Thursday 4 January 2018

Not us! Android makers say they never slow phones over battery problems

Android phone makers are responding to Apple’s recent public relations nightmare, after it was revealed the company slowed older iPhone models down to compensate for aging batteries, and to avoid any problems that may occur due to them. Samsung, LG, HTC, and Motorola have all made statements saying they do not use similar tactics.
Motorola does not throttle processors inside its phones when the battery gets old, the company told The Verge, while HTC said something very similar. LG was even more forthcoming, saying it never has, and never will slow down processors inside its devices, because it, “cares what our customers think.”
Samsung issued a longer statement, saying that in addition to not slowing processors over time, it uses software and built-in safety features to “govern the battery-charging current and charging duration.” This suggests Samsung prefers to manage the battery as it starts to age, rather than temper the processor to reduce strain. We have contacted Huawei and OnePlus for comment, and will update when both respond.
While many will be pleased their Android phones won’t hit an artificial speed limit in the future, this doesn’t mean Android phones are immune to problems. The iPhone uses the same battery technology as every Android phone — therefore it degrades in the same way — and replacing the battery inside almost all flagship Android phones today is an equally awkward process, as well.
Reports of long-term system slowdown for Android phones aren’t rare either, and are usually caused by lack of storage space, memory fragmentation, or other system issues. Huawei is one company that has acknowledged this, and the company has made it very clear how it addresses the problem. Introduced in EMUI 5.0, it used machine learning to understand how you use your phone, then allocate resources intelligently to speed things up, along with new processes to manage memory. It promises EMUI 5 and above-equipped phones will remain fast even after 18 months of use.
Apple has responded to criticism by lowering the price of a replacement battery for the iPhone, which resolves any device throttling. Apple also went into detail about why it implemented these measures in the first place.

Install Computer’s Power Supply

Teach you how to replace your computer’s internal power supply component.
Step 1.Find the power supply.
This supplies power to the other components, which is why it has so many wires coming out of it. It is usually positioned at the back top corner of the computer case. The power supply has a fan built into it to keep itself and the computer cool.
Step 2.Get into the tower.
To get into the tower, you will have to remove the panel which is on the right hand side when viewing the tower from the back. Open this side of computer case by removing the screws at the back of the tower which are holding it in place. Then simply slide the panel off.
Step 3.Disconnect the power cables.
Cable from the power supply should be connected to each component requiring power. These cables are easy to disconnect simply pull out the plugs from sockets on the back of the components. The plug and socket on the motherboard are a different shape from the normal type, but it should come out just as easily. It may be a good idea to write down how many sockets were disconnected so you can make sure they are all reconnected later with the new unit.
Step 4.Remove the power supply.
Remove the screws at the back of the power supply unit while supporting it with one hand. Once the screws are undone it should be easy to slip the old unit out of the tower.
Step 5.Power cable connection.
Screw in new drive then connect the power cables to every component that was originally connected. Remember if any components are left unconnected they will not work.
Step 6.Get it going again.
Switch the computer on, if all the components have been connected you should be ready to go.
Q&A
My PSU is on the top front of my case. Can you help me to remove it? It comes with a case so it’s generic?
Check for screws on the outside of the case, and inside of it. See where the PSU is being held into the case. I cannot help that much as I do not know what case you have.

