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A comment on What Every Programmer Should Know About Memory (2007) [pdf]. Parent comment

Re:What Every Programmer Should Know About Memory (2007) [pdf] by dragontamer on Monday March 04, 2019 @03:38PM (#19305149)
All pointers in user-space are 48-bits. All 48-bit pointers are translated by the page-directory virtual memory system into a real physical location.

There's an extension to use 55-bits or 56-bits... I forget exactly. But I don't think its actually been implemented yet on any CPU yet.

EDIT: It was Intel's 57-bit memory: https://en.wikipedia.org/wiki/Intel_5-level_paging . Yeah, I knew it was a weird number. But I guessed wrong earlier.

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Re:What Every Programmer Should Know About Memory (2007) [pdf] by bogomipz on Monday March 04, 2019 @05:07PM (#19306065)
Oh I see what you are saying but that's not really just a pointer or a userspace thing, that 48 bit limit is simply imposed by the x86-64 CPU vendors in no?

With 48 bits you can still address 256TB of memory. I guessing that from a practical and financial point of view it probably made little sense for vendors to build a CPU that enabled addressing the full 64 bits. At least for now.

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