IBM vs. Intel - Performance per Watt

At Steve Jobs' WWDC 2005 Keynote, he presented this slide to the curious crowd:

The idea was that IBM couldn't deliver the performance per watt that Intel could over the coming years, and that was one of the primary reasons for the transition away from the PowerPC architecture.

While we can't test future IBM and Intel CPUs, we can definitely compare power consumption and performance per watt today and find out if Intel can at least start delivering on Apple's claims.

I started out by looking at power consumption of the iMac systems as a whole, measured at the power outlet in Watts. The systems are configured as close to identical as possible; although the Core Duo iMac has a slight advantage in its 90nm X1600 GPU compared to the iMac G5's 0.13-micron X600 GPU, I didn't focus on any GPU intensive tests so the difference should be minimized. There are obvious memory differences as well. While both systems have 512MB of memory, the Intel system uses DDR2-667 and the G5 system uses DDR2-533. Then there are the CPU and chipset differences, but those are the ones that we want to measure anyways, so they have to be there.

The first comparison is system power consumption at idle. This is with both identically configured systems being freshly booted and sitting on the desktop with no disk accesses or anything. Note that the systems weren't left alone long enough for the hard drive to spin down yet:

Total System Power Consumption at Idle

The Intel based iMac consumes about 2/3 of the power of the iMac G5 - impressive and pretty much expected given what we've seen of the Core Duo in the past. The G5 is a solid competitor here, but the Core Duo is in a completely different league of power consumption.

Total System Power Consumption under Load (iTunes)

Under load, the difference in power consumption is just as pronounced - with the iMac G5 coming in at 96W while the Intel based iMac is at 62W. Once again, we are looking at approximately 2/3 the system level power consumption from the Intel based iMac.

I also looked at power consumption during my H.264 encode test, which produced results similar to the iTunes encoding test above:

Total System Power Consumption under Load (Quicktime H.264)
The iMac Core Solo 1.83GHz was simulated by disabling one of the Core Duo's cores


But now let's look at performance per watt and see where we stand today. I took the Quicktime H.264 encode time and converted it into frames encoded per second, then divided that by the peak power consumption values for the entire system. Note that during the Quicktime and iTunes encoding tests, the peak power consumption value and the average power consumption of the system are basically identical, since the CPU remains at close to 100% utilization for the entire duration of the test.

The end result is this graph of Frames per Second/Watt:

Performance per Watt - Quicktime H.264 Encoding
The iMac Core Solo 1.83GHz was simulated by disabling one of the Core Duo's cores

It looks like with the Core Duo, Apple does have better performance per watt than with the G5. The Core Duo based iMac offers about 90% higher performance per watt than the iMac G5. Even when looking at single core performance, the performance per watt is higher, although not nearly by as great of a margin at 19.7%. It is worth noting that Intel's performance-per-watt advantage would be severely diminished if we were comparing to a 65nm G5 processor, which as of yet does not exist. By the time that IBM is shipping 65nm desktop processors in volume, I'd expect Conroe/Merom to be out and both of those cores are supposed to offer greater performance (both directly and on a performance per watt basis) than Core Duo, so it is possible for Intel's advantage to continue on into the future.

We are only talking about system power usage here, so if we were to truly isolate just the CPU power, the difference should be even larger, assuming that the rest of the systems consume a relatively equal amount of power in both configurations. You should also keep in mind that the Quicktime encode test is actually one of the Core Duo's weakest tests, so the actual performance per watt advantage may be even higher in tests where the Core Duo has a larger performance advantage over the G5. This is just a good test to show power consumption, since it is fairly CPU bound and consistent in its CPU load.

Core Duo vs. G5 Architecture and Memory Performance
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  • Anand Lal Shimpi - Tuesday, January 31, 2006 - link

    Turning off one core leaves the full 2MB of cache for the other core to use since it is a shared L2.

    Take care,
    Anand
    Reply
  • Eug - Tuesday, January 31, 2006 - link

    quote:

    Turning off one core leaves the full 2MB of cache for the other core to use since it is a shared L2.

    Take care,
    Anand

    Cool thanks.

    P.S. I have read elsewhere that the new iMac Core Duo uses less than half of the CPU's processing power to play back H.264 Hi-Def 1920x1080 video at a full 24 fps. If true, that's great, because my iMac 2.0 chokes on that. It plays back relatively smoothly, but only at about 12-15 fps.

    That bodes well for a future single-core Yonah Mac mini.

    Then again, probably not, considering that I suspect the iMac Core Duo does so well on H.264 playback because of its Radeon X1600. I'd doubt the Mac mini would get anything close to that any time soon.
    Reply
  • Anand Lal Shimpi - Tuesday, January 31, 2006 - link

    Max CPU utilization (across both CPUs) when playing a 1080p stream scaled to fit the screen is about 60%, but it usually hovers below 50%. I am not sure whether or not the X1600's H.264 decode acceleration is taken advantage of (I doubt it), I'm trying to find out now. Also remember that on the PC side, the X1600 will only accelerate up to 720p.

    Take care,
    Anand

    Reply
  • Anand Lal Shimpi - Tuesday, January 31, 2006 - link

    I just confirmed with ATI, the X1600's H.264 decode acceleration is currently not supported under OS X. ATI is working with Apple on trying to get the support built in, but currently it isn't there.

    Take care,
    Anand
    Reply
  • Eug - Tuesday, January 31, 2006 - link

    quote:

    I just confirmed with ATI, the X1600's H.264 decode acceleration is currently not supported under OS X. ATI is working with Apple on trying to get the support built in, but currently it isn't there.

    Thanks again for the info. That's actually good news in a way. Things are looking up for that single-core Yonah Mac mini HTPC.
    Reply
  • andrep74 - Tuesday, January 31, 2006 - link

    Isn't performance/Watt a function of the CPU, not the platform? Reply
  • Kyteland - Tuesday, January 31, 2006 - link

    That picture of Jobs doesn't say "PC vs Intel" it says "PowerPC vs Intel". Jobs is just standing in the way. He's comparing the old mac to the new mac. Reply
  • Calin - Tuesday, January 31, 2006 - link

    You could think about it that way - but in the end, the buyer is interested on the total energy consumption/heat production (as this is what he pays for, and what he must get rid of).
    Have you heard of the Toyota D4D engine? It has a record of 2.4 liter (less than a gallon) diesel fuel used per a hundred kilometers (60 miles). However, the same engine on a Land Cruiser 4x4 all options will get you much less (four times less maybe).
    It doesn't worths talking about performance per watt at the processor level, it is better at the platform level.
    Reply
  • BUBKA - Tuesday, January 31, 2006 - link

    Were these benches done with a USB 2.0 device plugged in? Reply
  • Furen - Tuesday, January 31, 2006 - link

    I was under the impression that Intel was blaming Microsoft for that, so that would not apply to OSX, though if the driver works perfectly for every platform except Napa I'd guess its a hardware problem that MS will fix in software (which is well enough as long as it works). The power consumption difference is probably less than 10W anyway. It matters on a notebook but hardly matters with a desktop.

    Reply

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