Run your MacBook without a battery and throttle the performance

Battery_arms_114466I am still trying to get my head around this article on Gearlog that points out that Apple notebooks throttle the CPU performance if you run them plugged in without a battery installed.  They discovered this "feature" by accident while performing benchmarks with different types of RAM.  They kept seeing different results and then figured out that the benchmarks run on the MacBook Pro while plugged in but without the battery installed consistently clocked in with 37% lower performance.

You may want to read that last sentence again.  If you pull the battery out of your MacBook Pro and run it while plugged into the power outlet your MBP will slow down almost 40%.  This intrigued the Gearlog folks so they went digging and found a discussion on the Apple support document that describes what is going on:

If the battery is removed from a MacBook or MacBook Pro, the computerwill automatically reduce the processor speed. This prevents thecomputer from shutting down if it demands more power than the A/Cadaptor alone can provide.

Say what?  That doesn’t make sense to me as I wouldn’t think that any notebook would be drawing power from both the adapter and the battery at the same time anyway.  Any electrical engineers out there who can explain this?  Do other non-Apple notebooks do this?  Has anybody seen this first-hand?  Inquiring minds want to know. 


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