Upgrading and Repairing PCs (17th Edition)

The P6 (686) processors represent a new generation with features not found in the previous generation units. The P6 processor family began when the Pentium Pro was released in November 1995. Since then, Intel has released many other P6 chips, all using the same basic P6 core processor as the Pentium Pro. Table 3.28 shows the variations in the P6 family of processors.

The main new feature in the fifth-generation Pentium processors was the superscalar architecture, in which two instruction execution units could execute instructions simultaneously in parallel. Later fifth-generation chips also added MMX technology to the mix, as well. So then what did Intel add in the sixth generation to justify calling it a whole new generation of chip? Besides many minor improvements, the real key features of all sixth-generation processors are Dynamic Execution and the Dual Independent Bus (DIB) architecture, plus a greatly improved superscalar design.

Dynamic Execution

Dynamic execution enables the processor to execute more instructions on parallel, so tasks are completed more quickly. This technology innovation is comprised of three main elements:

• Multiple branch prediction. Predict the flow of the program through several branches

• Dataflow analysis. Schedules instructions to be executed when ready, independent of their order in the original program

• Speculative execution. Increases the rate of execution by looking ahead of the program counter and executing instructions that are likely to be necessary

Dual Independent Bus

The other main P6 architecture feature is known as the Dual Independent Bus. This refers to the fact that the processor has two data buses: one for the system (motherboard) and the other just for cache. This enables the cache memory to run at speeds previously not possible.

Other Sixth-Generation Improvements

Finally, the P6 architecture upgrades the superscalar architecture of the P5 processors by adding more instruction execution units and by breaking down the instructions into special micro-ops. This is where the CISC instructions are broken down into more RISC commands. The RISC-level commands are smaller and easier for the parallel instruction units to execute more efficiently. With this design, Intel has brought the benefits of a RISC processorhigh-speed dedicated instruction executionto the CISC world. Note that the P5 had only two instruction units, whereas the P6 has at least six separate dedicated instruction units. It is said to be three-way superscalar because the multiple instruction units can execute up to three instructions in one cycle.

Other improvements in efficiency also are included in the P6 architecture: built-in multiprocessor support, enhanced error detection and correction circuitry, and optimization for 32-bit software.

Rather than just being a faster Pentium, the Pentium Pro, Pentium II/III, and other sixth-generation processors have many feature and architectural improvements. The core of the chip is very RISC-like, whereas the external instruction interface is classic Intel CISC. By breaking down the CISC instructions into several RISC instructions and running them down parallel execution pipelines, the overall performance is increased.

Compared to a Pentium at the same clock speed, the P6 processors are fasteras long as you're running 32-bit software. The P6 Dynamic Execution is optimized for performance primarily when running 32-bit software, such as Windows NT. If you are using 16-bit software, such as Windows 95 or 98 (which still operate part time in a 16-bit environment) and most older applications, the P6 does not provide as marked a performance improvement over similarly speed-rated Pentium and Pentium-MMX processors. That's because the Dynamic Execution capability is not fully exploited. Because of this, Windows NT/2000/XP often are regarded as the most desirable operating systems for use with Pentium Pro/II/III/Celeron processors. Although this is not exactly true (a Pentium Pro/II/III/Celeron runs fine under Windows 95/98), Windows NT/2000/XP does take better advantage of the P6's capabilities.

Note that it is really not so much the operating system but which applications you use. Software developers can take steps to gain the full advantages of the sixth-generation processors. This includes using modern compilers that can improve performance for all current Intel processors, writing 32-bit code where possible, and making code as predictable as possible to take advantage of the processor's Dynamic Execution multiple branch prediction capabilities.

Pentium Pro Processors

Intel's successor to the Pentium is called the Pentium Pro. The Pentium Pro was the first chip in the P6 or sixth-generation processor family. It was introduced in November 1995 and became widely available in 1996. The chip is a 387-pin unit that resides in Socket 8, so it is not pin compatible with earlier Pentiums. The chip is unique among processors because it is constructed in a multichip module (MCM) physical format, which Intel calls a dual cavity PGA package. Inside the 387-pin chip carrier are two dies. One contains the actual Pentium Pro processor (shown in Figure 3.41), and the other contains a 256KB (the Pentium Pro with 256KB cache is shown in Figure 3.42), 512KB, or 1MB L2 cache. The processor die contains 5.5 million transistors, the 256KB cache die contains 15.5 million transistors, and the 512KB cache die(s) have 31 million transistors eachfor a potential total of nearly 68 million transistors in a Pentium Pro with 1MB of internal cache! A Pentium Pro with 1MB cache has two 512KB cache die and a standard P6 processor die (see Figure 3.43).

