why vista doesn't support 4GB RAM ?

By fxcm
in Microsoft (Windows)

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nautiqueskier

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lol pretty much everyone got this wrong.

a 32-bit OS has a 4GB address space which has to include RAM, any Memory on the Video Card, as well as space for device mappings and such.

So lets say you had a 768MB Nvidia 8800GTX video card (which are freaking expensive right now but w/e). Immediately 768MB of your 4GB goes to your video card. Then another probably 256-512MB goes to device mappings and such. And instantly Windows has less than 3GB of address space left to use for RAM.

Obviously 64-bit overcomes this limitation (you can go up into the terabytes if you'd like, although I think Microsoft software limits it).

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UncleSpellbinder

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  fxcm said:
All right thanks a lot. i am going install 64 bit vista now .

Best way to go, it seems. From the link posted above in post #5 by bangbang023:

  Quote
For Windows Vista to use all 4 GB of memory on a computer that has 4 GB of memory installed, the computer must meet the following requirements:

? The chipset must support at least 8 GB of address space. Chipsets that have this capability include the following:

? Intel 975X

? Intel P965

? Intel 955X on Socket 775

? Chipsets that support AMD processors that use socket F, socket 940, socket 939, or socket AM2. These chipsets include any AMD socket and CPU combination in which the memory controller resides in the CPU.

? The CPU must support the x64 instruction set. The AMD64 CPU and the Intel EM64T CPU support this instruction set.

? The BIOS must support the memory remapping feature. The memory remapping feature allows for the segment of system memory that was previously overwritten by the Peripheral Component Interconnect (PCI) configuration space to be remapped above the 4 GB address line. This feature must be enabled in the BIOS configuration utility on the computer. View your computer product documentation for instructions that explain how to enable this feature. Many consumer-oriented computers may not support the memory remapping feature. No standard terminology is used in documentation or in BIOS configuration utilities for this feature. Therefore, you may have to read the descriptions of the various BIOS configuration settings that are available to determine whether any of the settings enable the memory remappiAn x64 (64-bit) version of Windows Vista must be used.ust be used.

Contact the computer vendor to determine whether your computer meets these requirements.

Note When the physical RAM that is installed on a computer equals the address space that is supported by the chipset, the total system memory that is available to the operating system is always less than the physical RAM that is installed. For example, consider a computer that has an Intel 975X chipset that supports 8 GB of address space. If you install 8 GB of RAM, the system memory that is available to the operating system will be reduced by the PCI configuration requirements. In this scenario, PCI configuration requirements reduce the memory that is available to the operating system by an amount that is between approximately 200 MB and approximately 1 GB. The reduction depends on the configuration.

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Julius Caro

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  bangbang023 said:

That explanation is very logical and it is in accordance to what I'm being taught in computer science :p I was never told how 32 bit systems can address more than 4gb though, or how they can have 4GB ram while kepping the mapped I/O adresses

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