Microprocessor Types and Specifications

Other Sixth-Generation Processors

Besides Intel, many other manufacturers are now making P6-type processors, but often with a difference. Most of them are designed to interface with P5 class motherboards and for the lower-end markets. AMD has recently offered up the Athlon and Duron processors, which are true sixth-generation designs using their own proprietary connection to the system.

This section examines the various sixth-generation processors from manufacturers other than Intel.

NexGen Nx586

NexGen was founded by Thampy Thomas who hired some of the people formerly involved with the 486 and Pentium processors at Intel. At NexGen, developers created the Nx586, a processor that was functionally the same as the Pentium but not pin compatible. As such, it was always supplied with a motherboard; in fact, it was normally soldered in. NexGen did not manufacture the chips or the motherboards they came in; for that it hired IBM Microelectronics. Later NexGen was bought by AMD, right before it was ready to introduce the Nx686, a greatly improved design done by Greg Favor, and a true competitor for the Pentium. AMD took the Nx686 design and combined it with a Pentium electrical interface to create a drop-in Pentium compatible chip called the K6, which actually outperformed the original from Intel.

The Nx586 had all the standard fifth-generation processor features, such as superscalar execution with two internal pipelines and a high performance integral L1 cache with separate code and data caches. One advantage is that the Nx586 includes separate 16KB instruction and 16KB data caches compared to 8KB each for the Pentium. These caches keep key instruction and data close to the processing engines to increase overall system performance.

The Nx586 also included branch prediction capabilities, which are one of the hallmarks of a sixth-generation processor. Branch prediction means the processor has internal functions to predict program flow to optimize the instruction execution.

The Nx586 processor also featured an RISC (Reduced Instruction Set Computer) core. A translation unit dynamically translates x86 instructions into RISC86 instructions. These RISC86 instructions were specifically designed with direct support for the x86 architecture while obeying RISC performance principles. They are thus simpler and easier to execute than the complex x86 instructions. This type of capability is another feature normally found only in P6 class processors.

The Nx586 was discontinued after the merger with AMD, which then took the design for the successor Nx686 and released it as the AMD-K6.

AMD-K6 Series

The AMD-K6 processor is a high-performance sixth-generation processor that is physically installable in a P5 (Pentium) motherboard. It was essentially designed for AMD by NexGen, and was first known as the Nx686. The NexGen version never appeared because it was purchased by AMD before the chip was due to be released. The AMD-K6 delivers performance levels somewhere between the Pentium and Pentium II processor due to its unique hybrid design. Because it is designed to install in Socket 7, which is a fifth-generation processor socket and motherboard design, it cannot perform quite as a true sixth-generation chip because the Socket 7 architecture severely limits cache and memory performance. However, with this processor, AMD is giving Intel a lot of competition in the low- to mid-range market, where the Pentium is still popular.

The K6 processor contains an industry-standard, high-performance implementation of the new multimedia instruction set (MMX), enabling a high level of multimedia performance. The K6-2 introduced an upgrade to MMX AMD calls 3DNow, which adds even more graphics and sound instructions. AMD designed the K6 processor to fit the low-cost, high-volume Socket 7 infrastructure. This enables PC manufacturers and resellers to speed time to market and deliver systems with an easy upgrade path for the future. AMD's state-of-the-art manufacturing facility in Austin, Texas (Fab 25) makes the AMD-K6 series processors. Initially it used AMD's 0.35 micron, five-metal layer process technology; newer variations use the 0.25 micron processor to increase production quantities because of reduced die size, as well as to decrease power consumption.

