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Athlon XP Barton

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Athlon XP Barton

Introduction

On February 10, 2003, AMD introduced the AMD Athlon XP 3000+ processor. As the name implies, this processor is now AMD’s fastest-performing Athlon XP processor, surpassing the 2800+. However, this new processor is new in more than just its performance: it represents the first model based on a new Athlon XP core, code-named “Barton”. In this article, you will learn more about the Barton core, how AMD has used its design to boost Athlon XP performance, and how the Athlon XP 3000+ compares in performance to the 2800+ and the 3.06GHz Intel Pentium 4 processors.

Barton’s Predecessors – A Very Short Athlon History

The Barton core is the seventh major revision of the Athlon core, and the fifth one made for AMD’s Socket A since the original Slot A-based Athlon processors were introduced back in 1999. While the original Athlon’s Pluto and second-generation Orion processor designs had 512KB of L2 cache, the external cache memory ran at just one-half to as little as one-third of the processor's core speed. You'll find a complete breakdown of these processors in Chapter 3 of Upgrading and Repairing PCs, 14th Edition.

Starting with Athlons based on the Thunderbird core, sold in both the original Slot A and current Socket A (Socket 462) form factors, AMD dumped slow external L2 cache for full-speed on-die L2 cache. However, AMD also reduced the size of Athlon’s L2 cache from 512KB down to 256KB in the Thunderbird. The Athlon XP’s Palomino, Thoroughbred-A and Thoroughbred-B cores had improvements in cache design, but cache size remained at 256KB until the advent of the Barton core.

Barton’s Difference: More Cache, Not More Clock Speed

While Barton-core Athlon XP processors have all the features of previous Athlon XP processors, there’s one major difference: Barton combines the full-speed L2 cache design of Thunderbird and its successors with the larger 512KB cache size of the original Athlon processors. Thus, Barton-core Athlon XP processors have a more efficient memory design than any previous Athlon processor. Main memory access is also faster, as Barton bids farewell to the 133MHz clock multiplier and 266MHz (133 times 2) front-side bus used by most previous Athlon XP models. All Barton-core Athlon XP processors use the 166MHz clock multiplier and 333 (166 times 2) front-side bus that is also used by the Athlon XP 2700+ and 2800+ processors.

However, Barton’s performance rating naming system doesn’t reflect higher clock speeds. While the first Barton-core processor, the Athlon XP 3000+, has a name indicating it has faster performance than its predecessor, the Athlon XP 2800+, the 3000+’s actual clock speed is actually a bit slower. Table 1 compares the actual clock speeds of the initial Barton-core processors (marked in Boldface) to current to the actual speeds of Athlon XP processors based on the Thoroughbred-B processors.

Athlon XP Processor

Core Type

Compared to Pentium 4 Processor

Actual Clock Speed

L2 Cache Size

FSB Speed

2500+

Barton

2.53GHz

1.833GHz

512KB

333MHz

2400+

Thoroughbred-B

2.4GHz

2.000GHz

256KB

266MHz

2600+

Thoroughbred-B

2.66GHz

2.083GHz

256KB

333MHz

2800+

Barton

2.8GHz

2.083GHz

512KB

333MHz

2600+

Thoroughbred-B

2.66GHz

2.133GHz

256KB

266MHz

2700+

Thoroughbred-B

2.66GHz

2.167GHz

256KB

333MHz

3000+

Barton

3.06GHz

2.167GHz

512KB

333MHz

2800+

Thoroughbred-B

2.8GHz

2.250GHz

256KB

333MHz

Table 1 – Recent Athlon XP Processors Ranked by Actual Clock Speed

As Table 1 makes clear, all three of the initial Barton-core processors have slower clock speeds than the same or similar performance-rated Thoroughbred-B processors, while the 3000+ is almost identical in clock speed to the Thoroughbred-B version of the 2800+. However, benchmark tests performed by AMD and third parties indicate that the Barton-core Athlon XP processors have higher overall performance than comparable Thoroughbred-B processors. Why is this?

As I discuss in Chapter 3 of Upgrading and Repairing PCs, the size and speed of cache memory has a huge impact on system performance: more cache and faster cache boost performance over less cache and slower cache memory. AMD’s doubling of full-speed L2 cache size on the Barton-core processors does lead to better system performance than that achieved with the previous Thoroughbred-B core, although third-party benchmarks don’t always indicate as wide a performance difference as AMD’s performance-rating name scheme might imply.

