Mac Musings

Intel's Promise Fulfilled: More Processing Power per Processor Cycle

Dan Knight - 2009.06.30 - Tip Jar

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An interesting thing has happened since Apple transition to Intel CPUs: Consumer notebooks have moved backward in raw CPU speed yet offer better overall performance.

Geekbench is a benchmark program designed to measures CPU and memory performance. (Geekbench doesn't measure video or hard drive performance.) As processor architecture has improved, as the level 2 (L2) cache has changed size, and as the memory bus has increased in speed, scores have risen to the point where today's 13" 2.23 GHz MacBook Pro (more prosumer than pro or consumer) offers the same level of performance as the Late 2008 2.4 GHz Unibody MacBook despite a 9% difference in CPU speed.

3 Years of Progress

Moving from the original 1.86 GHz Core Duo MacBook to the 1.86 GHz Core 2 Duo version in Late 2006, Geekbench reports a 3.3% higher score. That's due to processor architecture alone, as specs were otherwise identical.

At the 2.0 GHz mark, we see some anomalies: The Late 2008 Unibody model is faster than the Late 2007, which in turn is faster than the Late 2006, yet the Early 2009 MacBook White lags behind the Late 2007 model.

What's going on there?

The Late 2006 MacBook has a 4 MB cache and uses a 667 MHz memory bus.
The Late 2007 MacBook has a 4 MB cache and uses an 800 MHz memory bus.
The Late 2008 Unibody has a 3 MB cache and uses a 1066 MHz memory bus.
The Early 2009 MacBook has a 3 MB cache and uses an 800 MHz memory bus with a 1066 MHz system bus.

The combination of the same CPU speed, the same memory bus, and a smaller L2 cache is what puts the 2.0 GHz MacBook White behind the 2007 model.

Geekbench scores for MacBooks and 13 inch MacBook Pro
Promise fulfilled: Intel CPUs are providing more processing power per CPU cycle.

There are some other interesting results:

The 2.1 GHz Early 2008 MacBook outscores the 2.16 GHz Late 2006 model. The difference: A smaller cache in the CPU but a faster system bus and Intel's "Santa Rosa" chipset.
The 2.13 GHz Early 2009 MacBook outscores the 2.2 GHz Late 2007 model. My guess is that this is due to the switch to Nvidia GeForce 9400M graphics, which I speculate puts less demands on the CPU.
The 2.26 GHz Mid 2009 MacBook Pro matches the 2.4 GHz Late 2008 model, which was only slightly faster than the 2.4 GHz Early 2008 one. (The 2.53 GHz build-to-order 13" MBP scores 3436, about 9.5% faster than the new 2.26 GHz model.)

Frankly, I was stumped by the last one: Same memory bus, same cache size, same basic design, although Apple did add FireWire and an SD Card slot. How could an 9% slower CPU provide the same performance?

Part of it comes from moving from an 800 MHz memory bus to 1066 MHz, but that doesn't account for everything.

Primate Labs gave me part of the answer on its Mac Benchmarks page, which reports exactly which Intel CPU each model uses. The Late 2008 MacBook uses the Intel Core 2 Duo P8600 ("Montevina"), but the Pro model uses the P7550. Both are part of the same "Penryn 3M" family.

And then I noticed a second entry for the 2.26 MHz MacBook Pro, but with an Intel P8400 CPU. This one scored 3126 - virtually identical to the 2.4 GHz Early 2008 MacBook. Curious. Did Apple change CPUs early in the production run?

Whatever the case there, it's evident that Intel has been improving the computing efficiency of its CPUs. You can't predict performance based on CPU speed alone, as there have been architectural improvements going from Core Duo to Core 2 Duo to today's further improved Core 2 Duo processors. You don't have to improve raw clock speed to improve performance.

This time it looks like Intel itself has disproved the Megahertz Myth.

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Dan Knight has been using Macs since 1986, sold Macs for several years, supported them for many more years, and has been publishing Low End Mac since April 1997. If you find Dan's articles helpful, please consider making a donation to his tip jar.

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