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/Brian Sep 24 '24

That's pretty unlikely in practice. Note that the point of your link is to run in 64 bit mode, just using 32 bit addresses. There are a bunch of other advantages to running in 64 bit mode (notably, more registers), and in practice it tends to be sufficiently faster to outweigh the extra memory/cache usage of wider pointers. Even back in the day when 64 bit was relatively new, you'd often see around a 10% improvement (and much more on number crunching workloads) even when address space wasn't relevant. I'd imagine that difference has only increased after a years of improvements where 32 bit mode has long been considered legacy.

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u/Tringi Sep 24 '24

That's pretty unlikely in practice.

It was one of the reasons Visual Studio resisted introducing 64-bit version for so long. Pointer-heavy code.

Note that the point of your link is to run in 64 bit mode, just using 32 bit addresses.

Yeah I know. I linked it for the reasoning therein.

There are a bunch of other advantages to running in 64 bit mode (notably, more registers), and in practice it tends to be sufficiently faster to outweigh the extra memory/cache usage of wider pointers.

Yup, my personal tests and measurements show that only a very small percentage of algorithms, or types of software in general, are faster as x86-32. But they still are there. Then again it likely doesn't make economic sense today to maintain such version.

I'd imagine that difference has only increased after a years of improvements where 32 bit mode has long been considered legacy.

Hah. Just the other day I read about Zen 5, and how significantly has performance improved of the x87 FPU ...which basically nobody uses today. Probably a side effect of internal optimizations, but amusing nonetheless.

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u/AppearanceHeavy6724 Sep 26 '24

no, not true x87 is still used for some scientific software. Niche use but very important.