The main processor die includes a 16KB split L1 cache with an 8KB two-way set associative cache for primary instructions and an 8KB four-way set associative cache for data.

Another sixth-generation processor feature found in the Pentium Pro is the DIB architecture, which addresses the memory bandwidth limitations of previous-generation processor architectures. Two buses make up the DIB architecture: the L2 cache bus (contained entirely within the processor package) and the processor-to-main memory system bus. The speed of the dedicated L2 cache bus on the Pentium Pro is equal to the full-core speed of the processor. This was accomplished by embedding the cache chips directly into the Pentium Pro package. The DIB processor bus architecture addresses processor-to-memory bus bandwidth limitations. It offers up to three times the performance bandwidth of the single-bus, "Socket 7" generation processors, such as the Pentium.

Table 3.29 shows Pentium Pro processor specifications, and Table 3.30 shows the specifications for each model within the Pentium Pro family because many variations exist from model to model.

Performance comparisons on the iCOMP 2.0 Index rate a classic Pentium 200MHz at 142, whereas a Pentium Pro 200MHz scores 220. Just for comparison, note that a Pentium MMX 200MHz falls right about in the middle in regards to performance at 182. Keep in mind that using a Pentium Pro with any 16-bit software applications nullifies much of the performance gain shown by the iCOMP 2.0 rating.

Similar to the Pentium before it, the Pentium Pro runs clock multiplied on a 66MHz motherboard. The following table lists speeds for Pentium Pro processors and motherboards:

The integrated L2 cache is one of the really outstanding features of the Pentium Pro. By building the L2 cache into the CPU and getting it off the motherboard, the Pentium Pro can now run the cache at full processor speed rather than the slower 60MHz or 66MHz motherboard bus speed. In fact, the L2 cache features its own internal 64-bit back-side bus, which does not share time with the external 64-bit front-side bus used by the CPU. The internal registers and data paths are still 32-bit, as with the Pentium. By building the L2 cache into the system, motherboards can be cheaper because they no longer require separate cache memory. Some boards might still try to include cache memory in their designs, but the general consensus is that L3 cache (as it would be called) would offer less improvement with the Pentium Pro than with the Pentium. The incorporation of L2 cache is one of the most enduring legacies of the Pentium Pro because this feature has been incorporated into virtually every Intel and AMD processor built since, with the notable exception of the original Celeron.

One of the features of the built-in L2 cache is that multiprocessing is greatly improved. Rather than just SMP, as with the Pentium, the Pentium Pro supports a type of multiprocessor configuration called the Multiprocessor Specification (MPS 1.1). The Pentium Pro with MPS enables configurations of up to four processors running together. Unlike other multiprocessor configurations, the Pentium Pro avoids cache coherency problems because each chip maintains a separate L1 and L2 cache internally.

Pentium Probased motherboards were pretty much exclusively PCI and ISA bus-based, and Intel has produced its own chipsets for these motherboards. Because of the greater cooling and space requirements, Intel designed the new ATX motherboard form factor to better support the Pentium Pro and other future processors, such as the Pentium II/III/4. However, systems using the Pentium Pro use various types of motherboard form factors, including ATX, Baby-AT, and proprietary models.

Four special VID pins are on the Pentium Pro processor. These pins can be used to support automatic selection of power supply voltage. Therefore, a Pentium Pro motherboard does not have voltage regulator jumper settings like most Pentium boards, which greatly eases the setup and integration of a Pentium Pro system. These pins are not actually signals, but are either an open circuit in the package or a short circuit to voltage. The sequence of opens and shorts defines the voltage the processor requires. In addition to allowing for automatic voltage settings, this feature was designed to support voltage specification variations on future Pentium Pro processors. The VID pins are named VID0 through VID3, and the definition of these pins is shown in Table 3.31. A 1 in this table refers to an open pin, and a 0 refers to a short to ground. The voltage regulators on the motherboard should supply the requested voltage or disable itself.

Most Pentium Pro processors run at 3.3V, but a few run at 3.1V. Note that the 1111 (or all opens) ID can be used to detect the absence of a processor in a given socket.

The Pentium Pro never did become very popular on the desktop, but it did find a niche in file-server applications primarily because of the full-core speed high-capacity internal L2 cache. For a time, Intel offered an OverDrive upgrade processor for the Pentium Pro, but it no longer offers any OverDrive processors. At one time, PowerLeap offered several upgrades for Pentium Pro that used 533MHz700MHz-class Celeron PPGA processors in an adapter, but these products are no longer available.