Wednesday 3 January 2018

All the Sensors in Your Smartphone, and How They Work

Your smartphone is a remarkable feat of engineering. It’s half a dozen or more gadgets packed into a single slab. Much of it’s coolest feats are accomplished with a wide range of sensors — but what are they and what do they all actually do?
How does your phone count your steps and replace your fitness tracker? Does GPS use up your data? Which sensors should you make sure are in your next handset?
Here’s all you need to know.
Accelerometer
Accelerometers handle axis-based motion sensing and can be found in fitness trackers as well as phones—they’re the reason why your smartphone can track your steps even if you haven’t bought a separate wearable.
They also tell the phone’s software which way the handset is pointing, something that’s becoming increasingly important with the arrival of augmented reality apps.
As the name kind of gives away, accelerometers measure acceleration, so the map inside Snapchat can put a cute toy car around your bitmoji when you’re driving, plus a host of other actually useful applications.
The sensor is itself made up of other sensors, including microscopic crystal structures that become stressed due to accelerative forces. The accelerometer then interprets the voltage coming from the crystals to figure out how fast your phone is moving and which direction it’s pointing in.
From switching apps from portrait to landscape, to showing your current speed in a driving app, the accelerometer is one of your phone’s most important sensors.
Gyroscope
The gyroscope helps the accelerometer out with understanding which way your phone is orientated— it adds another level of precision so those 360-degree photo spheres really look as impressive as possible.
Whenever you play a racing game on your phone and tilt the screen to steer, the gyroscope rather than the accelerometer is sensing what you’re doing, because you’re only applying small turns to the phone and not actually moving through space.
Gyroscopes aren’t exclusive to phones. They’re used in altimeters inside aircraft to determine altitude and position, for example, and to keep cameras steady on the move.
The gyroscopes inside phones don’t use wheels and gimbals like the traditional mechanical ones you might find in an old plane—instead they’re MEMS (Micro-Electro-Mechanical Systems) gyroscopes, a smaller version of the concept embedded on an electronics board so it can fit inside a phone.
The first time MEMS gyroscopes really hit it big was with the iPhone 4 in 2010. Back then, it was incredibly novel to have a phone that could detect orientation with such accuracy—nowadays, we take it for granted.
Magnetometer
Completing the triumvirate of sensors responsible for working out where a phone is in physical space is the magnetometer. Again the name gives it away—it measures magnetic fields and can thus tell you which way is north by varying its voltage output to the phone.
When you go in and out of compass mode in Apple Maps or Google Maps, that’s the magnetometer kicking in to work out which way up the map should be. It also powers standalone compass apps.
Magnetometers are found in metal detectors as well, as they can detect magnetic metals, which is why you can get metal detector apps for your smartphone.
However, the sensor doesn’t work alone for its primary purpose, which is inside mapping apps—it operates in tandem with the data coming from the phone’s accelerometer and GPS unit to figure out whereabouts you are in the world, and which way you’re pointing (very handy for those detailed navigation routes).
GPS
Ah, GPS—Global Positioning System technology—where would we be without you? Probably in a remote, muddy field, cursing the day we ditched our paper maps for the electronic equivalents.
GPS units inside phones gets a ping from a satellite up in space to figure out which part of the planet you’re standing on (or driving through). They don’t actually use any of your phone’s data, which is why you can still see your location when your phone has lost signal, even if the map tiles themselves are a blurry, low-res mess.
In fact, it connects with multiple satellites then calculates where you are based on the angles of intersection. If no satellites can be found—you’re indoors or the cloud cover is heavy—then you won’t be able to get a lock.
And while GPS doesn’t use up data, all this communicating and calculating can be a drain on your battery, which is why most battery-saving guides recommend switching GPS off. Smaller gadgets like most smartwatches don’t include it for the same reason.
GPS isn’t the only way your phone can work out where it is—distance to cell towers can also be used as a rough approximation, as Serial taught us—but if you’ve got some serious navigating to do then it’s essential. Modern-day GPS units inside smartphones actually combine GPS signals with other data, like cell signal strength, to get more accurate location readings.
The best of the rest
You’ve got plenty more sensors in your handset, though they’re perhaps not all as important as the four we’ve just mentioned. Many phones, including the iPhone, have a barometer that measures air pressure: it’s useful for everything from detecting weather changes to calculating the altitude you’re at.
The proximity sensor usually sits up near the top speaker and combines an infrared LED and light detector to work out when you have the phone up to your ear, so that screen can be switched off. The sensor emits a beam of light that gets bounced back, though it’s invisible to the human eye.
Meanwhile the ambient light sensor does exactly what you would expect, taking a measuring of the light in the room and adjusting your screen’s brightness accordingly (if indeed it’s set to auto-adjust).
Like the rest of the tech packed inside your handset, these sensors are getting smaller, smarter, and less power-hungry all the time, so just because phones five years apart both have GPS doesn’t mean they’re both going to be as accurate. Add in software tweaks and optimizations too and it’s more reason to upgrade your handset on a regular basis, even if you’ll almost never see these sensors listed on a specs sheet.

