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PC Technician explains memory in Windows 7

reported memory in windows 7
Why is the reported physical usable memory ( RAM) less than the actual installed memory in windows 7 ?

There is not a simple explanation for the difference. But I will try to summarize as best as possible. According to microsoft, the usable physical memory available for your computer is the total physical memory minus memory that is reserved by the hardware. For example, a video adapter that has 1 gig of onboard memory has this memory "mapped" to the computer's RAM memory thereby making this 1 gig of physical memory unavailable for the operating system and your applications. Another factor is the motherboard. The chipset on the motherboard must be able to support more address space ( probably by a factor of 2 ) than the total installed physical memory. A third factor is the version of windows 7 that is installed , ie , 32-bit or 64-bit. So if you install 4 GB of memory on a 32-bit version of windows 7 - it may report 3.5 GB of memory is available. Similarly, if you have 8 GB of memory installed on a 64-bit version - you may only see 7.1GB of usable memory. By the way, the upper limit for memory for the 32-bit version is 4 GB and ( even less for the "starter" version - 2 GB ) for the 64-bit version the limits can range as follows:

Window 7 - versions - Ultimate, Enterprise, Professional - 192 GB
Window 7 - Home Premium - 16 GB
WIndow 7 - Home Basic - 8 GB
So if you put more than 4GB of memory into a computer that is running the 32-bit version - you are just wasting money. As for the 64-bit, I would like to see a computer running 192 GB of memory and see how much is available for applications, which I guess, would need to be 64-bit apps. I am also curious about speed - if this much memory is available, you probably wouldn't need a page file - thereby eliminating the time consuming swapping to the page file ( hard disk access vs. memory access - no contest ). If I hit the lottery - I will try this experiment. You may have to wait a long time for the results, however. Now let's look at my windows 7 stats for memory usage( Windows 7 home premium edition) . These stats are found by going to Start => All Programs => Accessories => System Tools => System Information. Then click on System Summary - which displays this info on right hand side of page - at the bottom of the list.
memory stats on pc technician computer
Okay, the total memory installed is 3 GB - and the total physical memory is 2.75 GB this is because my video adapter is 256 MB or .25 GB. So 3 GB - 0.25GB is 2.75 GB as shown. But the next number shows 1.41 GB of physcial memory is available - this is because the other hardware devices map additional memory and the OS + background processes use memory for a total of 1.3 GB. The next number is probably not well labeled since this says "total virtual" memory - well this is not exactly all virtual memory, as this number is the sum of the page file size (2.75GB) and the total physical memory (total memory - video memory mapping = 2.75GB) which comes out to 5.5GB as shown. The available virtual memory of 3.93 GB is the sum of the page file size ( 2.75 GB) and the available physical memory ( 1.41 GB) which equals 4.16 GB - but this is not equal to 3.93GB as shown. Yes, this is true and I cannot figure out exactly where the missing memory went - but it is close enough not to worry about it.

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