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A Guide To AMD Processors
K5 / K6 / K6-2 / K6-3 / K7


General Overview

Advanced Micro Devices (AMD) is the world's second largest supplier of Windows compatible PC processors. A prominent competitor in the 386 and 486 era, AMD's market share sharply declined when it failed to respond promptly to the release of the Intel Pentium processor. It was only later, with the release of the K6 processor, that AMD finally managed to make a slow come back to the scene.

  • The AMD X5 processor

    Released as the X5/133. This is a 486DX with a 4 times clock multiplier. It fits in a 486 socket and runs at 133MHz.


  • The AMD K5 processor

    The processor uses a Pentium class socket. This chip was introduced very late in the pentium processor wars and was described as too little too late. Moreover, it's floating point performance (FPU) is still slower than the floating point performance (FPU) of the Pentium, but it's FPU performance was still better than that of the Cyrix/IBM 6x86.

    		•

    AMD K5 Processor Clock Speeds and Multipliers
    CPU Clock Speed/MHz Bus Speed/MHz Multiplier
    K5 PR75 75 50 x1.5
    K5 PR90 90 60 x1.5
    K5 PR100 100 66 x1.5
    K5 PR120 90 60 x1.5
    K5 PR133 100 66 x1.5
    K5 PR166 116 66 x1.75


    Note: With respect to this processor, there are some interesting things to take note of. First is the strange 1.75x clock multiplier of the K5 PR166. This is an internal clock multiplier that will activate when a 2.5x motherboard setting is used. The other strange thing is that the PR120 runs at a lower clock speed than the PR100. This implies that the core of the PR120 - PR166 K5 processors is slightly different from that of the lower models.


  • The AMD K6 processor

    The AMD K6 Processor
    AMD K6 processor

    Designed by the NexGen team that was bought over by AMD, it held the title of the fastest x86 processor for only a few weeks before the launch of Intel's Pentium 2 processor. This 8.8 million transistor processor is MMX enhanced and has 64KB of internal level 1 cache. Although not superscaler, it has a well designed FPU that can outperform the Pentium MMX under certain conditions. Needless to say, its FPU cannot quite match up to the dual FPU units of the Pentium 2. This processor fits in a Pentium class (socket 7) motherboard and is a very good all rounder. Early versions were built by a 0.35 micron five layer metal silicon process technology. Later, the size was reduced to 0.25 microns on the K6-2 and K6-3 versions. The reduction in size enables the K6-2 and K6-3, at 266MHz, to consume only 8W of power, making it an ideal processor for notebooks.

    • AMD-K6 MMX(TM) Enhanced Processor Competitive Comparison

    Processor Features
    AMD K6
    Pentium II
    Pentium Pro
    Pentium MMX
    RISC core
    Yes / 6 issue
    Yes / 5 issue
    No
    Superscalar Yes
    Speculative execution
    Yes
    No
    Out of order execution
    Yes
    No
    Data forwarding
    Yes
    No
    Register renaming
    Yes
    No
    x86 decoders
    2 sophisticated,
    1 long, 1 vector
    1 sophisticated, 2 simple
    1 sophisticated, 1 simple
    Execution pipelines
    6
    5
    2
    Branch prediction
    Yes
    Advanced 2 level branch prediction
    Yes
    No
    Branch history table entries
    8,192
    512
    256
    Branch target cache entries
    16
    0
    Branch prediction accuracy
    95%
    90%
    75-80%
    Executes MMX technology
    Yes
    No
    Yes
    High performance floating point
    Yes
    L1 instruction and data cache
    32K + 32K
    16K + 16K
    8K + 8K
    16K + 16K
    Industry compatible SMM
    Yes
    Latency (smaller is better)
    2 clock
    5-7 clock
    2 clock

    The RISC86 microarchitecture internally decodes x86 instructions into RISC86 operations. This provides simpler, fixed-length opcodes that can be executed much faster than by directly executing complex x86 instructions. The K6 is fully compatible with the Windows 95, Windows NT, Windows 3.x, MS-DOS®, Novell® NetWare®, OS/2 Warp, and Unix.

    The performance problem with the MMX unit faced by the Intel Pentium MMX due to the shared registers used by both FPU and MMX also applies to the K6. However, due to lower latency figures (3x faster than the Pentium MMX), this is less of a problem with the K6.



  • The AMD K6-2 processor (aka. K6 3D)

    Released on May 28th 1998 and running at 300MHz and upwards, the K6 3D, which is built by a 0.25 micron die process, features superscalar dual MMX units and a new multimedia instruction set known as 3D Now!. This processor runs at a VCore of 2.2V and has a transistor count of 9.3 million transistors. This processor enables accelerated and enhanced graphics with full-featured MPEG-2 video and AC-3 sound.

    • The key features of the K6 3D are:

  • 100 MHz Local Bus
  • 3D Now! Instruction Set (21 instructions)
  • Support for SIMD operations
  • Superscalar Dual MMX Unit

    		•  AMD K6-2 Processor
    Designed primarily with gaming in mind, AMD's 3D Now! instruction set, accelerates graphics, audio and multimedia applications and is supported by Microsoft's DirectX (DirectX 6.0) and many 3D game developers. Unlike switching from FPU to MMX instructions, there is no switching overhead involved between MMX and AMD 3D Technology instructions.

  • The AMD K6-3 processor (aka. K6+ 3D)

    A further enhanced version of the K6-2, this processor has a built-in 256Kb of Level 2 cache that operates at the processor frequency. Having 21.3 million transistors and a die size of 135 mm˛, due to its 0.25 micron manufacturing process, it is still smaller in size than the original 8.8 million transistor K6 processor. It will support an external motherboard cache (Level 3) for enhanced performance while maintaining Socket 7 compatibility. The highest speed that this processor is expected to reach is 450 megahertz. Date of release is the beginning of 1999. Rumours say that lab samples of the K6-3 at AMD are running 30% faster than a similarly clocked Pentium 2 processor.

  • The AMD K7 Processor (Argon)

    Running at speeds of 500MHz and above, although this processor will be mechanically interchangeable with Intel's Slot 1 design, it will require the electrical bus protocols of the Alpha EV-6 processor. This new slot design is called Slot A by AMD and it will be directly interchangable with Digital's Alpha 21264 processor cartridges. The Slot A design will allow for much higher clock frequencies than socket 7 and has multiprocessor support. The new design will also support a maximum bus speed of 333MHz between the K7 processor and the core-logic chip on the motherboard. This compares to the mere 100MHz of the Intel Pentium 2's 440BX chipset. Although not in the specification, its flexibility allows for a Level 2 cache to be added through a back-side bus. The EV-6 has a bandwidth of 2.6GBps at 333MHz. The K7 will not work with existing Intel motherboard chipsets such as the Intel 440LX and 440BX.

    The expected date of release is early 1999 and the K7 is expected to compete with Intel's 7th generation processors. The processor will initially feature aluminium interconnects, but this will be upgraded to the faster copper interconnects in the middle of year 2000. The K7 will be manufactured by Motorola due to a cross-manufacturing alliance between the two companies.


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    Last modified on February 19, 1998