KarbosGuide.com. Module 3e.04

About P6-like processors from AMD and Cyrix

The contents:

  • AMD's powerfull K6
  • AMD's K6-2
  • Cyrix 6x86MX
  • Pure CISC
  • Two brands of 6X86MX
  • K6-2
  • Next page
  • Previous page

  • K6

    Intel's Pentium II soon got competition from AMD and Cyrix. Both companies have launched several good processors, sometimes giving Intel a hard competiton.

    AMD's K6 is from April 2, 1997. In 1996 AMD produced the K5 processor which was not very impressive, however very cheap. The company was put back to business by Mr. Atiq Raza, who brought in the technology from NexGen. This lead to the very successful model K6, which saved AMD from ruin.

    The market soon discovered that the K6 performed a lot better than Pentium MMX, which it shared the Socket 7 motherboards with. Here are the data:

  • Equipped with 32+32 KB L1 cache and MMX.
  • Containing 8.8 million transistors.

    K6 is (like K5) compatible with Pentium. Thus, it can be mounted in a Socket 7 on a regular Pentium motherboard, and this soon made the K6 very popular.

    BIOS and voltage

    On the older motherboards, it is possible that the BIOS has to be updated to make it work. K6 performs best when the BIOS recognizes the chip, so its full potential can be utilized. That requires a dual voltage motherboards. The K6-200 requires 2.9 volt for its core. The other models require 2.8 volt as the Pentium MMX.

    The K6 model 7 (Little Foot) was running at 300 MHz. These high performance K6s were sold at very reasonable prices. The problem seemed in the beginning to be to produce enough chips. The K6 was followed by the K6-2 (and later the Athlon), which gave AMD an enormous success in the late 1990's.

    Cyrix 6X86MX (MII)

    Cyrix was a company with another high performance chips, placed somewhere between 5th and 6th generation. The first models were positioned against the Pentium MMX chip from Intel. Later models can be compared to the K6. I have to admit, that I quite seldom saw these processors in my country, but they did exist.

    Cyrix powerful P6-classed processor was announced as the "M2". Introduced on May 30, 1997 the name became 6X86MX. Later it has been named MII again. There has always been some confusion about the identification of the Cyrix CPUs.


    This 6X86MX chip is compatible with the Pentium MMX. This gives additional possibilities to assemble PCs on ordinary Socket 7 motherboards.

    The 6X86MX has 64 KB internal L1 cache, which is very impressive. Cyrix also utilizes technologies which are not found in Pentium MMX. These chips are named to compare them with genuine Pentiums, although their internal clock speed is lower than corresponding Intel processors.

    Pure CISC

    The 6x86MX was unique compared to the other 6. generation CPUs (Pentium II and Pro and K6) since it does not work upon a RISC kernel. 6x86MX executes the original CISC instructions as does the Pentium MMX.

    The 6x86MX has plenty of internal registers placing it in company with other 6th generation CPU's:

    CPU Number of
    32 bit CPU registers
    Pentium MMX 8
    6x86MX 32
    Pentium Pro 40
    K6 48

    The 6x86MX had - as all processors from Cyrix - a problem concerning the FPU unit. However, only using standard office applications, this is of no concern. The problem arises when you play 3D games.

    Poor performance

    The 6X86MX is quite a powerful chip - on the paper. However, there are problems with the supply of them, and also the system bus speed caused troubles. It was difficult to find a motherboard that accepts these speeds. They also lacked good FPU and MMX performance. They did not incorporate the 3DNow! technology. Hopefully this will change as Cyrix has been taken over by VIA.

    6X86MX Internal speed External speed
    PR166 150 MHz 60 MHz
    PR200 166 MHz 66 MHz
    PR233 188 MHz 75 MHz
    PR266 225 MHz 75 MHz
    PR300 233 MHz 66 MHz
    PR333 255 MHz 83 MHz
    PR433 285 MHz 95 MHz
    PR466 333 MHz 95 MHz

    It was evident that Cyrix intended to continue this line of processors, and this definitely was a positive trend. Intel got competition, and it keept the well tested and inexpensive Socket 7 motherboards in the market. In 2000 the VIA Joshua processor will hold designs originating from Cyrix - ported into socket 370 design.