What Do the AI Chips in New Smartphones Actually Do?

Artificial intelligence is coming to your phone. The iPhone X has a Neural Engine as part of its A11 Bionic chip; the Huawei Kiri 970 chip has what’s called a Neural Processing Unit or NPU on it; and the Pixel 2 has a secret AI-powered imaging chip that just got activated. So what exactly are these next-gen chips designed to do?
As mobile chipsets have grown smaller and more sophisticated, they’ve started to take on more jobs and more different kinds of jobs. Case in point, integrated graphics—GPUs now sit alongside CPUs at the heart of high-end smartphones, handling all the heavy lifting for the visuals so the main processor can take a breather or get busy with something else.
The new breed of AI chips are very similar—only this time the designated tasks are recognizing pictures of your pets rather than rendering photo-realistic FPS backgrounds.
What we talk about when we talk about AI
AI, or artificial intelligence, means just that. The scope of the term tends to shift and evolve over time, but broadly speaking it’s anything where a machine can show human-style thought and reasoning.
A person hidden behind a screen operating levers on a mechanical robot is artificial intelligence in the broadest sense—of course today’s AI is way beyond that, but having a programmer code responses into a computer system is just a more advanced version of getting the same end result (a robot that acts like a human).
As for computer science and the smartphones in your pocket, here AI tends to be more narrowly defined. In particular it usually involves machine learning, the ability for a system to learn outside of its original programming, and deep learning, which is a type of machine learning that tries to mimic the human brain with many layers of computation. Those layers are called neural networks, based on the neural networks inside our heads.
So machine learning might be able to spot a spam message in your inbox based on spam it’s seen before, even if the characteristics of the incoming email weren’t originally coded into the filter—it’s learned what spam email is.
Deep learning is very similar, just more advanced and nuanced, and better at certain tasks, especially in computer vision—the “deep” bit means a whole lot more data, more layers, and smarter weighting. The most well-known example is being able to recognize what a dog looks like from a million pictures of dogs.
Plain old machine learning could do the same image recognition task, but it would take longer, need more manual coding, and not be as accurate, especially as the variety of images increased. With the help of today’s superpowered hardware, deep learning (a particular approach to machine learning, remember), is much better at the job.
To put it another way, a machine learning system would have to be told that cats had whiskers to be able to recognize cats. A deep learning system would work out that cats had whiskers on its own.
Bear in mind that an AI expert could write a volume of books on the concepts we’ve just covered in a couple of paragraphs, so we’ve had to simplify it, but those are the basic ideas you need to know.
AI chips on smartphones
As we said at the start, in essence, AI chips are doing exactly what GPU chips do, only for artificial intelligence rather than graphics—offering a separate space where calculations particularly important for machine learning and deep learning can be carried out. As with GPUs and 3D graphics, AI chips give the CPU time to focus on other tasks, and reduces battery draw at the same time. In also means your data is more secure, because less of it has to be sent off to the cloud for processing.
So what does this mean in the real world? It means image recognition and processing could be a lot faster. For instance, Huawei claims that its NPU can perform image recognition on 2,000 pictures every second, which the company also claims is 20 times faster than it would take with a standard CPU.
More specifically, it can perform 1.92 teraflops, or a trillion floating point operations per second, when working with 16-bit floating point numbers. As opposed to integers or whole numbers, floating point numbers—with decimal points—are crucial to the calculations running through the neural networks involved with deep learning.
Apple calls its AI chip, part of the A11 Bionic chip, the Neural Engine. Again, it’s dedicated to machine learning and deep learning tasks—recognizing your face, recognizing your voice, recording animojis, and recognizing what you’re trying to frame in the camera. It can handle some 600 billion operations per second, Apple claims.
App developers can tap into this through Core ML, and easy plug-and-play way of incorporating image recognition and other AI algorithms. Core ML doesn’t require the iPhone X to run, but the Neural Engine handles these types of tasks faster. As with the Huawei chip, the time spend offloading all this data processing to the cloud should be vastly reduced, theoretically improving performance and again lessening the strain on battery life.
And that’s really what these chips are about: Handling the specific types of programming tasks that machine learning, deep learning, and neural networks rely on, on the phone, faster than the CPU or GPU can manage. When Face ID works in a snap, you’ve likely got the Neural Engine to thank.
Is this the future? Will all smartphone inevitably come with dedicated AI chips in future? As the role of artificial intelligence on our handsets grows, the answer is likely yes. Qualcomm chips can already use specific parts of the CPU for specific AI tasks, and separate AI chips is the next step. Right now these chips are only being utilized for a small subsection of tasks, but their importance is going to only grow.

