cyrix (and AMD) opted for a simpler floating-point unit and a single MMX unit. Intel's FPU is fully pipelined, which means that it can start a new floating-point operation every clock cycle. Cyrix's and AMD's FPUs are not.

FPU performance is also heavily dependent on the CPU clock speed and the bus speed is much less important. This is because the FPU is not struggling to get data over the bus, but working heavily to complete the calculations.

The 6x86MX results in 3-D performance that is terrible when compared to the Pentium MMX/233. Even with my ATI 3D Xpression+ (Rage II) graphics card, the gap remained a substantial 44% percent, making the 6x86MX the worst choice for 3-D and MMX operations.

A 3-D accelerator can help alleviate this deficiency depending on the types of 3D applications that you use. Find out if a 3-D accelerator is right for you.

Power Consumption

Less watts of power generated means there is less heat to deal with. In this case, less is more. Less heat increases your chances of overclocking. The 6x86 Classic was crucified because of its power requirements and the heat that it generated. Now look at the graph and see who is running a temperature. The 6x86MX has one of the lowest power consumption/performance ratios. The lower megahertz speeds of the 6x86MX are an advantage, reducing power consumption and heat, making the chips more energy-efficient and reliable.

Have you ever seen the heatsink provided with the Pentium II? It is so big that you could use it as a skillet!

Other Specifications

Conclusion

To make the best processor selection, you need to decide what kinds of applications are important to you. CPU performance varies considerably from one application type to another. If the applications that are important to you depend on floating-point or MMX code, the PR rating may be misleading. For some applications, a 6x86MX-PR233 could perform more like a 200MHz or 166MHz MMX Pentium. In my humble opinion, unless all you do is play games and use high-end 3D applications you are throwing your money away if you buy a Pentium MMX. The IBM 6x86MX PR233 hangs the Intel Pentium MMX/233 out to dry on most business and productivity applications.

Cyrix/IBM isn't going to blow the AMD K6 or the Intel Pentium II away with the 6x86MX PR233, but this CPU should enable Cyrix/IBM to increase its market share and continue to build a profitable niche. Once you have decided to consider non-Intel processors, choosing between the 6x86MX and the K6 may be tough. Both are priced well below Intel's offerings, perform well on most mainstream applications, and are weak on MMX and floating-point applications. If you want top performance and are willing to pay top price, then the Pentium II is still king.

Price/performance is what I preach and this is the biggest selling point of the 6x86MX. Cyrix/IBM continue to own this. If you don't require maximum performance on 3-D, image-processing, or similar applications, the 6x86MX is a great value.

This page has been accessed times since Wednesday, October 15, 1997.