    Two brands of 6x86MX and MII

    The 6x86MX processor was produced by National/Cyrix as well as by IBM. The architecture were the same, but the chips were built at different plants.

    On April 14, 1998 the Cyrix MII (M-two) version was launched. It was exactly the same chip as the 6X86MX just running at higher clock frequencies. Later the voltage will be reduced to 2.2 Volts.

    IBM used a new technology for their PR333 chip. It is patented and called Flip-Chip. The die is soldered directly to the ceramic casing and this causes less induction.

    Cyrix MIII

    In the year 2000 we were expecting the 3rd generation of the 6X86MX (code name Jalapeno and Mojave). This CPU was to be named MIII, and to come in>600 MHz flavors. The MXi was intended Socket 7 compatible, with a core running on a 133 MHz system bus. It also should include 3DNow! instructions and improved FPU. Read more on this.

    AMD K6-2


    The next AMD "model 8" version of the K6 had the code name "Chomper".

    This processor of May 28, 1998 was marketed as K6-2, and like the model 7 version of the original K6, it is manufactured with 0.25 micron technology. These chips run on just 2.2 Voltage. They became an immense succes, in many situations competing very successfully with Intel's Pentium II.

    Super 7 motherboards and better MMX

    The K6-2 is made for a front side bus (system bus) at the speed of 100 MHz. This is to be found with the so-called Super 7 motherboards. AMD made other vendors like VIA produce new chipsets for the traditional socket 7 motherboards, after Intel in 1997 had given up the platform.

    K6-2 is also improved with an MMX performance twofold better compared to the original K6.


    The K6-2 holds a new 3D plug-in (called 3DNow!) for better game performance. It consists of 21 new instructions that can be used by software developers giving a better 3D-performance. To benefit from it, you need a graphics driver or a game, which deals directly with the new commands.

    The good thing is, that games do not have to include special programming to benefit from 3DNow!. Support is included in DirectX 6.0 (and newer) for Windows . DirectX is a so-called multimedia API (in fact a hardware abstraction layer) for Windows . It is some programs that can enhance the multimedia performance within all Windows programs.

    3DNow! is not compatible with MMX, but the K6-2 holds MMX as well as the 3DNow!. Also Cyrix and IDT launch CPUs with 3DNow!. Read more on 3DNow!

    Good and inexpensive power

    The K6-2 gave very, very good performance. You can compare the models to the Pentium IIs. A K6-2 350 MHz performed very similar to a Pentium II-350, but was sold a lot cheaper. And you even saved more because of the cheaper motherboard.

    100 MHz bus

    Not all K6-2s ran with a 100 MHz bus. Here you see some of the versions, which require motherboards with crystals capable of these configurations:

    K6-2 Bus Clock
    266 MHz
    66 MHz
    4.0 X 66 MHz
    266 MHz
    88 MHz
    3.0 X 88 MHz
    300 MHz
    100 MHz
    3.0 X 100 MHz
    333 MHz
    95 MHz
    3.5 X 95 MHz
    350 MHz
    100 MHz
    3.5 X 100 MHz
    380 MHz
    95 MHz
    4.0 X 95 MHz
    400 MHz 100 MHz 4.0 X 100 MHz

    Two of the CPU's in the table must be the same. AMD calls it a 350 MHz version, but in Denmark e.g it was sold as a 380 MHz version.

    K6-2/400 and above

    November 15, 1998. The K6-2/400 was introduced. This chip worked on a new core, which should be slightly improved. Hence the performance matched a Pentium II-400.

    April 6, 1999. A 475 MHz version of the K6-2 was introduced. The latest version is 533 MHz.

    AMD had 39% of the market with K6-2 in 1999!

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    Learn more

    Read about chip sets on the motherboard in module 2d

    Read more about RAM in module 2e

    Read module 5a about expansion cards, where we evaluate the I/O buses from the port side.

    Read module 5b about AGP and module 5c about Firewire.

    Read module 7a about monitors, and 7b on graphics card.

    Read module 7c about sound cards, and 7d on digital sound and music.

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