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I'm using a 2 year old 15" AMD laptop running Windows 8, and its battery life is not as long as the brand new ultrabooks for sure.

In the place I'm currently working I don't have access to a power outlet, so I just purchased an extended battery from Ebay.

With proper brightness setting, power saving mode, periodic cleaning and turning off the unnecessary software I can have 4-5 hrs of juice.

Question: when I'm tracking software for system resource consumption I'm primarily focusing on CPU usage but I have no idea about the software with 0% CPU usage but relatively high memory usage. Should I try to keep my memory clean to have even more battery life?

PS: I have more than enough physical memory which is 8 GB so non-active software with memory consumption doesn't create extra burden for me in terms of performance.

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If you haven't already, go through Task Scheduler and make sure nothing you don't absolutely need is set to start while on battery. –  Daniel R Hicks Apr 8 at 12:00

6 Answers 6

Memory is a negligible factor, because it uses very little power (we're talking less than 3 watts per stick in a laptop).

And in fact, if you have a HDD, more memory usage would theoretically increase battery performance, because there is less HDD activity when memory is used as cache, instead.


The most power hungry components are ones that generate heat (CPU and GPU as they process information) and those that generate physical motion (the fans and any hard drives). Memory tends to generate relatively little heat (and obviously no physical motion).

The first steps I would take in increasing battery consumption would be to replace the HDD with an SSD, get a new battery and maybe replace the fans with those of better quality (harder to do on a laptop). Also abstain from any GPU or CPU intensive tasks. Any efforts beyond that are adding immeasurably small amounts of battery life.

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I'd be willing to bet that a memory stick takes a certain amount of juice to store and refresh it's contents, regardless of what those contents are -- but I'm not a RAM engineer. ;) –  Ƭᴇcʜιᴇ007 Apr 7 at 19:56
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@techie007 Yeah, but I bet it's a lot less than a spinning platter and and actuator :) –  Moses Apr 7 at 19:59
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@Spike An android phone doesn't have a hard drive, so freeing up the most widely used resource (flash memory) in that case would be beneficial. –  Moses Apr 8 at 2:32
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Apps thet free up memory also cause the termination of those apps. Android has hooks that allow it to suspend an app when memory gets full. Those apps are not brought back in until they are used again. That reduces CPU usage if those apps occasionally "check on things". –  Mark0978 Apr 8 at 3:26
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This answer is the correct answer for the OP. A more technically correct way to phrase the answer would be something like, Each memory module uses a mostly fixed amount of power. If you have 24GB of memory on your machine it will at all times use more power than an otherwise identical machine with only 8GB of memory. In the end though, memory is not a large power consumer on a laptop. The display and HDD are both beasts. –  krowe Apr 8 at 11:30

I'd agree with Moses' answer; more memory means less disk activity which means less power consumption.

I'd like to elaborate on the hardware however. There are many benchmarks like this one that show the small amounts of power involved. In that example, four 1.35V DDR3 SO-DIMM modules use 4 watts more under load than two modules (so about 2 watts per module, laptops typically have one or two). In any case, using memory alone is preferable to the power consumption of memory and hard drive combined.

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Note that that benchmark is measuring ECC RAM designed for server use. That does not necessarily translate to non-ECC laptop RAM. –  Bob Apr 8 at 9:47
    
"more available memory means less disk activity" does not make sense, and it's the opposite of the answer you say you're agreeing with. –  Andrew Medico Apr 8 at 14:53
    
@AndrewMedico In Windows "available" refers to the amount of memory that is not reserved or in use. Available memory is the sum of cached and free memory. Anything that is cached can become in use without accessing the hard drive. –  Jason Apr 8 at 15:27

No. Keeping memory "clean" is generally not necessary (though that doesn't mean one should waste it).

In its strictest sense, keeping memory "clean" may even be a very ill-advised idea. Although there exist so-called "memory optimizer" software where you pay for a program that keeps your memory "free" by purging filesystem caches, unloading DLLs, and trimming working sets, this kind of thing is snake oil.

