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The tradeoffs between AMD’s Phenom and FX CPUs

Micro Center is dangling some dirt, dirt cheap AMD CPUs these days, which has me thinking. I have a couple of pokey machines hanging around that I don’t use very much, so what if I modernized one of them?

The current-generation FX processors are cheap, but previous-generation Phenom CPUs are even cheaper. What to do?

So I researched it a little.

Given the same clock rate and same number of cores, a Phenom is about 20% faster than an FX–when doing mathematically intensive work.

So for around $100, I could get a 6-core Phenom clocked at 2.7 GHz, or for $10 more, a 6-core FX clocked at 3.3 GHz.

The peak wattage on the CPUs is comparable, though the FX may have a slight edge in everday use, because it’s built on a newer foundry process. The 95-watt rating is its theoretical maximum, when the CPU is running at full throttle. When the CPU is idling, power consumption drops, and generally speaking, the newer process will use less wattage when it’s sitting at idle.

The peak turbo speed of the FX is 3.9 GHz, vs. the Phenom’s peak turbo speed of 3.2 GHz. That’s a 22% difference, but the architectural difference will chew that up, at least some of the time.

I look at the FX as today’s 486SX. If you recall, two decades ago Intel and AMD released budget versions of the 486 that lacked a floating-point unit. I bought a 66 MHz 486SX, which was about the same price as a 33 MHz 486DX, and although I certainly lost bragging rights, I never noticed the difference between a DX and SX since the three programs that occupied most of my CPU time were Word, Civilization and Railroad Tycoon. For that kind of stuff, the extra clock cycles were more valuable than the math coprocessor.

The FX doesn’t omit the math coprocessor–it just contains half as many of them, groups the cores into pairs, and shares the coprocessors between them.

The Bulldozer architecture AMD FX is a bit of a disappointment, from an enthusiast perspective. If you need a fast, inexpensive PC and your typical uses are something other than 3D gaming or other mathematically intensive tasks, it’s not a bad chip for that. The disappointment is completely understandable, though. For 40 years, we’ve grown used to the new generation of CPUs being better than what came before it, no thinking required.

I’d almost talked myself into an FX, but the more I think about it, the more I think I’d be better off either pocketing the $10, or putting the $10 toward a nicer motherboard.

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