[sidewndr46]

No it isn't. The 64-bit capabilities of modern CPUs have almost nothing to do with memory. The address space is rarely 64 bits of physical address space anyways. A "64-bit" computer doesn't actually have the ability to deal with 64 bits of memory.

If you double the size of numbers, sure it takes up twice the space. If the total size is still less that one page it isn't likely to make a big difference anyways. What really makes a difference is trying to do 64-bit mathematics with 32-bit hardware. This implies some degree of emulation with a series of instructions, whereas a 64-bit CPU could execute that in 1 instruction. That 1 instruction very likely executes in less cycles than a series of other instructions. Otherwise no one would have bothered with it

[bombcar]

"Bitness" of a CPU almost always refers to memory addressing.

Now you could build a weird CPU that has "more memory" than it has addressable width (the 8086 is kind of like this with segmentation and 8/16 bit) but if your CPU is 64 bit you're likely not to use anything less than 64 bit math in general (though you can get some tricks with multiple adds of 32 bit numbers packed).

But a 32 bit CPU can do all sorts of things with larger numbers, it's just that moving them around may be more time-consuming. After all, that's basically what MMX and friends are.

[chasil]

The original 8087 implemented 80-bit operands in its stack.

It would also process binary-coded decimal integers, as well as floating point.

"The two came up with a revolutionary design with 64 bits of mantissa and 16 bits of exponent for the longest-format real number, with a stack architecture CPU and eight 80-bit stack registers, with a computationally rich instruction set."

https://en.wikipedia.org/wiki/Intel_8087

[comex]

Typically, it doesn't have the ability to deal with a full 64 bits of memory, but it does have the ability to deal with more than 32 bits of memory, and all pointers are 64 bits long for alignment reasons.

It's possible but rare for systems to have 64-bit GPRs but a 32-bit address space. Examples I can think of include the Nintendo 64 (MIPS; apparently commercial games rarely actually used the 64-bit instructions, so the console's name was pretty much a misnomer), some Apple Watch models (standard 64-bit ARM but with a compiler ABI that made pointers 32 bits to save memory), and the ill-fated x32 ABI on Linux (same thing but on x86-64).

That said, even "32-bit" CPUs usually have some kind of support for 64-bit floats (except for tiny embedded CPUs).

[monocasa]

The 360 and PS3 also ran like the N64. On PowerPC, 32 bit mode on a 64 bit processor just enables a 32 bit mask on effective addresses. All of the rest is still there line the upper halves of GPRs and the instructions like ldd.

[duped]

You misread my comment. I'm not saying that it limits the amount of memory, I'm saying that _using more memory has cost_.

> If the total size is still less that one page it isn't likely to make a big difference anyways

It makes a significant difference when you're optimizing around cache behavior and SIMD lanes.