Introduction

Q. What is the Cyrix 6x86MX?

A. The 6x86MX is the newest generation of Cyrix processors. The 6x86MX supports Intel's MMX (Multimedia and Matrix-math eXtensions) extensions to the x86 instruction set and fits in the same motherboard socket (Socket-7) that the 6x86 uses. This means that system vendors don't have to retool their PC lines before they can start offering 6x86MX based systems. This allows them to bring 6x86MX systems to market rapidly and keep costs down.

The 6x86MX is also available retail as an upgrade chip. Users who buy a 6x86L (P55C) capable motherboard today are able to upgrade to the 6x86MX with a simple BIOS upgrade.

The 6x86MX is designed to compete with the AMD K6 and Pentium II. The Pentium II is a Pentium Pro with MMX capabilities and an external rather than built-in Level 2 cache. Unlike the Pentium Pro, however, the 6x86MX is not specifically optimized for Windows NT. It is optimized for both 16-bit and 32-bit code that is primarily found in Windows 95. I think it is a great strategic move by Cyrix to focus on Windows 95 users.

What sets the 6x86MX and Pentium II apart is the 6x86MX's compatibility with the standard 64-bit Socket-7 that the Pentium and the 6x86 plug into. Intel has finally made a major mistake in their CPU roadmap that could give Cyrix and AMD the opportunity that they have been looking for. There is no upgrade path for Pentium owners. The Pentium II requires a new motherboard, uses a new socket connector (Slot-I), and provides marginal if any performance improvement over the Pentium MMX at the same clock speed.

Cyrix's message is simple. If you have a qualified Pentium MMX/6x86L motherboard you can continue to use that motherboard for the next 12 - 18 months. The Cyrix 6x86MX is Pentium MMX/6x86L pin compatible with the only requirement being a minor BIOS modification that is needed to correctly identify the 6x86MX and setup the chipset correctly.

The Cyrix 6x86MX provides Windows 95 performance that meets and in most cases exceeds anything in AMD's and Intel’s current lineup of processors for less money and effort.

The first 6x86MXs surfaced with clock speeds from 150MHz to 188MHz.

According to the current 6x86MX roadmap, faster 6x86MX revisions are scheduled to follow early in 1998.

Q. When will the 6x86MX be available?

A. The 6x86MX is generally available worldwide.  However, expect the first shipments of future faster 6x86MX processors to initially go directly to OEMs. Approximately 4 - 6 weeks later, individual tray processors will start showing up in the retail/direct channel.   Unfortunately, this is how the system works.

Q. How much does the 6x86MX cost?

Although the 6x86MX is similar in performance to Intel's Pentium MMX and Pentium II processors, the price is decidedly different. Even Advanced Micro Devices' K6 processor, considered the low-price leader to date, costs slightly more than the 6x86MX. The 6x86MX family offers Pentium II and Pentium MMX-class performance at less than half the current per-chip pricing of Intel's offerings and below Advanced Micro Devices' K6 pricing.

Cyrix keeps its low-cost strategy after the price and positioning of the previous 6x86 chip demonstrated the difficulty of competing with Intel in the mainstream and high end. This is an extremely bright move. Cyrix's focus on the low-priced PC segment is successful because it is not an area that Intel seems intent on dominating. Even AMD has difficulty competing here.  AMD has to pay for their new fab which is weighing heavily on their balance sheet.

IBM Microelectronics manufactures Cyrix processors and sells them under their own label. Although IBM targets the same low-cost PC market as Cyrix, its processors are priced approximately 25 percent higher than Cyrix parts. IBM states that they have a policy of pricing consistently with competitors and will adjust prices accordingly when needed.

My sponsor Real World Technologies is one of the first vendors to have the 6x86MX available for sale in large quantities.

Q. What are the architectural characteristics of the 6x86MX?

IBM 6x86MXAlthough the 6x86MX is based on 6x86 core technology, the 6x86MX wrings extra performance out of slower clock speeds from architectural tweaks designed to let it handle data more efficiently and an increase in the size of the cache memory. The L1 cache has been increased from current 6x86's 16KB to 64KB, twice the Pentium II's 32K. Cache memory is integrated into the processor and can feed data to the processor at high speeds. Internal memory-management tricks reduce the need for the Cyrix chip to continually access standard RAM, which is slower than internal memory. In the 6x86MX-PR233 Cyrix uses a 75-MHz system bus which is faster than the 66-MHz bus used by Intel and AMD.

