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Disk Size and Usage Information

If your software needs to report disk size or usage information, it’s important to provide accurate values that are consistent with values reported by the Finder and other system applications, such as Activity Monitor. To do this, be sure to calculate all disk size statistics using GB, not GiB.

Briefly, a GB is defined as 1,000,000,000 bytes, whereas a GiB is defined as 1,073,741,824 bytes (which is the value of 2³⁰). Using GB instead of GiB to calculate disk sizes avoids confusing users with values that differ from the system-provided ones.