AMD-K6 processor technical features include

• Sixth-generation internal design, fifth-generation external interface

• Internal RISC core, translates x86 to RISC instructions

• Superscalar parallel execution units (seven)

• Dynamic execution

• Branch prediction

• Speculative execution

• Large 64KB L1 cache (32KB instruction cache plus 32KB write-back dual-ported data cache)

• Built-in floating-point unit (FPU)

• Industry-standard MMX instruction support

• System Management Mode (SMM)

• Ceramic Pin Grid Array (CPGA) Socket 7 design

• Manufactured using a 0.35 micron and 0.25 micron, five-layer design

The K6-2 adds

• Higher clock speeds

• Higher bus speeds of up to 100MHz (Super7 motherboards)

• 3DNow; 21 new graphics and sound processing instructions

The K6-3 adds

• 256KB of on-die full-core speed L2 cache

The addition of the full speed L2 cache in the K6-3 is significant. It brings the K6 series to a level where it can fully compete with the Intel Celeron and Pentium II processors. The 3DNow capability added in the K6-2/3 is also being exploited by newer graphics programs, making these processors ideal for lower-cost gaming systems.

The AMD-K6 processor architecture is fully x86 binary code compatible, which means it runs all Intel software, including MMX instructions. To make up for the lower L2 cache performance of the Socket 7 design, AMD has beefed up the internal L1 cache to 64KB total, twice the size of the Pentium II or III. This, plus the dynamic execution capability, allows the K6 to outperform the Pentium and come close to the Pentium II in performance for a given clock rate. The K6-3 is even better with the addition of full-core speed L2 cache.

Both the AMD-K5 and AMD-K6 processors are Socket 7 bus-compatible. However, certain modifications might be necessary for proper voltage setting and BIOS revisions. To ensure reliable operation of the AMD-K6 processor, the motherboard must meet specific voltage requirements.

The AMD processors have specific voltage requirements. Most older split-voltage motherboards default to 2.8v Core/3.3v I/O, which is below specification for the AMD-K6 and could cause erratic operation. To work properly, the motherboard must have Socket 7 with a dual-plane voltage regulator supplying 2.9v or 3.2v (233MHz) to the CPU core voltage (Vcc2) and 3.3v for the I/O (Vcc3). The voltage regulator must be capable of supplying up to 7.5A (9.5A for the 233MHz) to the processor. When used with a 200MHz or slower processor, the voltage regulator must maintain the core voltage within 145 mV of nominal (2.9v+/-145 mV). When used with a 233MHz processor, the voltage regulator must maintain the core voltage within 100 mV of nominal (3.2v+/-100 mV).

If the motherboard has a poorly designed voltage regulator that cannot maintain this performance, unreliable operation can result. If the CPU voltage exceeds the absolute maximum voltage range, the processor can be permanently damaged. Also note that the K6 can run hot. Ensure your heat sink is securely fitted to the processor and the thermally conductive grease or pad is properly applied.

The motherboard must have an AMD-K6 processor-ready BIOS with support for the K6 built in. Award has that support in its March 1, 1997 or later BIOS, AMI had K6 support in any of its BIOS with CPU Module 3.31 or later, and Phoenix supports the K6 in version 4.0, release 6.0, or release 5.1 with build dates of 4/7/97 or later.

Because these specifications can be fairly complicated, AMD keeps a list of motherboards that have been verified to work with the AMD-K6 processor on its Web site. All the motherboards on that list have been tested to work properly with the AMD-K6. So, unless these requirements can be verified elsewhere, it is recommended that you only use a motherboard from that list with the AMD-K6 processor.

The multiplier, bus speed, and voltage settings for the K6 are shown in Table 3.38. You can identify which AMD-K6 you have by looking at the markings on this chip, as shown in Figure 3.54.

Table 3.38 AMD-K6 Processor Speeds and Voltages

Figure 3.54 AMD-K6 processor markings.

Older motherboards achieve the 3.5x setting by setting jumpers for 1.5x. The 1.5x setting for older motherboards equates to a 3.5x setting for the AMD-K6 and newer Intel parts. To get the 4x and higher setting requires a motherboard that controls three BF (bus frequency) pins, including BF2. Older motherboards can only control two BF pins. The settings for the multipliers are shown in Table 3.39.

Table 3.39 AMD-K6 Multiplier Settings

These settings are normally controlled by jumpers on the motherboard. Consult your motherboard documentation to see where they are and how to set them for the proper multiplier and bus speed settings.