Like the 6x86, the 6x86MX chip will offer most of the Pentium Pro's most attractive features - including register renaming, out-of-order completion, and speculative execution. Unlike the 6x86, the 6x86MX will boast optimization for 32-bit code and for MMX.

MMX is an extension to the x86 instruction set that allows multiple bytes of data to be packed together in a single register and operated on simultaneously. MMX consists of 57 new instructions for speeding multimedia tasks. The trick to these new instructions is that they operate on many different data elements at once, which increases the overall amount of work the processor can do. Examples range from operating on multiple pixels in a bitmapped image to multiple sound channels in an audio stream. MMX is not intrinsically a graphics or multimedia acceleration technology, but those are the types of applications that stand to benefit most. MMX will provide a substantial performance boost for some new applications that are coded to use MMX (more so for home than for business applications).

Cyrix/IBM needed MMX and higher performance in order to stay in the CPU race with AMD and Intel. Cyrix settled an MMX trademark dispute with Intel in early April paving the way for Cyrix to call its chips MMX-compatible.

As for the FPU on the 6x86MX, there have been minor tweaks but no major improvements. However, the 6x86MX will perform context switching (changing from FPU to Integer unit when performing mixed MMX / non-MMX instructions) quicker than the P55C. Overall, at this time FPU operations are still a very small set of overall instructions in MOST applications. However, exceptions do exist. Cyrix has decided to continue concentrating on integer and MMX optimizations for the time being.

The major differences between the 6x86MX and the 6x86 processors are listed below (Taken from the Cyrix website):

Feature Comparison

Feature Comparison

Architectural Comparison

Architectural Comparison

Other notable features of the 6x86MX:

Q. How is the 6x86MX PR rating different from 6x86 PR rating?

Because the 6x86MX is architecturally more efficient that the Intel Pentium MMX and Pentium II processors, it has equivalent performance at a much lower internal clock speed. Lower megahertz speeds are an advantage, reducing power consumption and heat, making the chips more energy-efficient and more reliable. The 6x86MX has the lowest power consumption / performance ratio. This is a big change from the early days of 6x86 Classic.

Unfortunately, all of this means that we continue to have to live with the PR rating. Everyone should recognize the PR rating because it was carried over from the 6x86 Classic. Remember that PR stands for Performance Rating and not Pentium Rating. The folks at Intel are responsible for this change in meaning. They threatened Cyrix/IBM with legal action for naming their 6x86 processors Pxxx+. Intel thinks that they own the letter P and Cyrix/IBM responded by changing the name to PRxxx+.

The PR rating is determined by the Winstone 97 benchmark. As a result, it isn't a valid comparison against an equivalent Pentium MMX processor for 3D games, FPU calculations, and MMX operations.

The 6x86MX PR rating is a two tiered rating that compares the 6x86MX to both the Pentium MMX and Pentium II. The 6x86MX PR233 is compared against a Pentium II 233MHz whereas the 6x86MX PR166 and 6x86MX PR200 are compared against the Pentium MMX 166MHz and Pentium MMX 200MHz.

The PR rating used by 6x86MX is different than the PR rating used by the 6x86. A 6x86 Classic with a 150MHz internal clock speed is compared to a Pentium 200. A 6x86MX with a 166MHz internal clock speed is compared to a Pentium MMX 200. This is because the Pentium MMX is faster than the Pentium Classic.

How does the Pentium Pro fit into the PR rating? It doesn't. Cyrix/IBM don't consider the Pentium Pro to be a competitor to the 6x86MX. They are targeting the 6x86MX towards Windows 95 users. Windows 95 users don't normally buy Pentium Pros.

How does the Pentium MMX/233 fit into the PR rating?  It doesn't either.  The Pentium MMX/233 was released after the 6x86MX was introduced.   However, a 6x86MX/233 will easily outperform a Pentium MMX/233.

Personally, I think that the PR rating is a necessary evil until consumers quit associating MHz with performance. However, I also think that in its current form it is very confusing and being abused. Many have recently accused Cyrix/IBM of manipulating the PR rating to makeup for manufacturing deficiencies and trying to sell lower MHz parts at a higher cost by giving them a PR rating that they don’t deserve.

Honestly, although I understand the need for a Performance Rating, I still hate it.  In my opinion, the PR rating confuses consumers and frustrates resellers. This makes the 6x86MX more difficult to sell and less likely to be embraced. The average consumer doesn't research their purchase and relies heavily on the reseller for information and recommendations.  How would you like to be a Cyrix/IBM reseller and have to explain the PR rating to someone who knows nothing about computers Monday through Friday.  Some of the resellers can't figure it out themselves.