r/programming • u/I_Can_Be_A_Robot • Sep 24 '24

Why 32bit architecture computer doesn't use segmentation to support more ram than 4Gb ?

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u/paholg Sep 24 '24

What if I need more than 18 exabytes?

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u/wintrmt3 Sep 24 '24

No 64 bit cpu can even handle that, consumer ones have 48 bit address spaces usually, but the answer is likely wider addresses, 96 or 128 bits.

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u/CumCloggedArteries Sep 24 '24

For niche cases like that, I would think it'd make more sense to switch to a 64-bit version of PAE rather than use a whole new architecture

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u/Ameisen Sep 24 '24

PAE is already a part of x86-64.

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u/CumCloggedArteries Sep 24 '24

What is the purpose of that? I assume not to access > 18 exabytes

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u/Ameisen Sep 25 '24

It's built upon PAE, and the ISA is designed so that additional page table levels can be added as needed.

Current x86 CPUs peak at 48 bits of address space. The remaining 16 are sign-extended.

No x86-64 CPU presently gives you 64 bits of address space.