When Is 2.1 GHz Slower than 2.0 GHz? When It's the New MacBook

Remember the Megahertz Myth? It held the widespread belief that a computer with a faster processor clock speed was more powerful than one with a slower CPU.

Apple demolished that with the PowerPC G3 and G4 processors, and with the transition from Pentium 4 to Core, Intel demonstrated the same thing. A CPU with a slower clock speed can be more powerful than one that runs at a higher MHz rating.

Pay attention, because Apple just took a step backward with its entry-level MacBook and 15" MacBook Pro models. The previous version of these computers included a 4 MB on-chip level 2 (L2) cache; the replacements introduced last month use the new Penryn CPU, and the slower version only has a 3 MB L2 cache.

We initially suggested that the 5% difference in clock speed between the 2.0 GHz Core 2 Duo in the October 2007 MacBook and the 2.1 GHz Core 2 Duo in the February 2008 MacBook would be generally imperceptible to users. That's still true.

What we hadn't expected was that the first benchmark results show the 2.1 GHz MacBook has lower overall performance than the 2.0 GHz MacBook it replaces. Primate Labs, creators of the cross-platform Geekbench program (which measures only CPU and memory performance, not drives or video), report the following overall results:

• 2.0 GHz MacBook (2007), 2668
• 2.2 GHz MacBook (2007), 2890
• 2.1 GHz MacBook (2008), 2617
• 2.4 GHz MacBook (2008), 3135

Compare those numbers. The new 2.1 GHz MacBook, which you'd intuitively expect to outperform the 2.0 GHz model, comes in with a lower benchmark score. It's only 2% lower, but you'd expect a 5% faster CPU would make things better, not worse. Blame the smaller L2 cache.

On the top end, the 2.4 GHz MacBook scores 8.5% higher than last year's 2.2 GHz MacBook, which is almost exactly what you'd expect from a 9% faster CPU.

Primate Labs also reported on the new MacBook Pro models last week. There the entry-level 2.4 GHz model has a 3 MB L2 cache, but the 2.5 GHz (as well as the 2.6 GHz build-to-order option) include a 6 MB L2 cache. Here are the overall performance numbers:

• 2.4 GHz (mid-2007), 3107
• 2.6 GHz (mid-2007), 3245
• 2.4 GHz (early 2008), 3047
• 2.5 GHz (early 2008), 3228

Once again, the entry-level model is slower than the model it replaces. Again, it's just 2% and imperceptible in use, but it's a sad day when the newer model is slower than the one it replaces.

That said, the 6 MB L2 cache in the 2.5 GHz Penryn struts its stuff. Geekbench measures it at just 0.5% slower than the 2.6 GHz Merom in the mid-2007 MacBook Pro. Impressive! And the 2.6 GHz build-to-order MacBook Pro should be about 4% faster.

Reality Check

We're making a big deal over something that won't make much of a difference in the real world, but we want buyers to understand that the new 2.4 GHz and slower Books are slightly slower than the models they replace. If anything, this makes the close-out deals better values than we had first believed.

We also want to remind Mac fans that you pay a huge premium for a bit more power. The difference between 2.5 GHz and 2.6 GHz is less than 6%, and Apple charges $250 for the upgrade. That's about 10% of the MacBook Pro's price, and you're only gaining in one are: raw processing power. And only by 6%.

There's a bigger difference with the consumer MacBook. The difference between 2.1 GHz and 2.4 GHz is 14%, and Geekbench measures the performance difference at 20%. You do pay an 18% premium to get the 2.4 GHz white MacBook over the 2.1 GHz entry-level model, and for the extra processing power, additional RAM, increased drive space, and move from a Combo drive to a SuperDrive, it's the value champion.

Buying Decisions

Were I buying a MacBook today, I'd grab one of the black 2.2 GHz MacBooks while supplies last. Prices have been seriously slashed, and it is one beautiful computer. It provides plenty of power, and the 13.3" screen should be enough for most users. It's a steal.

Were I contemplating a 15" MacBook Pro, the close-out deals on the 2007 models make them both excellent buys right now. Ditto for the few 2.33 GHz models left in stock, which I consider the value champion among 15" models.

There aren't too many times when having 5-10% more power is going to make a perceptible difference in your day-to-day use, so we generally recommend buying the model that has the features you need. You're generally better off buying the slower 'Book and investing the price difference in maxing out RAM and putting in a faster and/or larger hard drive.

And we can't imagine a situation where it would be worth paying $250 for the 2.6 GHz upgrade, unless bragging rights mean a lot to you.

Since publishing this, Macworld has benchmarked the new MacBooks. According to their tests, the 2.1 GHz MacBook is faster than the 2.2 GHz model. Just goest to show that every benchmark measures things differently. dk