Pentium II Processors

Intel revealed the Pentium II in May 1997. Prior to its official unveiling, the Pentium II processor was popularly referred to by its codename, Klamath, and was surrounded by much speculation throughout the industry. The Pentium II is essentially the same sixth-generation processor as the Pentium Pro, with MMX technology added (which included double the L1 cache and 57 new MMX instructions); however, there are a few twists to the design. The Pentium II processor die is shown in Figure 3.44.

From a physical standpoint, it was a big departure from previous processors. Abandoning the chip in a socket approach used by virtually all processors up until this point, the Pentium II chip is characterized by its SEC cartridge design. The processor, along with several L2 cache chips, is mounted on a small circuit board (much like an oversized-memory SIMM) as shown in Figure 3.45, and the circuit board is then sealed in a metal and plastic cartridge. The cartridge is then plugged into the motherboard through an edge connector called Slot 1, which looks very much like an adapter card slot.

The two variations on these cartridges are called SECC (single edge contact cartridge) and SECC2. Figure 3.46 shows a diagram of the SECC package; Figure 3.47 shows the SECC2 package.

As you can see from these figures, the SECC2 version was cheaper to make because it uses fewer overall parts. It also allowed for a more direct heatsink attachment to the processor for better cooling. Intel transitioned from SECC to SECC2 in the beginning of 1999; all later PII chips, and the Slot 1 PIII chips that followed, use the improved SECC2 design.

By using separate chips mounted on a circuit board, Intel could build the Pentium II much less expensively than the multiple die within a package used in the Pentium Pro. Intel could also use cache chips from other manufacturers and more easily vary the amount of cache in future processors compared to the Pentium Pro design.

Intel offered Pentium II processors with the following speeds:

The Pentium II processor core has 7.5 million transistors and is based on Intel's advanced P6 architecture. The Pentium II started out using a 0.35-micron process technology, although the 333MHz and faster Pentium IIs are based on 0.25-micron technology. This enables a smaller die, allowing increased core frequencies and reduced power consumption. At 333MHz, the Pentium II processor delivers a 75%150% performance boost, compared to the 233MHz Pentium processor with MMX technology, and approximately 50% more performance on multimedia benchmarks. As shown earlier in Table 3.8, the iCOMP 2.0 Index rating for the Pentium II 266MHz chip is more than twice as fast as a classic Pentium 200MHz.

Aside from speed, the best way to think of the Pentium II is as a Pentium Pro with MMX technology instructions and a slightly modified cache design. It has the same multiprocessor scalability as the Pentium Pro, as well as the integrated L2 cache. The 57 new multimedia-related instructions carried over from the MMX processors and the capability to process repetitive loop commands more efficiently are included as well. Also included as a part of the MMX upgrade is double the internal L1 cache from the Pentium Pro (from 16KB total to 32KB total in the Pentium II).

Maximum power usage for the Pentium II is shown in the following table:

You can see that the highest speed 450MHz version of the Pentium II actually uses less power than the slowest original 233MHz version! This was accomplished by using the smaller 0.25-micron process and running the processor on a lower voltage of only 2.0V. Pentium III and subsequent processors used even smaller processes and lower voltages to continue this trend.

The Pentium II includes Dynamic Execution, which describes unique performance-enhancing developments by Intel and was first introduced in the Pentium Pro processor. Major features of Dynamic Execution include multiple branch prediction, which speeds execution by predicting the flow of the program through several branches; dataflow analysis, which analyzes and modifies the program order to execute instructions when ready; and speculative execution, which looks ahead of the program counter and executes instruction that are likely to be needed. The Pentium II processor expands on these capabilities in sophisticated and powerful new ways to deliver even greater performance gains.

Similar to the Pentium Pro, the Pentium II also includes DIB architecture. The term Dual Independent Bus comes from the existence of two independent buses on the Pentium II processorthe L2 cache bus and the processortomain-memory system bus. The Pentium II processor can use both buses simultaneously, thus getting as much as twice as much data in and out of the Pentium II processor as a single-bus architecture processor. The DIB architecture enables the L2 cache of the 333MHz Pentium II processor to run 2 1/2 times as fast as the L2 cache of Pentium processors. As the frequency of future Pentium II processors increases, so will the speed of the L2 cache. Also, the pipelined system bus enables simultaneous parallel transactions instead of singular sequential transactions. Together, these DIB architecture improvements offer up to three times the bandwidth performance over a single-bus architecture as with the regular Pentium.

