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Windows Vista 32-bit recognizes 4GB of memory but only 3069MB?

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February 12, 2009 3:56:13 AM

Hi Guys,

So I'm a bit confused. I read in earlier posts that windows vista 32-bit only recognizes 3.5GB of ram. So I installed dual channel 2GBx2 Crucial RAM earlier today. When I right click on my computer to system properties, windows vista detects 4GB of RAM!!! However, when I open the task manager, my total physical memory is only 3069MB.

Can someone explain to me how to fix this?

Why does windows vista recognize 4GB of memory...can I use this full amount? Even if I am limited to 3.5GB of ram, why does task manager only show ~3GB RAM available?
February 12, 2009 4:22:58 AM

I'm a bit confused... layman terms? sorry :) 
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February 12, 2009 12:38:37 PM

laymans terms:

there's no fix. it works as designed. vista will "display" all 4GB of ram, but can only use about 3-3.5GB.
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February 12, 2009 12:41:10 PM

In a computer all bytes in the memory system need a unique name. This is called an address. For example, if you have 2 GB of main memory, then there are 2147483648 bytes of RAM in your machine, each of which require an address for the operating system to communicate to it. To give these all an address you need 31 bits to do it. Now, if/when you have 32 bits, you can name 4 GB (2 bytes to the 32nd power = 4GB).

This is why the total addressable space available in a 32 bit OS is 4GB – the OS runs out of addresses and cannot communicate/locate any more bytes of memory because of that.

You may think ”Hey, 4GB of address space… 4GB of RAM… What’s the problem” The problem is that memory isn’t the only thing needing an address. If you install a total of 4GB worth of RAM, the system will detect/use/display less than 4GB of total memory because of address space allocation for other critical functions, such as:

- System BIOS (including motherboard, add-on cards, etc..)
- Motherboards resources
- Memory mapped I/O
- Configuration for AGP/PCI-Ex/PCI
- Other memory allocations for PCI devices

Different onboard devices and different add-on cards (devices) will result of different total memory size. e.g. more PCI cards installed will require more memory resources, resulting of less memory free for other uses.

This limitation applies to most chipsets & Windows XP/Vista 32-bit version operating systems. Again, this is a limitation of the Operating System not having enough address space to allocate to the system *and* the RAM. Not allocating address space to devices renders them inoperable. Not allocating addresses to RAM simply results in the unaddressed section not being used in an otherwise fully functional computer. Therefore the OS designers assign RAM last.

We can have long debates about mathematical fundamentals and discussions about why the original Windows designers couldn't allocate the full theoretical max of 36 bits of address space so that users today would be able to use more resource. But at the end of the day, the designers and engineers 'Didn't Then'. So we 'Can't Now'.


If you install a Windows operating system, and if more than 3GB memory is required for your system, then the below conditions must be met:

1. A memory controller which supports memory swap functionality is used. The latest chipsets like Intel 975X, 955X, Nvidia NF4 SLI Intel Edition, Nvidia NF4 SLI X16, AMD K8 and newer architectures can support the memory swap function.

2. Installation of Windows XP Pro X64 Ed. (64-bit), Windows Vista 64, or other OS which can provide more than 4GB worth of address space.



Note: Windows Vista 32bit SP1 will display the installed amount of RAM. This is a display change only.
February 12, 2009 12:42:20 PM

Basically take the ram on your video card that you have, subtract it from your system ram and that's what 32 bit is going to use.
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