Apple Seeds iOS 5.0.1 Beta 2 to Developers

It never occurred to you that a dual core CPU and the new OS might be a bit more battery hungry, and is more likely to be causing the difference? My phone still ends the day at ~55% with average usage. Yesterday I had 6 hours usage, 18 hours standby before I got to 20%. That seems fairly reasonable.

Well there are two things you need to figure on mobile hardware design. One is that the screen is nearly always, by far, the most power hungry component. Turning the backlight off can save you 50% of the power consumption on most systems. Behind that, the RAM, any storage, wireless and then things like CPUs (in that order) are what starts to reduce your battery life.

Apple have done an incredible job in basically turning your phone off completely when you are not using it; when the screen is black and you have to hit the top button to get to the slide-to-unlock display, you are waking it up from full standby where nearly everything is off. That's how you get decent battery life on phones, make sure they are not turned on all the time, as with everything running even with decent screen management they'd all barely last 2 hours of runtime.

The second thing is that clocking things down aggressively and turning things off is not always the best solution for situations where you need to DO something. While it's sitting on a desk, nothing on the network locking wireless, screen off, power management is great, but otherwise you are nearly always better off in a "race to idle" scenario. This is where you simply run as fast as you can to get the work off the table so that you can go back to a state where you can actively power manage. Since you can run at 800MHz and get "800 million things done a second" (not realistic, but bear with me) doing 100 million things will take 1/8th of a second. At 400MHz it will take 1/4 of a second. At 166MHz it will take 2/3 of a second. It is usually much better to run at full power for 0.125 seconds than at 20% of the speed (and probably only 50% of the power consumption of full) for 0.7 seconds, or incur the time taken to switch.

So what Apple tend to do (and what most mobile manufacturers, CPU schedulers and power management libraries do as well) is keep the CPU running as fast as possible for as long a time as is necessary plus a little bit more. The moment you take an input, you ramp up the CPU, and until you are dead sure that the user is idle, you stay there. This works on mobile devices without impacting power management too much because as above the CPU is by far the least impact on the battery life.

That, and the Cortex-A9 class dual-core CPUs (Apple A5) are more efficient than the Cortex-A8 (Apple A4) when one core is idle and not greatly more power hungry when both cores are active at the same clock speed. They are also more efficient from an instruction scheduling point of view. So bumping from an A4 to an A5 from iPhone 4 to iPhone 4S wouldn't actually make a great deal of difference. Graphics cores are the same way.

For wireless, Bluetooth 2.1 has a cute feature in that it can support something like 24Mbps data transfers compared to older standards which can only do around 10Mbps. The same race to idle scenario applies here; it only powers the transmitter to send data (reception is tantamount to passive) so to send 24Mbit of data in 1 second uses less power than sending 24Mbit of data at a lower speed over more than 2 seconds. Holding that transmitter powered is what gives you the better power consumption even though actually sending at 24Mbps using the EDR rate uses more power at any sampled point, it is active for less time when you add it all together.

The 4S also does have a smaller battery, which is supposed to be made up for by more efficient components..

All in all, it is more likely that Apple simply are not using a more aggressive power saving strategy when they can on certain parts of the iPhone 4S that are brand new to the 4S compared to the 4. Probably the new GSM/CDMA chip (putting it into an idle state instead of a nap or sleep state, this is my personal opinion of the culprit based on the talk time numbers for the 4 vs. 4S - they are too significantly different to explain it being a battery size issue, and while on the phone with it to your ear, the proximity sensor has allowed the screen and much of everything else to be turned off, and all it needs to do is route the audio to the GSM chip, so the GSM chip must be using a ton of extra power in comparison. Driving two antennas, and boosting power for better signal would account for it)

.. or Bluetooth 4.0 (keeping the Low Energy link active accidentally) or even using NAND with a different page size and having to do more aggressive or time consuming bad block handling or page buffering.

... or something else. But it's a lot more complicated than "there are two CPUs instead of one so it will take more power". Dual core (say, a Core i5) laptops these days use a lot less power than single core ones (say, a Pentium M) at much higher clocks.

800 megabytes for a delta? SiriOSly?

Well, clearly it's not a delta. ;)

Can anyone with an iPhone 4S who is running Beta 2 confirm if the battery life is better?

I get horrible battery life, like 69% at 2 and a half hours of very standard usage. Twitter, couple calls, sms, etc. This is ridiculous.

Uhh, this update came out what... 30 minutes ago?

800 MB on 4S.
45.8 MB on iPad 2 GSM.

There must be a whole lot more changes on the 4S eh?

800 MB download on 4S.:eek::rolleyes::mad::apple:

They must be replacing the entire OS, then.

Makes you wonder what is borked so bad that they can't patch it with a delta.

Thats what she said.

Or in my case as a gay man, thats what HE said

I'm still amazed at how such a large and rich company, with such a tiny and very tightly controlled range of products, can so screw such basic things up each time.

If Apple made a dozen phones, a dozen iPads ect ect all with different CPU's, screen resolutions etc etc then I could forgive them, but really. This should not be acceptable from a supposed brand leader.

Esp, as I said given their extremal small range of products and the length of time they have had to get this right before launch.