Table 3.32 shows the general Pentium II processor specifications. Table 3.33 shows the specifications that vary by model.

The L1 cache always runs at full-core speeds because it is mounted directly on the processor die. The L2 cache in the Pentium II normally runs at half-core speed, which saves money and allows for less expensive cache chips to be used. For example, in a 333MHz Pentium II, the L1 cache runs at a full 333MHz, whereas the L2 cache runs at 167MHz. Even though the L2 cache is not at full-core speed as it was with the Pentium Pro, this is still far superior to having cache memory on the motherboard running at the 66MHz motherboard speed of most Socket 7 Pentium designs. Intel claims that the DIB architecture in the Pentium II enables up to three times the bandwidth of normal single-bus processors, such as the original Pentium.

By removing the cache from the processor's internal package and using external chips mounted on a substrate and encased in the cartridge design, Intel could use more cost-effective cache chips and more easily scale the processor up to higher speeds. The Pentium Pro was limited in speed to 200MHz, largely due to the inability to find affordable cache memory that ran any faster. By running the cache memory at half-core speed, the Pentium II can run up to 400MHz while still using 200MHz-rated cache chips. To offset the half-core speed cache used in the Pentium II, Intel doubled the basic amount of integrated L2 cache from 256KB standard in the Pro to 512KB standard in the Pentium II.

Note that the tag RAM included in the L2 cache enables up to 512MB of main memory to be cacheable in PII processors from 233MHz to 333MHz. The 350MHz, 400MHz, and faster versions include an enhanced tag-RAM that allows up to 4GB of main memory to be cacheable. If you support systems based on the Pentium II, be aware of the caching limitations in the slower processors before upgrading memory above 512MB. Uncached memory will slow down any system.

The system bus of the Pentium II provides "glueless" support for up to two processors. This enables lowcost, two-way multiprocessing on the L2 cache bus. These system buses are designed especially for servers or other mission-critical system use where reliability and data integrity are important. All Pentium IIs also include parity-protected address/request and response system bus signals with a retry mechanism for high data integrity and reliability. As a result, the Pentium II was used in many servers and workstations.

To install the Pentium II in a system, a special processor-retention mechanism is required. This consists of a mechanical support that attaches to the motherboard and secures the Pentium II processor in Slot 1 to prevent shock and vibration damage. Retention mechanisms should be provided by the motherboard manufacturer. (For example, the Intel Boxed AL440FX and DK440LX motherboards included a retention mechanism, plus other important system integration components.) The retention mechanism sometimes folds out of the way for easier storage of the motherboard component, or it might use a rigid design.

The Pentium II can generate a significant amount of heat that must be dissipated. This is accomplished by installing a heatsink on the processor. Many of the Pentium II processors use an active heatsink that incorporates a fan. Unlike heatsink fans for previous Intel boxed processors, the Pentium II fans draw power from a three-pin power header on the motherboard. Most motherboards provide several fan connectors to supply this power.

Special heatsink supports are necessary to furnish mechanical support between the fan heatsink and support holes on the motherboard. Normally, a plastic support is inserted into the heatsink holes in the motherboard next to the CPU, before installing the CPU/heatsink package. Most fan heatsinks have two components: a fan in a plastic shroud and a metal heatsink. The heatsink is attached to the processor's thermal plate and should not be removed. The fan can be removed and replaced if necessaryfor example, if it has failed. Figure 3.48 shows the SEC assembly with fan, power connectors, mechanical supports, and the slot and support holes on the motherboard.

The following tables show the specifications unique to certain versions of the Pentium II processor.

To identify exactly which Pentium II processor you have and what its capabilities are, look at the specification number printed on the SEC cartridge. You will find the specification number in the dynamic mark area on the top of the processor module. See Figure 3.49 to locate these markings.

After you have located the specification number (actually, it is an alphanumeric code), you can look it up in Table 3.34 to see exactly which processor you have.

For example, a specification number of SL2KA identifies the processor as a Pentium II 333MHz running on a 66MHz system bus, with an ECC L2 cache, and indicates that this processor runs on only 2.0V. The stepping is also identified, and by looking in the "Pentium II Specification Update Manual" published by Intel, you could figure out exactly which bugs were fixed in that revision.

The two variations of the SECC2 cartridge vary by the type of processor core package on the board. The plastic land grid array (PLGA) is the older type of packaging used in previous SECC cartridges and was eventually phased out. A newer organic land grid array (OLGA), which is a processor core package that is smaller and easier to manufacture, took its place. It also enabled better thermal transfer between the processor die and the heatsink, which was attached directly to the top of the OLGA chip package. Figure 3.50 shows the open back side (where the heatsink would be attached) of SECC2 processors with PLGA and OLGA cores.

