The OS uses 1024 and the drive manufacturers are using 1000.
Which is why a 1TB drive shows 931GiB of capacity. (1024 GiB =1 TiB, 1024MiB =1 GiB, 1024KiB =1MiB, 1024 Bytes =1KiB) but the drive manufacturers using SI prefixes doing 1000 Bytes =1 KB, 1000 KB = 1MB, 1000MB = 1GB, 1000GB = 1TB.
Thus the discrepancy.

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