Intel-Compatible Processors (AMD and Cyrix)
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Intel-Compatible Processors (AMD and Cyrix) Several companies²mainly AMD and Cyrix²have developed processors that are compatible with Intel processors. These chips are fully Intel-compatible, so they emulate every processor instruction in the Intel chips. Many of the chips are pin-compatible, which means that they can be used in any system designed to accept an Intel processor; others require a custom motherboard design. Any hardware or software that works on Intel-based PCs will work on PCs made with these third-party CPU chips. A number of companies currently offer Intel-compatible chips, and I will discuss some of the most popular ones here. AMD Processors Advanced Micro Devices (AMD) has become a major player in the Pentium-compatible chip market with its own line of Intel-compatible processors. AMD ran into trouble with Intel several years ago because its 486-clone chips used actual Intel microcode. These differences have been settled and AMD now has a five-year cross-license agreement with Intel. In 1996, AMD finalized a deal to absorb NexGen, another maker of Intel-compatible CPUs. NexGen had been working on a chip it called the Nx686, which was renamed the K6 and introduced by AMD. Since then, AMD has refined the design as the K6-2 and K6-3. Its newest chips, called the Athlon and Duron, are designed similarly to the Pentium II/III and Celeron and use a similar but not identical cartridge or slot design. AMD currently offers a wide variety of CPUs, from 486 upgrades to the K6 series and the Athlon/Duron. Table 3.20 lists the basic processors offered by AMD and its Intel socket. Table 3.20 AMD CPU Summary CPU Type P- Actual Clock Motherboard CPU Socket Rating CPU Multiplier Speed or Slot Speed (MHz) (MHz) Am486DX4-100 n/a 100 3x 33 Socket 1,2,3 Am486DX4-120 n/a 120 3x 40 Socket 1,2,3 Am5x86-133 75 133 4x 33 Socket 1,2,3 K5 PR75 75 1.5x 50 Socket 5,7 K5 PR90 90 1.5x 60 Socket 5,7 K5 PR100 100 1.5x 66 Socket 5,7 K5 PR120 90 1.5x 60 Socket 5,7 K5 PR133 100 1.5x 66 Socket 5,7 K5 PR166 116.7 1.75x 66 Socket 5,7 K6 PR166 166 2.5x 66 Socket 7 K6 PR200 200 3x 66 Socket 7 K6 PR233 233 3.5x 66 Socket 7 K6 PR266 266 4x 66 Socket 7 CPU Type P- Actual Clock Motherboard CPU Socket Rating CPU Multiplier Speed or Slot Speed (MHz) (MHz) K6 PR300 300 4.5x 66 Socket 7 K6-2 PR233 233 3.5x 66 Socket 7 K6-2 PR266 266 4x 66 Socket 7 K6-2 PR300 300 4.5x 66 Socket 7 K6-2 PR300 300 3x 100 Super7 K6-2 PR333 333 5x 66 Socket 7 K6-2 PR333 333 3.5x 95 Super7 K6-2 PR350 350 3.5x 100 Super7 K6-2 PR366 366 5.5x 66 Socket 7 K6-2 PR380 380 4x 95 Super7 K6-2 PR400 400 6x 66 Socket 7 K6-2 PR400 400 4x 100 Super7 K6-2 PR450 450 4.5x 100 Super7 K6-2 PR475 475 5x 95 Super7 K6-2 PR500 500 5x 100 Super7 K6-2 PR533 533 5.5x 97 Super7 K6-2 PR550 550 5.5x 100 Super7 K6-3 PR400 400 4x 100 Super7 K6-3 PR450 450 4.5x 100 Super7 Duron PR550 550 5.5 100* Socket A Duron PR600 600 6 100* Socket A Duron PR650 650 6.5 100* Socket A Duron PR700 700 7 100* Socket A Athlon PR500 500 5x 100* Slot A/Socket A Athlon PR550 550 5.5x 100* Slot A/Socket A Athlon PR600 600 6x 100* Slot A/Socket A Athlon PR650 650 6.5x 100* Slot A/Socket A Athlon PR700 700 7x 100* Slot A/Socket A Athlon A PR750 750 7.5x 100* Slot A/Socket A Athlon PR800 800 8x 100* Slot CPU Type P- Actual Clock Motherboard CPU Socket Rating CPU Multiplier Speed or Slot Speed (MHz) (MHz) A/Socket A Athlon PR850 850 8.5x 100* Slot A/Socket A Athlon PR900 900 9x 100* Slot A/Socket A Athlon PR950 950 9.5x 100* Slot A/Socket A Athlon PR1000 1000 10x 100* Slot A/Socket A Notice in the table that for the K5 PR120 through PR166 the model designation does not match the CPU clock speed. This is called a PR rating instead and is further described earlier in this chapter. Starting with the K6, the P-Rating equals the true MHz clock speed. The model designations are meant to represent performance comparable with an equivalent Pentium-based system. AMD chips, particularly the new K6, have typically fared well in performance comparisons and usually have a much lower cost. There is more information on the respective AMD chips in the sections for each different type of processor. As you can see from the table, most of AMD's newer K6 series processors are designed to use the Super7 interface