Pentium II motherboards have an onboard voltage regulator circuit designed to power the CPU. Some Pentium II processors run at several different voltages, so the regulator must be set to supply the correct voltage for the specific processor you are installing. As with the Pentium Pro and unlike the older Pentium, no jumpers or switches must be set; the voltage setting is handled completely automatically through the VID pins on the processor cartridge. Table 3.35 shows the relationship between the pins and the selected voltage.

To ensure the system is ready for all Pentium II processor variations, the values in bold must be supported. Most Pentium II processors run at 2.8V, with some newer ones at 2.0V.

The Pentium II Mobile Module is a Pentium II for notebooks that includes the North Bridge of the high-performance 440BX chipset. This was the first chipset on the market that allowed 100MHz processor bus operation, although that feature was not supported in the mobile versions. The 440BX chipset was released at the same time as the 350MHz and 400MHz versions of the Pentium II.

Newer variations on the Pentium II include the Pentium IIPE, which is a mobile version that includes 256KB of L2 cache directly integrated into the die. Therefore, it runs at full-core speed, making it faster than the desktop Pentium II because the desktop chips use half-speed L2 cache.

Celeron

The Celeron processor is a chameleon. It was originally a P6 with the same processor core as the Pentium II in the original two versions; later it came with the same core as the PIII; and more recently it has been based on the various the Pentium 4 cores, including Prescott. It is designed mainly for lower-cost PCs.

Most of the features for the Celeron are the same as the Pentium II, III, or 4 because it uses the same internal processor cores. The main differences are in packaging, L2 cache amount, and CPU bus speed.

The first version of the Celeron was available in a package called the single edge processor package (SEPP or SEP package). The SEP package is basically the same Slot 1 design as the SECC used in the Pentium II/III, with the exception of the fancy plastic cartridge cover. This cover was deleted in the Celeron, making it cheaper to produce and sell. Essentially, the original Celeron used the same circuit board as is inside the Pentium II package.

Even without the plastic covers, the Slot 1 packaging was more expensive than it should have been. This was largely due to the processor retention mechanisms (stands) required to secure the processor into Slot 1 on the motherboard, as well as the larger and more complicated heatsinks required. This, plus competition from the lower-end Socket 7 systems using primarily AMD processors, led Intel to introduce the Celeron in a socketed form. The socket is called PGA-370 or Socket 370 because it has 370 pins. The processor package designed for this socket is called the plastic pin grid array (PPGA) package (see Figure 3.51) or flip chip PGA (FC-PGA). Both the PPGA and FC-PGA packages plug into the 370 pin socket and allow for lower-cost, lower-profile, and smaller systems because of the less expensive processor retention and cooling requirements of the socketed processor.

All Celeron processors at 433MHz and lower were available in the SEPP that plugs into the 242-contact slot connector (Slot 1). The 300MHz and higher versions were also made in the PPGA package. This means that the 300MHz to 433MHz have been available in both packages, whereas the 466MHz and higher-speed versions are available only in the PPGA. The fastest Celeron processor for Socket 370 runs at 1.4GHz; faster Celerons use Socket 478 and are based on the Pentium 4 design.

Motherboards that include Socket 370 can accept the PGA versions of both the Celeron and Pentium III in most cases. If you want to use a Socket 370 version of the Celeron in a Slot 1 motherboard, slot-to-socket adapters (usually called slot-kets) are available for about $10$20 that plug into Slot 1 and incorporate a Socket 370 on the card. Figure 3.52 shows a typical slot-ket adapter.

Highlights of the Celeron include the following:

• Available at 300MHz (300A) and higher core frequencies with 128KB on-die L2 cache; 300MHz and 266MHz core frequencies without L2 cache

• L2 cache supports up to 4GB RAM address range and ECC

• Uses same P6 core processor as the Pentium II (266MHz through 533MHz), the Pentium III (533A MHz and higher), and the Pentium 4 (1.7GHz and higher)

• Dynamic execution microarchitecture

• Operates on a 66MHz, 100MHz, 400MHz, or 533MHz CPU bus depending on the version

• Specifically designed for lower-cost value PC systems

• Includes MMX technology; Celeron 533A and higher include SSE; Celeron 1.7GHz and higher include SSE2; Celeron D models include SSE3

• More cost-effective packaging technology, including SEP, PPGA, and FC-PGA or FC-PGA2 packages