Unlike Cyrix and some of the other Intel competitors, AMD is a manufacturer and a designer. This means it designs and builds its chips in its own fabs. Like Intel, AMD is migrating to 0.25 micron process technology and beyond. The original K6 has 8.8 million transistors and is built on a 0.35 micron, five-layer process. The die is 12.7mm on each side, or about 162 square mm. The K6-3 uses a 0.25 micron process and now incorporates 21.3 million transistors on a die only 10.9mm on each side, or about 118 square mm. Further process improvements will enable even more transistors, smaller die, higher yields, and greater numbers of processors. AMD has recently won contracts with several high-end system suppliers, which gives it an edge on the other Intel competitors. AMD has delivered more than 50 million Windows-compatible CPUs in the last five years.

Because of its performance and compatibility with the Socket 7 interface, the K6 series is often looked at as an excellent processor upgrade for motherboards currently using older Pentium or Pentium MMX processors. Although they do work in Socket 7, the AMD-K6 processors have different voltage and bus speed requirements than the Intel processors. Before attempting any upgrades, you should check the board documentation or contact the manufacturer to see if your board will meet the necessary requirements. In some cases, a BIOS upgrade will also be necessary.

AMD Athlon

The Athlon is AMD's successor to the K6 series (see Figure 3.55). The Athlon is a whole new chip from the ground up and does not interface via the Socket 7 or Super7 sockets like its previous chips. In the initial Athlon versions, AMD used a cartridge design almost exactly like that of the Intel Pentium II and III. This was due to the fact that the original Athlons used 512KB of external L2 cache which was mounted on the processor cartridge board. The external cache ran at either one-half core, two-fifths core, or one-third core depending on which speed processor you had. In June of 2000 AMD introduced a revised version of the Athlon (codenamed Thunderbird) that incorporates 256KB of L2 cache directly on the processor die. This on-die cache runs at full-core speed and eliminates a bottleneck in the original Athlon systems. Along with the change to on-die L2 cache, the Athlon was also introduced in a PGA (Pin Grid Array) or chip Socket A version, which is replacing the Slot A cartridge version.

Although the Slot A cartridge looks a lot like the Intel Slot 1, and the Socket A looks like Intel's Socket 370, the pinouts are completely different and the AMD chips do not work in the same motherboards as the Intel chips. This was by design, as AMD was looking for ways to improve its chip architecture and distance itself from Intel. Special blocked pins in either socket or slot design prevent accidentally installing the chip in the wrong orientation or in the wrong slot. Figure 3.55 shows the Athlon in the Slot A cartridge. Figure 3.56 shows the Athlon in the PGA package (Socket A).

Figure 3.55 AMD Athlon processor for Slot A (cartridge form factor).

Figure 3.56 AMD Athlon processor for Socket A (PGA form factor).

The Athlon is available in speeds from 550MHz up to 1GHz and beyond and uses a 200MHz front-side bus called the EV6 to connect to the motherboard North Bridge chip as well as other processors. Licensed from Digital Equipment, the EV6 bus is the same as that used for the Alpha 21264 processor, now owned by Compaq. The EV6 bus uses a clock speed of 100MHz but double-clocks the data, transferring data twice per cycle, for a cycling speed of 200MHz. Since the bus is eight bytes (64 bits) wide, this results in a throughput of eight bytes times 200MHz or 1.6GB/sec. This is superior to the Intel processors that use a front-side bus speed of only up to 133MHz, which results in 8 bytes times 133MHz or 1.07GB/sec. bandwidth. The AMD bus design eliminates a potential bottleneck between the chipset and processor and allows for more efficient transfers compared to other processors. The use of the EV6 bus is one of the primary reasons the Athlon and Duron chips perform so well.

The Athlon has a very large 128KB of L1 cache on the processor die, and one-half, two-fifths, or one-third core speed 512KB L2 cache in the cartridge in the older versions, or 256KB of full-core speed cache in the later ones. All PGA socket A versions have the full speed cache. The Athlon also has support for MMX and the Enhanced 3DNow instructions, which are 45 new instructions designed to support graphics and sound processing. 3DNow is very similar to Intel's SSE (Streaming SIMD Extensions) in design and intent, but the specific instructions are different and require software support. Fortunately most companies producing graphics software have decided to support the 3DNow instructions along with the Intel SSE instructions, with only a few exceptions.

