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AMD Athlon XP 2400+: The 2800+ may be faster at stock speeds, but you'll be surprised what this "budget" CPU can do at a fraction of the price. Oh, it also overclocks like a champ.
Date: February 3, 2003
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The AMD Thoroughbred initially started with the Athlon 2200+. It marked the transition from the Palomino's 0.18 micron process technology, to the Thoroughbred's 0.13 micron process technology. What the process change was supposed to do was lower voltages, and to reduce the die size. Reducing the size of the chip would result in fitting more on each wafer as they're created. More chips mean more CPUs, and given the laws of supply and demand, hopefully cheaper CPUs for the rest of us.

Anyhow, we're not here to discuss Economics 101. Although the first Thoroughbred was based on the 0.13 micron fab process, there was not much to differentiate between the TBred and Palomino. Although the shape of the core changed, both the old and the new carried the same technology. Despite the expected lower voltages, well, it wasn't really lowered all that much and it still ran very hot, dissipating almost 70W of heat. Overclocking had some potential, but a huge cooler was required for any impressive overclocking. Finally, many enthusiasts were probably a little dissapointed that the TBred still rode on a 133FSB, which was of course, bottlenecking the DDR333 and DDR400 ram types that are so popular these days.

The TBred has matured a lot since June 2002. Commonly referred to as the Thoroughbred "B", the latest TBreds run much cooler than the initial batches, and are much more adept at overclocking than before. The current top-of-the-line TBred is rated at 2800+, and runs on a 166FSB (as well as the 2700+). As mentioned in our last paragraph, the previous Athlons bottlenecked the faster ram types, but now it should sync better with DDR333. There is a price to pay though if you want that speed, which makes another TBred "B", the 2400+ provided by our friends at , that we'll be looking at today a very popular choice. Unfortunently, the 2400+ is a 133FSB part, but as we'll see later on, we can fix that. :)

The Athlon Thoroughbred 2400+

Click to Enlarge

The TBred is based on the OPGA, or organic pin grid array, packaging technology. The benefit over ceramics (used in the Thunderbirds) is two-fold as it lowers the impedance and the cost of the CPU. Technology-wise, it carries the same featureset as the Palominos. You can grab the key architectural features on their . Here are sone of the highlights...

QuantiSpeed Architecture for enhanced performance: One of QuantiSpeed's key features is the advanced hardware prefetch. What this does is that it allows the CPU to anticipate, or guess, what will be done next and move that information to the cache for faster access. Say if you're working on a word document. The processor follows you as you work, and predicts what you're going to do next. Say that you plan to check for spelling. If the processor guesses correctly, your spell check will open a lot faster. Of course, if it guesses wrong, the cached data is discarded. Thanks to the shorter pipeline, this isn't as noticeable as it would be for the longer pipelined Pentium 4.

3DNow! Professional technology for leading-edge 3D operation: The original 3DNow! instructions are present in the Athlon XP, as well as 52 SSE instructions to take advantage of multimedia apps that use Intel's SSE. In reality, little improvement is present in day-to-day work with SSE & 3DNow!, but if you're a Photoshop "Blur" junkie, then you'll appreciate the extra instructions.

333MHz and 266Mhz: As mentioned earlier, the newest TBreds support the 333FSB (166FSB double pumped) natively, though the one we'll be looking at is a 266FSB part.

Performance-enhancing cache memory: There are 64K instruction and 64K data cache for a total of 128K L1 cache. Add 256K of integrated, on-chip L2 cache and you have a total of 384K full-speed, on-chip cache. A little more cache would certainly help, but we'll have to wait for Barton and Hammer for that.

Die size: approximately 37.6 million transistors on 84mm2: The die size is one physical change from the Palomino, which measured 128mm2, and was based on the 0.18 micron fab process. The TBred shrinks things down by about 55%, and is based on the 0.13 micron copper fab process. Like the Palomino, the TBreds come out of their facilities in Dresden, Germany.

As it has always been since the release of the XP, AMD uses a performance rating to market its products. The Athlon XP 2400+ does not run at 2.4GHz, but rather, 2.0GHz (15x133). To get an idea of how AMD determines it's performance rating, take a look at this graph...

Click to Enlarge

According to AMD, there are two factors in determining CPU performance, and that is the instructions per clock cycle (IPC) and clock speed, and I quote... "Until recently, the IPC of most computer processors was identical, so clock speed alone was used to determine performance capability. In current processors, however, IPC is different for competing processors, so performance is defined using both IPC and frequency. The end result is that frequency alone no longer determines performance. As a result of its QuantiSpeed architecture, the AMD Athlon XP processor has an optimum balance of IPC and frequency to achieve high levels of real world PC application performance."

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