Tuesday 2 January 2018

6 ways to improve your laptop’s battery life on Windows 10

Don’t let your portable PC run out of power. Follow these tips and you’ll get a lot more battery life out of your Windows 10 machine.
Battery life is always a crucial part of any PC, whether it’s old or brand new.
We’ve already explained some techniques to preserve power on Windows 7 but what about Microsoft’s latest addition Windows 10? Thankfully if you’re using the new operating system, there are a number of simple tips that will help you save on power so you can continue using your PC that little bit longer. Watch the video below to see some of the tips in action and follow our guide for more details.
Tip 1: Turn off wi-fi and Bluetooth
Windows 10’s new Action Center makes it easier to switch off connectivity options such as wi-fi and Bluetooth which can drain battery life.
If you don’t need or Bluetooth on all the time, go to the Action Center by clicking the small square icon near the time in the bottom right, and click on Bluetooth to deactivate them so that they’re no longer lit. Older machines may not have Bluetooth, in which case you won’t see that option.
Wi-fi is usually used a lot of the time, but if you don’t need to be online for a while (perhaps if you’re writing a letter using a word processor) you can always click the Wi-fi icon to turn it off, which will save some battery as well.
Alternatively, if you want to switch all connectivity options off for a certain period of time, click Airplane mode and it’ll cut off all connections for you. When you want them back, simply click Airplane mode again.
Tip 2: Turn on Battery Saver
For laptops that aren’t plugged in to a power source, Windows 10’s new Battery Saver is a great way to preserve some of your machine’s juice.
Battery Saver does what its name suggests by reducing screen brightness, stopping push notifications and preventing apps from running in in the background.
Battery Saver is automatically set to kick in whenever your battery falls below 20%, but you can switch it on at any time (if mains power is not connected) from the Action Center.
You can also set Battery Saver to start automatically a bit earlier or later too, by going into the settings menu. Simply search for ‘Battery’ in Cortana and select Change battery saver settings at the bottom.
From here you can adjust the point at which Battery Saver will kick in by moving the scrolling bar.
Tip 3: Turn the sound down
Your PC’s speakers use up a decent amount of power, so turning them down even a little bit could help save some of your battery’s life.
Headphones also use less battery than speakers, so if you can opt for a pair instead, all the better.
Tip 4: Turn screen brightness down
The brightness of your screen is another big battery sucker. You can turn it down a notch or two by searching for ‘Brightness’ in Cortana and clicking on Display settings.
Under ‘Adjust brightness level’, move the scrolling bar down – but make sure it’s still bright enough to use.
Tip 5: Adjust power and sleep settings
Leaving your PC idle is a waste of battery, so make sure you’ve got the best screen and sleep options set-up.
Search ‘Power’ in Cortana and select Power & sleep settings.
Here, you can adjust how long your PC should wait before the screen dims or goes into sleep mode. Select a suitable time that you’re comfortable with from each drop down box.
Tip 6: Unplug any peripherals you’re not using
Got a USB stick plugged in all day but not using it? Remove it! Even if you’re not actively using it yourself, your PC will still be powering it.