The initial production of the Athlon used 0.25 micron technology, with newer and faster versions being made on a 0.18 micron process. The latest versions are even built using copper metal technology, a first in the PC processor business. Eventually all other processors will follow, as copper inconnects allow for lower power consumption and faster operation.

Table 3.40 shows detailed information on the Slot-A version of the Athlon processor.

Table 3.40 AMD Athlon Slot-A Cartridge Processor Information

Table 3.41 shows information on the PGA (Pin Grid Array) or Socket A version of the AMD Athlon processor.

Table 3.41 AMD Athlon PGA (Pin Grid Array) Processor Information

AMD is taking on Intel full force in the high-end market with the Athlon. It beat Intel to the 1GHz mark by introducing its 1GHz Athlon 2 days before Intel introduced the 1GHz Pentium III, and in most benchmarks the AMD Athlon compares as equal if not superior to the Intel Pentium III.

AMD Duron

The AMD Duron processor (code-named Spitfire) was announced in June 2000 and is a derivative of the AMD Athlon processor in the same fashion as the Celeron is a derivative of the Pentium II and III (see Figure 3.57). Basically the Duron is an Athlon with less L2 cache; all other capabilities are essentially the same. It is designed to be a lower-cost version with less cache, however only slightly less performance. In keeping with the low-cost theme, Duron contains 64KB on-die L2 cache and is designed for Socket-A, a socket version of the Athlon Slot-A. With the high-value design the Duron processor is expected to compete in the sub $1,000 PC market against the Celeron, just as the Athlon is designed to compete in the higher end Pentium III market.

Since the Duron processor is derived from the Athlon core it includes the Athlon 200MHz front-side system bus (interface to the chipset) as well as enhanced 3DNow instructions.

Figure 3.57 AMD Duron processor.

Table 3.42 shows information on the PGA (Pin Grid Array) or Socket A version of the AMD Athlon processor.

Table 3.42 AMD Duron Processor Information

Cyrix MediaGX

The Cyrix MediaGX is designed for low-end sub-$1,000 retail store systems that must be highly integrated and low priced. The MediaGX integrates the sound, graphics, and memory control by putting these functions directly within the processor. With all these functions pulled "on chip," MediaGX-based PCs are priced lower than other systems with similar features.

The MediaGX processor integrates the PCI interface, coupled with audio, graphics, and memory-control functions, right into the processor unit. As such, a system with the MediaGX doesn't require a costly graphics or sound card. Not only that, but on the motherboard level, the MediaGX and its companion chip replace the processor, North and South Bridge chips, the memory control hardware, and L2 cache found on competitive Pentium boards. Finally, the simplified PC design of the MediaGX, along with its low-power and low-heat characteristics, allow the OEM PC manufacturer to design a system in a smaller form factor with a reduced power-supply requirement.

The MediaGX processor is not a Socket 7 processor; in fact, it does not go in a socket at all—it is permanently soldered into its motherboard. Because of the processor's high level of integration, motherboards supporting MediaGX processors and its companion chip (Cx5510) are of a different design than conventional Pentium boards. As such, a system with the MediaGX processor is more of a disposable system than an upgradable system. You will not be able to easily upgrade most components in the system, but that is often not important in the very low-end market. If upgradability is important, look elsewhere. On the other hand, if you need the lowest-priced system possible, one with the MediaGX might fill the bill.

The MediaGX is fully Windows-compatible and will run the same software as an equivalent Pentium. You can expect a MediaGX system to provide equivalent performance as a given Pentium system at the same megahertz. The difference with the MediaGX is that this performance level is achieved at a much lower cost. Because the MediaGX processor is soldered into the motherboard and requires a custom chipset, it is only sold in a complete motherboard form.

There is also an improved MMX-enhanced MediaGX processor that features MPEG1 support, Microsoft PC97 compliance for Plug-and-Play access, integrated game port control, and AC97 audio compliance. It supports Windows 95 and DOS-based games, and MMX software as well. Such systems will also include two universal serial bus (USB) ports, which will accommodate the new generation of USB peripherals such as printers, scanners, joysticks, cameras, and more.

