Home > Articles > Hardware

Intel-Compatible Processors (AMD and Cyrix)

Several companies—mainly AMD and Cyrix—have 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-Rating

Actual CPU Speed (MHz)

Clock Multiplier

Motherboard Speed (MHz)

CPU Socket or Slot

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

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 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 low—14W maximum at 200MHz for the desktop chip, and 7.1 to 10.6W for the mobile chips. This processor will likely have some success in the low-end market.

P-Ratings

To make it easier to understand processor performance, the P-Rating system was jointly developed by Cyrix, IBM Microelectronics, SGS-Thomson Microelectronics, and Advanced Micro Devices. This new rating, titled the (Performance) P-Rating, equates delivered performance of microprocessor to that of an Intel Pentium. To determine a specific P-Rating, Cyrix and AMD use benchmarks such as Winstone 9x. Winstone 9x is a widely used, industry-standard benchmark that runs a number of Windows-based software applications.

The idea is fine, but in some cases it can be misleading. A single benchmark or even a group of benchmarks cannot tell the whole story on system or processor performance. In most cases, the companies selling PR-rated processors have people believing that they are really running at the speed indicated on the chip. For example, a Cyrix/IBM 6x86MX-PR200 does not really run at 200MHz; instead, it runs at 166MHz. I guess the idea is that it "feels" like 200MHz or compares to some Intel processor running at 200MHz (which one?). I am not in favor of the P-Rating system and prefer to just report the processor's true speed in MHz. If it happens to be 166 but runs faster than most other 166 processors, so be it—but I don't like to number it based on some comparison like that.

NOTE

See "Cyrix P-Ratings" and "AMD P-Ratings" earlier in this chapter to see how P-Ratings stack up against the actual processor speed in MHz.

The Ziff-Davis Winstone benchmark is used because it is a real-world, application-based benchmark that contains the most popular software applications (based on market share) that run on a Pentium processor. Winstone also is a widely used benchmark and is freely distributed and available.

  • + Share This
  • 🔖 Save To Your Account

Related Resources

There are currently no related titles. Please check back later.