Top tips for shooting video on your smartphone

The phone you carry around all day is also a brilliant video recorder. Here are some basic tips for mastering mobile video.
As Christmas draws closer, many of us will be taking photos and shooting videos on our phones.
Follow our shooting tips to make your home movies even better.
Shooting Tips
Record in landscape
Filming in portrait mode can seem natural because that’s generally how we hold and use our phones. But it’s no good if you want to share it on any online portal or cast it to your TV. That’s because you’ll get vertical black borders surrounding your thin-looking clip.
So shoot in landscape mode – holding the phone is on its side - is essential. You might have to stand a little further from your subject, but it gives you a wider angle to fit more of the scene in your shot.
Keep a steady hand
There’s nothing more distracting than wobbly video, motion blur and out-of-focus subjects. One way to steady your shot is to hold your phone with both hands.
It’ll help you cut the amount of movement - but take care not to cover the lens or the microphone by mistake.
Many high-end smartphones, like the Sony Xperia X, have stabilisation technology to help reduce shake.
Keep movement smooth
Capturing moving subjects isn’t easy. So you’ll need to keep your camera movements smooth. One way to do that is by moving your body rather than just your arms - keep your elbows locked to your side and rotate your body instead. Or try using a tripod.
Take care with zooming
The digital zoom on most smartphone video cameras enlarges the pixels, which can diminish the quality. So try not to use it unless you really need to.
If you can, get closer to your subject instead. The alternative is pixelated, noisy video you won’t want to watch anyway. Have you ever had to sit through a friends’ video shot at a concert? That’s  what you want to avoid.
Experiment to find the best light
It’s important to try to find the best light for your imagery, so move around and make use of natural light if possible. In daylight, try to make sure the sun is lighting your scene rather than shining directly into the lens.
Avoid the flashlight
On most phone cameras, the flash can double up as a light to illuminate subjects when recording video. But it can be too strong and make it look unnatural. So save it for when you can't find any natural light.
Manually adjust exposure and focus
Many smartphone cameras feature a tap to focus setting and a way to adjust the exposure (controlling how much light the sensor lets in). Both methods can help with lighting your subjects correctly.
On an iPhone, for example, you can long press on the focal point to lock the focus and exposure.
Use the time lapse setting
Most high-end smartphones now have a time lapse setting, which lets you condense several minutes or even hours of footage in to a much shorter clip. This can be a great way to capture interesting road trips, tidal scenes or sunrises and sunsets. Here it’s important to lock the exposure (as we explained above) to make sure the lighting stays consistent.
Protect yourself from the elements
If it’s possible you should use your body to shield your phone from the wind, because it’ll ruin the audio. Position yourself in a way that stops the breeze getting to your phone’s microphone at the bottom of the handset.
Practical tips for your smartphone
Shoot at lower quality
4K and Ultra HD video are becoming more common on our phones. Which is great, but the resulting clips take up much more space on your phone. You can save space by shooting at lower quality.
Don’t eat up all your data
Upload large video files over wi-fi so you don’t use up all your mobile data allowance.
Trim your footage
Most phone cameras offer the ability to whip off the awkward start and end of clips, giving the video a more professional feel.
Use an editing app
You can use a specialised editing app to pull more than one clip together. Many will also let you add fades and transitions as well as a soundtrack. Try Apple’s own iMovie for iOS and KineMaster for Android.
Bring a spare battery
Shooting video does as much to drain battery life as any activity, so come prepared. If your phone has a removable battery, bring a spare. Otherwise, think about investing in a portable battery pack. 

