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ED#131 : CPU Idling Problem In The Apple iPhone 4S?(This Stupid App Doesn't Work!) Rev. 2.1
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ED#131 : CPU Idling Problem In The Apple iPhone 4S? (This Stupid App Doesn't Work!)

The Apple iPhone 4S might be a small upgrade if you were using the iPhone 4, but it is a huge upgrade if you are upgrading from the iPhone 3GS, as I was. Not only was the screen much sharper (albeit still the same size!), the iPhone 4S was much faster. Unfortunately, I also immediately noticed a big problem with the iPhone 4S - its terrible battery life.

This was partly due to the iPhone 4S' inability to turn off 3G. Yes, if you did not notice yet, you cannot turn off the 3G network on the new iPhone 4S. The option was disabled by Apple although we understand that it might be re-enabled in a coming update.

However, the constant use of the 3G chip still cannot explain how the iPhone 4S uses so much power. It is now virtually impossible to get through a full day of hard use. Even if I leave the phone virtually idle, it wouldn't last more than one and a half day. That actually makes it worse than my iPhone 3GS! In the end, I had no choice but to pair it with the Mophie Juice Pack Air battery case. A standard case or bumper was just not a realistic option unless I wanted to bring my charger wherever I go!

This brings us to the perplexing issue... why is the iPhone 4S' battery life so bad? This isn't a problem with the iPhone 4 as my sister-in-law is using one and has had absolutely no problem with its battery life. She can play games on her iPhone 4 the whole day and have more than half the battery capacity at the end of the day! That is totally impossible on the iPhone 4S - I killed over 30% of my battery life just by playing an hour of Monopoly!

Recently, my brother pointed me to a very nice app called System Monitor with Battery Max. It's a 99 cent app that allows you to monitor the hardware and software of your iDevice. What's really nifty about it was it was able to give me a live read of the iPhone 4S' CPU load. What we found shocked us - the Apple iPhone 4S had a constantly high CPU load even when it idles!

Update @ 08/02/2012 : It looks like this app wasn't as well-designed as we thought it was. Please do NOT buy it. As of this date, it appears that the developer failed to account for the dual-core nature of the iPhone 4S' A5 processor, thereby increasing its CPU load by 50%. See the second page for the evidence.

Update @ 10/02/2012 : Thanks to the iPad 2 results from zy, we have just confirmed that this app is being fooled by the presence of two processor cores in the Apple A5 processor, and thereby falsely reporting its CPU load at idle. More details in the following page.

Learn how to protect your Apple iPhone's Home button from premature failure!


CPU Load @ Idle

Take a look at the following screenshots of the CPU loads of various iDevices at idle. To ensure consistency, we rebooted the iDevice and let it finish loading its various processes (which would result in a high CPU load) before capturing the CPU load at idle.

Apple iPhone 4S

Apple iPhone 4

Apple iPhone 3GS

Apple iPad

Apple iPod touch 4G

Apple iPod touch 3G

Well, the results pretty much speak for themselves. The iPhone 4 and iPhone 3GS smartphones have an idle CPU load below 20%. The original Apple iPad idles at just 8%. But for some reason, the new iPhone 4S idles at over 52%!

That means the iPhone 4S' idle CPU load is 2.7X higher than that of the iPhone 3GS, 4X higher than the iPhone 4 and 6.6X higher than the iPad. Little wonder why it cannot even maintain the same battery life as the iPhone 4 despite the slightly higher battery capacity.

Let's take a closer look at the CPU load...


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