Available/stand by/Free/cached memory. What are the differences?

I built a new computer about two months ago (running Win 7). It's stable except using an incompatible RAM in the beginning.

However, I don't understand the difference between Available/Standby/Free/cached memory. The free memory always stay low unless the system is on for a long-enough period of time. I usually don't have problems unless I'm trying to edit photos.

If I have low Available memory for the most part before it goes up, does that mean I need more RAM? I'm running Athlon II X4 630/2x2GB Cosair Dominator XMS3 DDR3 1333/M4A785TD-V EVO/Win 7 64.

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  1. Best answer
    Free – This one is quite simple. This memory has nothing at all in it. It’s not being used and it contains nothing but 0s.

    Available – This numbers includes all physical memory which is immediately available for use by applications. It wholly includes the Free number, but also includes most of the Cached number. Specifically, it includes pages on what is called the “standby list.” These are pages holding cached data which can be discarded, allowing the page to be zeroed and given to an application to use.

    Cached – Here things get a little more confusing. This number does not include the Free portion of memory. And yet imight see that it is larger than the Available area of memory. That’s because Cached includes cache pages on both the “standby list” and what is called the “modified list.” Cache pages on the modified list have been altered in memory. No process has specifically asked for this data to be in memory, it is merely there as a consequence of caching. Therefore it can be written to disk at any time (not to the page file, but to its original file location) and reused. However, since this involves I/O, it is not considered to be “Available” memory.

    Total – This is the total amount of physical memory available to Windows.

    You can go here -> to get more information on the memory readings. The guy even goes into giving you formulas to determine how much of the physical memory is actually in use, etc.

    For most people, 4 gigs is plenty for Windows 7. What exactly do you use your machine for? If it's just for day-to-day operations (surfing, email, word processing, gaming), do you find the hard drive is thrashing a lot? If so, then you're memory is being used and the OS is having to swap out to the hard drive. If that is the case, then I would look into seeing what services you have running and look for any runaway processes.

    However, if your system is not swapping out and the machine seems responsive, then you should be good. I would say a lot of the memory is being held as ready for use or cached. As long as you're not swapping out to the hard drive and the machine is responsive, then you should be fine.

    Also, have you tried running memory diagnostics to ensure that your memory is functioning properly?
  2. I haven't tried to run memory diagnostics, but I had a case where the memory I first bought for this system was not compatible with my setup.

    I use the computer for day-to-day operations and photo editing.

    Can you explain what "HDD is thrashing a lot"? For processes under "Process" tab in task manager, there's about 13 processes at the moment I get into desktop. Not sure how can I tell if the system is swapping out. But at least the system is responsive 99.9% of the tiime.
  3. What I meant is your hard drive light is constantly on and you can hear your hard drive thrashing as the OS writes out unused data to the swap file on your disk. If this is happening a lot, then it's a sure sign of your memory being eaten up by a run away process.

    Considering you have 4 gigs of memory, you shouldn't really be swapping out unless you're doing a lot of memory intensive operations with multiple programs running.

    Otherwise, if you aren't swapping out, then I would say you should be good to go.
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