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Why does Windows only show about 3.5GB of my 4GB+ of RAM?

I see a lot of people claim that 32bit OS can only support up to 3GB RAM, and other people claim 3.25, while others claim 3.5, and others even claim 4GB (Which makes the most sense to me: 32^2 bytes = 4GB)

Can anyone provide a definitive answer with some logic to back up their statement? How much RAM can a 32bit OS support?

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    It's 4 GB but I am assuming depending on the machine and what else it needs memory for you can get different numbers displayed. See the answers here (superuser.com/questions/27086/…) – sealz Feb 23 '12 at 13:42
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    There's a very good answer to the similar question here. – tombull89 Feb 23 '12 at 13:44
  • Seems it is more of a Windows kernel limitation than a 32bit limit...unawave.de/windows-7-tipps/32-bit-ram-barrier.html?lang=EN – Moab Feb 23 '12 at 14:47
  • @Moab, I realise it was but as I found it through the "vote to close" dialogue and I read the question and answers for a couple of minutes before actually posting the comment. – tombull89 Feb 23 '12 at 15:09
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    @tombull89 that is why there is a delete button for comments – Moab Feb 23 '12 at 15:24

As a matter of theory, 2^32 is the max. However, each OS reserves different parts of the memory space for various things (kernel space, drivers, memory structures, etc) so the usable user space and sometimes reported RAM is less than the theoretical max.

  • Not sometimes. Every time. If you have 4GB or more in 32 Bit machines, you will NEVER see 4GB+ usable. it will always be three point something, depending on the system's needs. – Paperlantern Feb 23 '12 at 13:57
  • You are thinking Windows. My Linux boxes report exactly how much RAM they have. – uSlackr Feb 23 '12 at 18:02
  • Afraid not my friend. 32 bit is 32 bit. It is a physical limitation of the technology. It is not inherent to Windows only. Any 32 bit OS, regardless of race, creed, or color will only be able to address 4GB, less what the OS needs. Period. If you have a Linux distro that is seeing and allowing you to use more than 4GB, it is 64 Bit. I've heard of instances where systems will report installed memory, but its not the same as usable. – Paperlantern Feb 23 '12 at 19:04
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    According to Microsoft, most releases of Windows 7 (including 32-bit), support up to 192GB of RAM. The only requirement is that the underlying architecture is 64-bit. Can you please update your answer? – Dan Dascalescu Dec 30 '12 at 3:10
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    Chosen answer is WRONG. It hopelessly confuses virtual and physical addresses. 2^32, or 4 GB, is the max virtual address space. (the comments about "OS reserves different parts of the memory for various things..." are about v.a.s. as well.) But that's not RAM. Nearly all modern "32 bit" x86 CPUs are perfectly capable of addressing more than 4 GB RAM. For more detail, see my answer here: superuser.com/questions/1118924/… – Jamie Hanrahan Sep 1 '16 at 9:49

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