Monday 1 January 2018

How to Use iPhone Low Power Mode for Longer Battery Life

Squeezing the longest use out of your iPhone battery is crucial. There are dozens of tips and tricks to help you, but if your battery is very low right now or you won't be able to charge for a while, here's one simple tip to conserve battery life: turn on Low Power Mode.
Low Power Mode is a feature of iOS 9 and up that disables some features of the iPhone in order to make your battery last longer.
How Much Extra Time Does Low Power Mode Get You?
The amount of extra battery life Low Power Mode delivers is dependent on how you use your iPhone, so there's no single prediction.
According to Apple, though, the average person can expect to up to get an extra 3 hours of battery life.
How to Turn On iPhone Low Power Mode
Sound like something you want to try? To turn Low Power Mode on:
1.     Tap the Settings app to open it.
2.     Tap Battery.
3.     Move the Low Power Mode slider to On/green.
To turn it off, just repeat these steps and move the slider of Off/white.
This isn't the only way to enable Low Power Mode, though. The iPhone gives you other options:
Ÿ   Siri—Just tell Siri "turn on Low Power Mode" (or a variation of that phrase) and she'll take care of it for you.
Ÿ   Pop-up Window—When your iPhone's battery life drops to 20%, and then again at 10%, the iOS displays a pop-up warning. In that warning is a button that can turn on Low Power Mode. Tap it to start saving battery.
Ÿ   Control Center—In iOS 11 and up, you can add Low Power Mode to Control Center. Check out the section at the end of the article for more on this.
What Does Low Power Mode Turn Off?
Making your battery last longer sounds great, but you have to understand the trade-offs to know when it's the right choice. When Low Power Mode is enabled, here's how the iPhone changes:
Ÿ   Processing power is reduced—The speed of the iPhone's processor influences how much battery it uses. Low Power Mode reduces the performance of the processor and the graphics chip to conserve battery. This means your phone will be a little slower and might not perform as well in games and other graphics-intensive tasks.
Ÿ   Background App Refresh is disabled—Your iPhone learns how you use apps and automatically updates them around the times you use them to ensure that the latest data is always waiting for you. It's a cool feature, but it also requires battery life. Low Power Mode temporarily suspends this feature.
Ÿ   Email fetch is turned off—The iPhone can be set to periodically grab new email from your accounts. Low Power Mode turns this feature off and forces you to manually check for new messages (open Mail and swipe down from the top on any inbox to refresh).
Ÿ   Automatic downloads are disabled—You can set your iPhone to automatically download app updates or purchases made on other devices. This keeps your content in sync, but it also requires power. Low Power Mode prevents automatic downloads while it's on.
Ÿ   Visual effects and animations are suspended—The iOS is packed full of all sorts of cool visual effects and animations. They make using the iPhone more fun, but they also use battery. By turning them off, Low Power Mode saves power.
Ÿ   Screen brightness is turned down—The brighter your phone's screen, the more battery you use. Low Power Mode reduces your screen brightness to save energy.
Can You Use Low Power Mode All the Time?
Given that Low Power Mode can give your iPhone up to 3 hours of extra battery life, and the features it turns off aren't completely essential to using the phone, you may wonder if it makes sense to use all the time.
Writer Matt Birchler tested that scenario and found that Low Power Mode can reduce battery use by 33%-47% in some cases. That's a huge savings.
So, if you don't use the features listed above very much, or are willing to give them up for more juice in your battery, you could use Low Power Mode all the time.
When Low Power Mode Is Automatically Disabled
Even if you've turned on Low Power Mode, it's automatically turned off when the charge in your battery exceeds 80%.
Adding a Low Power Mode Shortcut to iOS 11 Control Center
In iOS 11 and up, you can customize the options that are available in Control Center.
One of the changes you can make is to add Low Power Mode. If you do this, turning the mode on is as simple as opening Control Center and tapping a button. Here's how to do that:
1.     Tap Settings.
2.     Tap Control Center.
3.     Tap Customize Controls.
4.     Tap the green + icon next to Low Power Mode. It will move into the Include group at the top.
5.     Open Control Center and the battery icon at the bottom of the screen toggles Low Power Mode on and off.

