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Comment by ribit | Hacker News Reader

Time Machine backups use filesystem snapshots with reference-counted copy-on-write blocks. The total file size can easily surpass the actual amount of storage capacity. The same problem exists with modern virtual memory implementations, where the sum of allocated memory accessible to every process can be larger than the amount of physical RAM in the system (shared memory pages, file-backed pages etc.)

This is not about sanity checks. The value is correct. This is about presenting information in a way that makes sense to the user.

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That was also my first thought, references, virtual memory, etc. But I insist the value is incorrect. The measurement units got mixed up. You cannot say X Tb (virtual space) of Y Tb (physical space). These are different units! I can see how Apple tried boasting some inflated numbers to impress users, just like they try to sell 8gb mbp saying it is same amount as the old 16gb.

By the principle of least surprise, the reasonable expectation is to show used disk size is less than total size. It is reasonable for both technical and nontechnical users.

Apple claims the use of 8GB on M chips is more efficient than Intel with 16GB, therefore needs less physical capacity to match functionality.

Remember AMD Athlon CPU versions? Athlon XP "Barton" 3200+, running at 2.2GHz was equivalent of an Intel running at 3.2GHz.

Unless they've figured out how to let you store two bits per bit, it's still obviously a dubious claim. My x86 desktops have also had zswap for a decade, so whatever magic fairy dust they have can't be that simple.

The magic fairy dust is "really fast NVME" and "really low latency memory access" which for most users makes the 8GB give a performance comparable to slower 16GB memory (and not need to read from disk).

That's about it. If you're doing anything other than regular web browsing and word processing it's not going to be the same as having 16GB. But I'm certain the average Mac user is not a developer, video editor, or other power user.

Like it or not, tech nerds are not the average consumer of Apple hardware.

The total real value is the amount that's relevant for the action of clearing space. And if the way the virtual space made to the real space was already known, then the operation could be effectively instantaneous. The implementation shows the two most useful (to the user) pieces of information available.

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