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) packageor 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.

• 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.

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:

• 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 the following table 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), you can find out the exact specification including socket type, voltage, stepping, cache size, and other information about the chip.