• Integrated L1 and L2 cache on most models, with amount and type depending on the version; typically, the Celeron has half the L2 cache of the processor core it is patterned after

• Integrated thermal diode for temperature monitoring

The Intel Celeron processors from the 300A and higher include integrated 128KB L2 cache. The core for the 300A through 533MHz versions that are based on the Pentium II core include 19 million transistors because of the addition of the integrated 128KB L2 cache. The 533A and faster versions are based on the Pentium III core and incorporate 28.1 million transistors. The 1.7GHz and faster versions are based on the Pentium 4 core with 42 million transistors. The Pentium III and Pentium 4based versions actually have 256KB of L2 cache on the die; however, 128KB is disabled, leaving 128KB of functional L2 cache. This was done because it was cheaper for Intel to simply make the Celeron using the same die as the Pentium III or 4 and just disable part of the cache on the Celeron versions, rather than coming up with a unique die for the newer Celerons. The Pentium IIIbased Celeron processors also support the SSE in addition to MMX instructions, whereas the Pentium 4based versions support SSE2 instructions. The older Celerons based on the Pentium II core support only MMX.

All the Celerons in SEPP and PPGA form are manufactured using the 0.25-micron process, whereas those in FC-PGA and FC-PGA2 form are made using the better 0.18-micron and 0.13-micron processes. The smaller process reduces processor heat and enables higher speeds.

The latest Celeron processors for desktop computers use the Celeron D brand name, whereas the Celeron M brand name identifies Celeron-class processors designed for use in low-cost portable computers. Celeron D processors are manufactured using the 0.09-micron process.

A Brief Celeron History

The original Celerons were economy versions of the Intel Pentium II processor. Intel figured that by taking a Pentium II and deleting the separate L2 cache chips mounted inside the processor cartridge (and also deleting the cosmetic cover), it could create a "new" processor that was basically just a slower version of the Pentium II. As such, the first 266MHz and 300MHz Celeron models didn't include any L2 cache. Unfortunately, this proved to have far too great a crippling effect on performance, so starting with the 300A versions, the Celeron received 128KB of on-die full-speed L2 cache, which was actually faster and more advanced than the 512KB of half-speed cache used in the Pentium II it was based on! In fact, the Celeron was the first PC processor to receive on-die L2 cache. It wasn't until the Coppermine version of the Pentium III appeared that on-die L2 cache migrated to Intel's main processors.

Needless to say, this caused a lot of confusion in the marketplace about the Celeron. Considering that the Celeron started out as a "crippled" Pentium II and then was revised so as to actually be superior in some ways to the Pentium II on which it was based (all the while selling for less), many didn't know just where the Celeron stood in terms of performance. Fortunately, the crippling lack of L2 cache existed only in the earliest Celeron versions; all of those at speeds greater than 300MHz have on-die full-speed L2 cache.

The earliest Celerons from 266MHz up through 400MHz were produced in a SEPP design that physically looked like a circuit board and that was designed to fit into Slot 1. This is the same slot the Pentium II used, meaning the Celeron SEPP plugged into any Pentium II Slot-1 motherboard. As the Celeron continued to develop, the form factor was changed to correspond with changes in the Pentium II-, III-, and 4-class processors from which it was adapted. Starting with the 300A processor (300MHz Celeron with 128KB of on-die Level 2 cache), Celerons were produced in a PPGA package using the Socket 370 interface. This socket, with differences in voltage, was later used for most versions of the Pentium III. Celerons using Socket 370 range in speed from 300MHz all the way up to 1.4GHz. Along the way, the packaging changed from PPGA to FC-PGA and FC-PGA2. The latter added a metal heat spreader on top of the die offering better protection for the fragile die.

Celeron processors based on the Pentium 4 are produced in one of two package designs. Some use the FC-PGA2 package that fits into the same Socket 478 used by most Pentium 4 processors. However, the Celeron D is available in both the Socket 478 package and Socket T (LGA775) package used by the Prescott core version of the Pentium 4. The Celeron was never produced in the short-lived Socket 423 form factor the original Pentium 4 processors used.

As this very brief history shows, the name Celeron has never meant anything more specific than a reduced-performance version of Intel's current mainstream processor. Before you can decide whether a particular Celeron processor is a suitable choice, you need to know what its features are and especially on which processor it is based. At least eight discrete variations of the Celeron processor exist, which are detailed in Table 3.36.

^[1] All Celeron III below 800MHz use the 66MHz CPU bus; all Celeron III from 800MHz through 1.1GHz use the 100MHz bus.