Computer Power Supply Wattage

Pretty much every power supply on the market for a desktop PC computer is advertised solely on its wattage. Unfortunately, this is a simplistic view of a very complex issue. The power supply is there to convert the high voltage from the wall outlet into the lower voltages required to operate the computer circuitry. If this is not done properly, the irregular power signals that are sent to the components can cause damage and system instability.
Because of this, it is important to make sure you buy a power supply that meets the needs of your computer system.
Peak vs. Maximum Wattage Output
This is the first real big gotcha when it comes to looking at power supply specifications. The peak output rating is the highest amount of power the unit can supply but this is only for a very brief time. Units cannot continuously supply power at this level and if it attempts to do so will cause damage. You want to find the maximum continuous wattage rating of the power supply. This is the highest amount that the unit can supply stably to the components. Even with this, you want to make sure the maximum wattage rating is higher than you intend to use.
Another thing to be aware of with the wattage output has to do with how it is calculated. There are three primary voltage rails inside of the power supply: +3.3V, +5V and +12V. Each of these supplies power to the various components of the computer system.
It is the combined total power output of all these lines that make up the total power output of the power supply. The formula used to do this is:
Ÿ   Wattage = Voltage * Amperage
So, if you look at a power supply label and it shows that the +12V line supplies 18A of power, that voltage rail can supply a maximum of 216W of power.
This may be only a small fraction of say the 450W the power supply is rated at. The maximum output of the +5V and +3.3V rails would then be calculated and added to the overall wattage rating.
+12V Rail
The most important voltage rail in a power supply is the +12V rail. This voltage rail supplies power to the most demanding components including the processor, drives, cooling fans and graphics cards. All of these items draw a lot of current and as a result you want to make sure that you purchase a unit that supplies enough power to the +12V rail.
With the increasing demands on the 12V lines, many new power supplies have multiple 12V rails that will be listed as +12V1, +12V2 and +12V3 depending on if it has two or three rails. When calculating the amps for the +12V line, it is necessary to look at the total amps produces from all of the 12V rails. Often times there might be a footnote that the combine maximum wattage will be less than the total rating of the rails. Just reverse the above formula to get the maximum combined amps.
Ÿ   Amperage = Wattage / Voltage
With this information about the +12V rails, one can use it against a general power usage based on the system of the system. Here are the recommendations for the minimum combined 12V rail amperages (and their relative PSU wattage rating) for various size computer systems:
Ÿ   Small Form Factor - 15A (250W)
Ÿ   Mini-Tower - 25A (300-350W)
Ÿ   Mid-Tower - 35A (400-500W)
Ÿ   Full Tower - 40A (600-650W)
Ÿ   Dual Video Card (SLI) - 50A (750W+)
Remember that these are only a recommendation. If you have specific power hungry components, check the power supply requirements with the manufacturer. Many high end graphics cards can pull near 200W on their own under full load. Running two of the cards can easily require a power supply that can sustain at least 750W or more of total power output.
Can My Computer Handle This?
I frequently get questions from people who are looking to upgrade their graphics card in their desktop computer system.
Many high-end graphics cards have very specific requirements for power in order to operate properly. Thankfully this has improved with manufacturers now listing some information. Most will just list the recommended total wattage of the power supply but the best is when they list the minimum number of amps required on the 12V line. Previously they never published any power supply requirements.
Now, in terms of most desktop computers, the companies generally do not list the PC's power supply ratings in their specifications. Typically the user will have to open up the case and look for the power supply label to determine what exactly the system can support. Unfortunately, most desktop PCs will come with fairly low power supplies as cost savings measures. A typical desktop PC that didn't come with a dedicated graphics card will usually have between a 300 to 350W unit with around 15 to 22A rating. This will be fine for some budget graphics cards, but many of the budget graphics cards have been increasing in their power demands where they won't work.
Conclusions
Remember that everything we have been talking about involves the maximum limits of the computer power supply. Probably 99% of the time a computer is being used, it is not being used to its maximum potential and as a result will draw much less power than the maximums. The important thing is that the computer power supply needs to have enough headroom for those times that the system is being taxed heavily. Examples of such times are playing graphic intensive 3D games or doing video transcoding.
These things heavily tax the components and need additional power.
As a case in point, I put a power usage meter between the power supply and the wall outlet on my computer as a test. During average computing, my system was pulling no more than 240W of power. This is well below the rating of my power supply. However, if I then play a 3D game for several hours, the power usage peaks upwards to around 400W of total power. Does this mean that a 400W power supply would be sufficient? Probably not as I have a large number of items that draw heavily on the 12V rail such that a 400W could have voltage problems which would result in system instability.

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