RAM is meant to be used, if you keep RAM free, then you could as well have spent less money and bought less of it. In every modern operating system, memory pages that come from mappings are transparently migrated to and from the filesystem cache, which is not only much faster but also avoids disk activity. A disk typically consumes about twice as much power when active as compared to being idle. Your RAM consumes the same power either way (in theory, unused memory banks or unused memory modules could be powered down, but in practice this does not happen -- it would be most troublesome if one tried, insofar as physical memory is allocated and released in a pseudorandom way, so finding a complete module that's unused would be a daunting endeavor).
Bringing a program that is already running to the front is obviously faster and more power efficient than loading its image from disk, loading shared libraries, fixing imports, relocating, and starting up. Likewise, pulling a document out of the cache is faster and more power efficient than loading it from disk.

As long as you don't plug in additional memory (which you aren't going to do, since you mentioned you already have "enough"), the power consumption will remain the same.

That said, running lots of programs that serve no particular purpose (not programs that you actually use, or vital system components) is useless, and needlessly takes away RAM that the computer could otherwise use in a meaningful way (for programs or buffers). There is still a difference between keeping RAM used and wasting RAM.

For example, running 10 instances of Google updater, Logitech updater, Adobe updater, Office Speed Loader, Adobe Speed Launcher and so on, all of which do nothing truly useful, will take away memory that the OS could otherwise utilize as filesystem cache. While these programs may get paged out in presence of application need, this doesn't happen in favor of cache, and in any case it means needless writes to the swap file, even more so as they'll still have the occasional context switch despite "zero CPU", which would mean a page fault every time.
Thus, feel free to throw away stuff which isn't vital for the system's operation and which doesn't provide anything useful that you want. But don't blindly toss stuff just for ideology.

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Just a little more info to add to already nice answers.

  • Modern RAM sticks, sadly, very often fall into the heat generators category from the Moses' answer. Under load, that is.
  • Batteries wear out, some quicker and some slower. That usually accounts for decreased performance (and most certainly is the reason why you did buy a new one, I presume). Some laptop producers try to supply high quality battery assemblies, some aim for price only.
  • Battery replacement to be found at eBay are generally of worse quality than the original ones, very often eve if they are marked, branded and labelled as OEM or manufacturer original. These often wear out quicker as well. I had some 'original' battery packs for my ThinkPad bought from eBay and although they were not total rubbish, their performance was like that of real original after two years of heavy use.

Hope this helps.

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RAM doesn't generate nearly as much heat as a CPU or GPU. Sure, it feels warm to the touch, but that's typically without a fan or heatsink. Run a CPU without additional cooling and it'll be hot enough to burn you in a minute. Probably sooner. –  Bob Apr 8 at 9:49
    
@Bob: Off course CPU generates much more heat than RAM sticks, but that doesn't mean that heat energy generated by RAM sticks doesn't come from the laptop's battery, I'm sure you'll agree. And there are plenty of laptops out there whose memory can get or gets very hot indeed. –  Pavel Petrman Apr 8 at 11:10
    
The CPU and RAM are actually very similar in their efficiency. Both are silicon wafers. They function differently in that RAM will use the entire wafer at all times while a CPU will use certain pathways more often than others. This combined with the fact that you generally have several memory modules split up means that RAM will naturally dissipate heat better while a CPU will have 'hot spots'. The point of saying this is to clarify why heat alone isn't really telling you much with even slightly dissimilar devices unless you are very careful about how you measure that heat. –  krowe Apr 8 at 12:00

This is answered indirectly in the related question Does installing larger RAM means consuming more energy? and there are many details in the answers there. It's not technically a duplicate question, but they cover that same ground in the answers.

In practice, even at load, the increased consumption is negligible. If the RAM is being used to cache what would otherwise trigger disk or wifi access, the net power savings is enormous as it is deferring power from much more power hungry components.

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that's why modern OSes such as android or Vista and above caches frequently used programs and datas for faster loading instead of wasting space and energy for the remaining RAM –  Lưu Vĩnh Phúc Apr 8 at 2:57

From my understanding of your question, it doesn't matter if you're using 25% of 100% of your RAM; they power needed to keep the data in it is going to be the same.

RAM is considered as a volatile memory, since it needs to be refreshed very frequently (many times per second, in-between read/write cycles). This is why you lose everything that wasn't saved on disk when the power goes out.

This process of refreshing the RAM is done no matter if that part part of your RAM is in use or not.

So, an idle computer will not consume more power if it's RAM is used more; but as it is said in other answers, higher RAM usage likely mean more CPU usage to manage it; and "memory cleaners" are likely to consume more energy processing than leaving the Operating System do its job

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