it pioneered with Cyrix. Super7 is an extension to the standard Socket 7 design, allowing for increased board speeds of up to 100MHz. The AMD Athlon (K7) processors are designed to use Slot A, which is a 242-pin slot similar in appearance, but not in the pinout, to the Intel Slot 1. Cyrix Cyrix has become an even larger player in the market since being purchased by National Semiconductor in November 1997 and by VIA Technologies in 1999. Prior to that it had been a fabless company, meaning it had no chip-manufacturing capability. All the Cyrix chips were manufactured for Cyrix first by Texas Instruments and then mainly by IBM up through the end of 1998. Starting in 1999, National Semiconductor has taken over manufacturing of the Cyrix processors. More recently, National has been purchased by VIA technologies, who still uses National to manufacture the chips. Like Intel, Cyrix has begun to limit its selection of available CPUs to only the latest technology. Cyrix is currently focusing on the Pentium market with the M1 (6x86) and M2 (6x86MX) processors. The 6x86 has dual internal pipelines and a single, unified 16KB internal cache. It offers speculative and out-of-order instruction execution, much like the Intel Pentium Pro processor. The 6x86MX adds MMX technology to the CPU. The chip is Socket 7 compatible, but some require modified chipsets and new motherboard designs. See Table 3.5 earlier in this chapter, which shows the Cyrix processors. The 6x86MX features 64KB of unified L1 cache and more than double the performance of the previous 6x86 CPUs. The 6x86MX is offered in clock speeds ranging from 180 to 266MHz, and like the 6x86, it is Socket 7 compatible. When running at speeds of 300MHz and higher, the 686MX was renamed the MII. Besides the higher speeds, all other functions are virtually identical. All Cyrix chips were manufactured by other companies such as IBM, which also markets the 6x86 chips under its own name. National began manufacturing Cyrix processors during 1998, but now that Cyrix is selling them off, the future is unclear. Note that later versions of the 6x86MX chip have been renamed the MII to deliberately invoke comparisons with the Pentium II, instead of the regular Pentium processor. The MII chips are not redesigned; they are, in fact, the same 6x86MX chips as before, only running at higher clock rates. The first renamed 6x86MX chip is the MII 300, which actually runs at only 233MHz on a 66MHz Socket 7 motherboard. There is also an MII 333, which will run at a 250MHz clock speed on newer 100MHz Super7 motherboards. Cyrix also has made an attempt at capturing even more of the low-end market than it already has by introducing a processor called the MediaGX. This is a low-performance cross between a 486 and a Pentium combined with a custom motherboard chipset in a two-chip package. These two chips contain everything necessary for a motherboard, except the Super I/O chip, and make very low-cost PCs possible. Expect to see the MediaGX processors on the lowest end, virtually disposable-type PCs. Later versions of these chips will include more multimedia and even network support. IDT Winchip Another offering in the chip market is from Integrated Device Technology (IDT). A longtime chip manufacturer that was better known for making SRAM (cache memory) chips, IDT acquired Centaur Technology, which had designed a chip called the C6 Winchip. Now with IDT's manufacturing capability, the C6 processor became a reality. Featuring a very simple design, the C6 Winchip is more like a 486 than a Pentium. It does not have the superscalar (multiple instruction pipelines) of a Pentium; it has a single high-speed pipeline instead. Internally, it seems the C6 has little in common with other fifth- and sixth- generation x86 processors. Even so, according to Centaur, it closely matches the performance of a Pentium MMX when running the Winstone 97 business benchmark, although that benchmark does not focus on multimedia performance. It also has a much smaller die (88 mm2) than a typical Pentium, which means it should cost significantly less to manufacture. The C6 has two large internal caches (32KB each for instructions and data) and will run at 180, 200, 225, and 240MHz. The power consumption is very low²14W maximum at 200MHz for the desktop chip, and 7.1 to 10.6W for the mobile chips.