Barton or Thoroughbred? Discovering the Difference
Since AMD is replacing its short-lived Thoroughbred-B version of the Athlon XP 2800+ with the Barton version, it might be important to you to learn how to distinguish the processors. To make room for Barton’s additional 256KB of L2 cache, the processor core is wider than the one used by the Thoroughbred-B (see Figure 1).


(Click for Larger Image)

Figure 1
The Athlon XP processor based on the Thoroughbred-B core (left) compared to the Barton core (right). Arrow points to processor core.

Unfortunately, markings on retail packages might not indicate which processor is which. If you are unsure of which processor you are buying, ask the vendor to tell you the exact model number. Thoroughbred-core Athlon XP processors are known as Model 8 processors, while Barton-core Athlon XP processors are known as Model 10 processors.

The model numbers of the processors listed in Table 1 are listed in Table 2.

Athlon XP Processor

Core Type

Model Number

2400+

Thoroughbred-B

AXDA2400DKV3C

2500+

Barton

AXDA2500DKV4D

2600+

Thoroughbred-B

AXDA2600DKV3C (266MHz)

AXDA2600DKV3D (333MHz)

2700+

Thoroughbred-B

AXDA2700DKV3D

2800+

Thoroughbred-B

AXDA2800DKV3D

2800+

Barton

AXDA2800DKV4D

3000+

Barton

AXDA3000DKV4D

Table 2 – Recent Athlon XP Processors by Model Number

Note that the last two digits of the model number indicate L2 cache size and FSB speed. A "3" indicates 256KB L2 cache, while "4" indicates 512KB L2 cache. A "C" indicates 266MHz FSB, while "D" indicates 333MHz FSB.

Comparing the Athlon XP 3000+ to Its Rivals

AMD calls the Athlon XP 3000+ the “World Highest Performing Desktop PC Processor” in its February 10th press release, and based on the benchmarks selected, AMD makes a good case for this claim. However, when different software and hardware are used to benchmark the Athlon XP 3000+ and the Pentium 4 3.06GHz, results may vary.

The third-party benchmark tests performed by Tom’s Hardware and Anandtech on the Athlon XP 3000+, Athlon XP 2800+ (Thoroughbred-B core) and Pentium 4 3.06GHz tell a different story. While the Athlon XP 3000+ is faster than its stable mate, it’s also slower than the Pentium 4 3.06GHz on most tests. Generally, where cache memory is the most important factor, such as in office applications, gaming, and content creation, the Athlon XP 3000+ is a good choice, although the 3.06GHz Pentium 4 might still be a bit faster. However, where processor clock speed is the deciding factor, such as in 3D rendering, multimedia encoding, and archiving, both the Pentium 4 and the Athlon XP 2800+ Thoroughbred-B are usually faster.

Barton’s Future

With the introduction of the Athlon 64 (code-named Clawhammer and K8) in the second half of 2003, the Barton-core versions of the Athlon XP are likely to be the last Athlon XP processors produced. Before that happens, AMD plans to ship the Athlon XP 3200+, and move its Athlon MP (multiprocessing) and Mobile Athlon XP (notebook) processors to the Barton core.

AMD has squeezed a lot of performance out of the Athlon design, but its adoption of larger cache rather than higher clock speed in its initial Barton-core processors seems to suggest that the current Athlon architecture has just about reached its clock speed limit.

For Further Research

AMD’s official Athlon XP website has been updated to reflect the Barton core:
http://www.amd.com/......18_1274_3734^3736,00.html

For more information on the Athlon XP architecture and the performance rating system used by AMD for numbering different Athlon XP models, see my original article.

Anandtech’s latest Pentium 4 versus Athlon XP full-line tests including the P4 3.06GHz and Athlon XP 3000+ now graph which processor is faster at any given speed or model number for all benchmarks. See it at http://www.anandtech.com/cpu/showdoc.html?i=1783&p=1

Tom’s Hardware’s latest Pentium 4 versus Athlon XP full-line tests also include overclocking results and methods. See it at http://www.tomshardware.com/cpu/20030210/index.html

Copyright©2003 Pearson Education. All rights reserved.

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