[Android General] cajunflavoredbob:
Introduction:

If you’re reading this, I’m going to assume that you want to learn something new. I love sharing knowledge with others, so I hope you do as well. With that being said, please understand that I’m doing this in my spare time, and have no degree of any kind on this topic. What I’ve compiled here is a pretty good guide to explain and hopefully educate some of you on a highly talked about, but widely misunderstood concept of CPU architecture.

Before we begin, I need to make sure you all understand a few basic concepts of electricity. I can’t teach you new material if you don’t know the language, right?

Terminology:

Voltage

The first term is, of course, voltage. Voltage is defined as the difference in electrical potential between two points. What does that mean, I’m sure you wonder? Well, to put it simply, think of a fire hydrant. When the valve is opened to let water into a hose, from the hydrant, it rushes in all at once to the end of the hose. It sits there in the hose until the nozzle is opened to put out the fire. The force that pushes the water forward is called water pressure, and like water pressure, voltage pushes the electrical current along as well. So, we will think of voltage itself as the force or pressure being applied behind an electrical current to keep it moving.

Amperage

Next up is the term, amperes. In short this is the electrical current itself. An ampere, or amp for short, is the actual unit of measurement for the amount of electricity passing a single point in a circuit at one time. This might seem confusing, so let’s just keep it simple and think of an amp as the electrical current itself. In the fire hose example, the amperage would be the water inside the hose.

Wattage

Last up is something called a watt. Now, this one can get tricky, so stick with me. A watt literally measures the rate of energy conversion or the transfer of energy. So, essentially, the watt measures the amount of work done over time. This is where it gets tricky and a little confusing. Wattage, in the fire hose example, would be the amount of water that the fire hose can hold. This is the work, or wattage, generated by the hose while operating under a constant flow of water. Now, that’s the tricky part right there. ‘Work’ in this example isn’t a normal 9-5 job. It is, more simply put, the overall capacity of the hose. A normal household lightbulb is rated around 60 watts. This means that while it’s on, it is producing a constant amount of light. This constant amount is 60 watts, which is its peak brightness under constant current.

So, to sum these three terms up as simply as possible, think of voltage as pressure, amperage as the current, and wattage as the capacity.

Example

One final example should help with this analogy. We’ve all seen those wacky waving inflatable arm flailing tubemen before, right? If not, or if you’ve never seen Family Guy before, it’s basically a long, nylon tube that is open at both ends. One end is attached to a fan at the bottom, while the other end is left open for air to escape. When the fan at the bottom is turned on, it begins to generate wind that inflates the tube and causes it to rise off the ground and flail about in the air. In this example, the voltage is the air pressure keeping the tube floating, the wind flowing through the tube is the amperage, and the amount of wind needed to make the tube rise off the ground is called the wattage.

Undervolting:

Myth or fact?

Let’s go ahead and start off with a bang, shall we? First, let me make it clear to you that no matter what people tell you, undervolting your CPU will not magically make your battery last five days longer than it should. I’m not saying it doesn’t save battery at all, because it does. It just doesn’t save as much as you’ve probably been led to believe. On any average smartphone battery under normal conditions, you should not expect an increase of more than a few percent while undervolting.

Does this mean you should stop undervolting altogether? Not at all! Quite the contrary, actually. Undervolting is actually a very good thing for your smart phone when you do it correctly. Undervolting has one major positive effect on your CPU: it will extend the life of your processor by allowing it to do demanding things with lower heat generation. In the tube example from before, undervolting would be like reducing the fan speed as low as possible while still keeping the tube in the air. The air pressure lowers along with the wind current, or amperage. Due to the now lower amount of pressure, the amount of wind being pushed through the tube (amperage, remember?) is lowered slightly as well. This, in turn, prolongs the life of the nylon tube itself by putting less strain on it while it’s flapping around in the breeze. It’s kind of like how a flag flying in the breeze will last longer than one you fly on the back of your truck while you drive down the highway.

Summary:

Now that we’ve learned all this, what does it all mean? Well, going back to the nylon tube example, the tube itself is the CPU. So, all three properties discussed before come into play here around the nylon tube (CPU). The air pressure forces the wind up through the tube and causes the tube to raise in much the same way as the voltage from your battery causes the electrical current to flow along the circuits through the CPU. Wattage is simply the maximum amount of juice flowing from the battery keeping everything running at the same current.

All this nylon tube talk is only here to show you how the act of undervolting your CPU actually affects the processor itself. Yes, it does reduce stress on your CPU. Yes, it does reduce the drain on the battery. No, it will not likely produce a result that you’ve been hyped up to believe. The effects of undervolting your CPU are minimal at best, and should, in my opinion, only be used if you want your CPU to run a bit cooler under demanding tasks, such as using a heavy GPS app, like CoPilot, for a few hours, or while playing graphics intensive games for a while. Outside of that, you may gain about 30 minutes of extra run time on your battery on average (everyone’s phone is different, this is a rough average), or another couple of months of life on your CPU. Keep in mind that CPUs last many years on average under normal use, notwithstanding defects or abuse.

I’m certainly not telling you to avoid undervolting. I undervolt all my devices, including my personal computers. This post is meant to be informative since most people do this without understanding most of the concepts, while they buy into the hype generated around this. My main point is that the main reason you should undervolt is to keep the heat down on your device while you do demanding things. After all, you have a device in your hands today, most likely, that is more powerful than most desktop PCs just a few short years ago. Why wouldn’t you want to get everything out of it?

Bonus example:

Yet another example of voltage and amperage is your own cell phone charger. Most cell phone chargers now are 5V (volt), 1A (ampere/amp) chargers. This means that there are 5 volts pushing the 1 ampere electrical current to your phone over the USB cable. Wattage comes into play here in the electrical outlet. Most US electrical outlets are rated at 125 watts. Most cell phones are rated at 4-5W (watts) per hour. This means, that the outlet will still have a capacity of 120 or so watts per hour left over while your phone is charging.

How to undervolt:

The procedure for undervolting is different for each device (normally), so I’m not going to show anyone how to do it here. There are a few apps on the market that can help you do it if your kernel supports this feature. If you don’t know if your kernel supports this feature, please ask your ROM chef. Most, if not all, stock ROMs do not support this.

Apps:

The following apps will allow you to tweak your voltage settings if your kernel/ROM allow it. Root is required. There are many more on the market, but these are a few of the most popular ones.

System Tuner Pro

Set CPU

Voltage Control

IncrediControl