The MediaGX processor is offered at 166 and 180MHz, while the MMX-enhanced MediaGX processor is available at 200MHz and 233MHz. Compaq is using the MMX-enhanced MediaGX processor in its Presario 1220 notebook PCs, which is a major contract win for Cyrix. Other retailers and resellers are offering low-end, low-cost systems in retail stores nationwide.

Cyrix/IBM 6x86 (M1) and 6x86MX (MII)

The Cyrix 6x86 processor family consists of the now-discontinued 6x86 and the newer 6x86MX processors. They are similar to the AMD-K5 and K6 in that they offer sixth-generation internal designs in a fifth-generation P5 Pentium compatible Socket 7 exterior.

The Cyrix 6x86 and 6x86MX (renamed MII) processors incorporate two optimized superpipelined integer units and an on-chip floating-point unit. These processors include the dynamic execution capability that is the hallmark of a sixth-generation CPU design. This includes branch prediction and speculative execution.

The 6x86MX/MII processor is compatible with MMX technology to run the latest MMX games and multimedia software. With its enhanced memory-management unit, a 64KB internal cache, and other advanced architectural features, the 6x86MX processor achieves higher performance and offers better value than competitive processors.

Features and benefits of the 6x86 processors include

• Superscalar architecture. Two pipelines to execute multiple instructions in parallel.

• Branch prediction. Predicts with high accuracy the next instructions needed.

• Speculative execution. Allows the pipelines to continuously execute instructions following a branch without stalling the pipelines.

• Out-of-order completion. Lets the faster instruction exit the pipeline out of order, saving processing time without disrupting program flow.

The 6x86 incorporates two caches: a 16KB dual-ported unified cache and a 256-byte instruction line cache. The unified cache is supplemented with a small quarter-K sized high-speed, fully associative instruction line cache. The improved 6x86MX design quadruples the internal cache size to 64KB, which significantly improves performance.

The 6x86MX also includes the 57 MMX instructions that speed up the processing of certain computing-intensive loops found in multimedia and communication applications.

All 6x86 processors feature support for System Management Mode (SMM). This provides an interrupt that can be used for system power management or software transparent emulation of I/O peripherals. Additionally, the 6x86 supports a hardware interface that allows the CPU to be placed into a low-power suspend mode.

The 6x86 is compatible with x86 software and all popular x86 operating systems, including Windows 95/98/Me, Windows NT/2000, OS/2, DOS, Solaris, and UNIX. Additionally, the 6x86 processor has been certified Windows 95 compatible by Microsoft.

As with the AMD-K6, there are some unique motherboard requirements for the 6x86 processors. Cyrix maintains a list of recommended motherboards on its Web site that should be consulted if you are considering installing one of these chips in a board.

When installing or configuring a system with the 6x86 processors, you have to set the correct motherboard bus speed and multiplier settings. The Cyrix processors are numbered based on a P-rating scale, which is not the same as the true megahertz clock speed of the processor.

See "Cyrix P-Ratings" earlier in this chapter to see the correct and true speed settings for the Cyrix 6x86 processors.

Note that because of the use of the P-rating system, the actual speed of the chip is not the same number at which it is advertised. For example, the 6x86MX-PR300 is not a 300MHz chip; it actually runs at only 263MHz or 266MHz, depending on exactly how the motherboard bus speed and CPU clock multipliers are set. Cyrix says it runs as fast as a 300MHz Pentium, hence the P-rating. Personally, I wish it would label the chips at the correct speed and then say that it runs faster than a Pentium at the same speed.

To install the 6x86 processors in a motherboard, you also have to set the correct voltage. Normally, the markings on top of the chip indicate which voltage setting is appropriate. Various versions of the 6x86 run at 3.52v (use VRE setting), 3.3v (VR setting), or 2.8v (MMX) settings. The MMX versions use the standard split-plane 2.8v core 3.3v I/O settings.