^[2] Some Socket T processors support EM64T (64-bit extensions) and Execute Disable Bit antivirus protection. See Table 3.37 for details.

Figure 3.53 shows most of the various Celeron package types.

As you can see, there is a wide range of what is called a Celeron, and you could consider the Celeron as a family of different core processor models in several package variations.

The following sections discuss the differences between these Celeron processors.

Socket 370 Celerons

Socket 370 Celerons are based on various versions of the Pentium II and Pentium III architecture.

Intel offered Celeron IIIA versions for Socket 370 motherboards in speeds from 900MHz to 1.4GHz. These processors have a CPU bus speed of 100MHz. Celeron IIIA versions based on the Pentium III Tualatin core have 256KB of L2 cache, whereas those based on the earlier Pentium III Coppermine core or Pentium II Deschutes core have 128KB of L2 cache. Compared to Celerons based on the previous Pentium III Coppermine core, Tualatin-based Celerons have the following differences:

• Larger L2 memory cache (256KB versus 128KB)

• Improved L2 cache design for better performance

• FC-PGA2 packaging, which includes a metal heat spreader over the fragile CPU core to protect it when attaching a heatsink

Like the Tualatin-core versions of the Pentium III, Celerons based on the Tualatin core don't work in motherboards designed for older Pentium III or Celeron chips. Socket 370 is physically the same, but the Tualatin core redefines 10 pins in the socket, which requires corresponding changes in the chipset and motherboard. So, if you're looking for a way to speed up an older Celeron by installing a Tualatin-core Celeron IIIA, make sure the motherboard is Tualatin-ready. Also note that Tualatin-core Celerons use the FC-PGA2 packaging, which includes a heat spreader on top of the CPU die. This requires a compatible heatsink.

Socket 478 Celeron and Celeron D Processors

Celeron processors in Socket 478 fall into three distinct camps, as Table 3.36 previously demonstrated:

• Celerons running at 1.7GHz and 1.8GHz are based on the original Pentium 4 Willamette core and have a 400MHz CPU bus, 128KB of L2 cache, and SSE2 support.

• Celerons running at 2GHz2.8GHz with a 400MHz CPU bus are based on the Pentium 4 Northwood core, have 128KB of L2 cache, and have SSE2 support.

• Celeron D processors are based on the Prescott core used by the latest Pentium 4 processors; range in speed from 2.13GHz to 3.2GHz; and feature a 533MHz CPU bus, 256KB of L2 cache, and SSE3 support.

Socket T (LGA 775) Celeron D Processors

Celeron D processors in Socket T (LGA 775) range in speed from 2.53GHz to 3.2GHz and feature a 533MHz CPU bus, 256KB of L2 cache, and SSE3 support just like their Socket 478 Celeron D siblings. However, they also have two unique features compared to Celeron D processors in Socket 478:

• All-feature support for the Execute Disable Bit feature, which helps block buffer overrun virus attacks, when used with a compatible operating system such as Windows XP Service Pack 2.

• Some also feature support for EM64T, Intel's implementation of 64-bit extensions to the IA32 processor architecture. Thus, Celeron D processors with EM64T provide a low-cost way to use 64-bit operating systems such as Windows XP Professional x64 Edition or 64-bit Linux distributions.

Celeron D processors use the Intel processor numbering scheme introduced in 2004. Use Table 3.37 to determine the specific features supported by a particular Celeron D processor model number.

Because Intel has offered Celeron and Celeron D processors in many distinctive variations, it's easy to get confused as to which is which, or which is available at a specific speed. By reading the spec number off a particular chip and looking up the number on the Intel developer website (developer.intel. com) or by using the reference charts in this book, you can find out the exact specification including socket type, voltage, stepping, cache size, and other information about the chip.

Pentium III

The Pentium III processor, shown in Figure 3.54, was first released in February 1999 and introduced several new features to the P6 family. It is essentially the same core as a Pentium II with the addition of SSE instructions and integrated on-die L2 cache in the later versions. SSE consists of 70 new instructions that dramatically enhance the performance and possibilities of advanced imaging, 3D, streaming audio, video, and speech-recognition applications.

Originally based on Intel's advanced 0.25-micron CMOS process technology, the PIII core started out with more than 9.5 million transistors. In late 1999, Intel shifted to a 0.18-micron process die (codenamed Coppermine) and added 256KB of on-die L2 cache, which brought the transistor count to 28.1 million. The latest version of the Pentium III (codenamed Tualatin) uses a 0.13-micron process and has 44 million transistors; motherboards made before the Tualatin-core versions of the Pentium III generally do not support this processor because of logical pinout changes. The Pentium III was manufactured in speeds from 450MHz through 1.4GHz, as well as in server versions with larger or faster cache known as the Pentium Xeon. The Pentium III also incorporates advanced features such as a 32KB L1 cache and either half-core speed 512KB L2 cache or full-core speed on-die 256KB or 512KB L2 with cacheability for up to 4GB of addressable memory space. The PIII also can be used in dual-processing systems with up to 64GB of physical memory. A self-reportable processor serial number gives security, authentication, and system management applications a powerful new tool for identifying individual systems. Because of privacy concerns when the processor was released, you can disable this feature in the system BIOS on most systems that use the Pentium III or Celeron III processors.

Pentium III processors were first made available in Intel's SECC2 form factor, which replaced the more expensive older SEC packaging. The SECC2 package covers only one side of the chip and allows for better heatsink attachment and less overall weight. Architectural features of the Pentium III processor include

• Streaming SIMD extensions (SSE). Seventy new instructions for dramatically faster processing and improved imaging, 3D streaming audio and video, web access, speech recognition, new user interfaces, and other graphics and sound-rich applications.

• Intel processor serial number. The processor serial number serves as an electronic serial number for the processor and, by extension, its system or user. This feature can be enabled or disabled as desired in the BIOS Setup. The serial number enables the system/user to be identified by company internal networks and applications. The processor serial number can be used in applications that benefit from stronger forms of system and user identification, such as:

  • Applications using security capabilities. Managed access to new Internet content and services; electronic document exchange.

  • Manageability applications. Asset management; remote system load and configuration.

Although the initial release of Pentium III processors was made in the improved SECC2 packaging, Intel later switched to the FC-PGA package, which is even less expensive to produce and enables a more direct attachment of the heatsink to the processor core for better cooling. The FC-PGA version plugs into Socket 370 but can be used in Slot 1 with a slot-ket adapter.

All Pentium III processors have either 512KB or 256KB of L2 cache, which runs at either half-core or full-core speed. Pentium III Xeon versions have 512KB, 1MB, or 2MB of L2 cache that runs at full-core speed. The Pentium III Xeon is a more expensive version of the Pentium III designed for servers and workstations. All PIII processor L2 caches can cache up to 4GB of addressable memory space and include ECC capability.

Pentium III processors can be identified by their markings, which are found on the top edge of the processor cartridge. Figure 3.55 shows the format and meaning of the markings.

Table 3.38 shows variations of the Pentium III, indicated by the S-specification number.

Pentium III processors are all clock multiplier locked. This is a means to prevent processor fraud and over-clocking by making the processor work only at a given clock multiplier. Unfortunately, this feature can be bypassed by making modifications to the processor under the cartridge cover, and unscrupulous individuals have been selling lower-speed processors re-marked as higher speeds. It pays to purchase your systems or processors from direct Intel distributors or high-end dealers who do not engage in these practices.

Pentium II/III Xeon

The Pentium II and III processors were the basis for special high-end versions called Pentium II Xeon (introduced in June 1998) and Pentium III Xeon (introduced in March 1999). Intel now uses the term Xeon by itself to refer to Xeon processors based on the Pentium 4. These differ from the standard Pentium II and III in three ways: packaging, cache size, and cache speed.

Pentium II/III Xeon processors use a larger SEC cartridge than the standard PII/III processors, mainly to house a larger internal board with more cache memory.

Besides the larger package, the Xeon processors also include more L2 cache. They were produced in three variations, with 512KB, 1MB, or 2MB of L2 cache.

Even more significant than the size of the cache is its speed. All the cache in the Xeon processors run at the full-core speed. This is difficult to do considering that the cache chips were separate chips on the board in most versions. The original Pentium II Xeon processors had 7.5 million transistors in the main processor die, whereas the later Pentium III Xeon came with 9.5 million. When the Pentium III versions with on-die cache were released, the transistor count went up to 28.1 million transistors in the 256KB cache version, 84 million transistors in the 1MB cache version, and 140 million transistors in the 2MB cache version, which set an industry record at the time. The high transistor counts are due to the on-die L2 cache, which is very transistor intensive. The L2 cache in all Pentium II and III Xeon processors has a full 64GB RAM address range and supports ECC.

Table 3.39 provides an overview of the Pentium II and Pentium III Xeon processors.

^[*] Although this processor is listed as a Xeon by Intel, it's obvious from its specifications that it is really a Pentium III Xeon.

For more details about Pentium II Xeon and Pentium III Xeon processors, see my book Upgrading and Repairing Servers.