Why a '1 TB' Drive Shows Less Than 1,000 GB of Actual Space
Storage manufacturers typically advertise capacity using decimal units (1 TB = 1,000,000,000,000 bytes), while most operating systems report capacity using binary units (where 1 "TB" is actually 1,099,511,627,776 bytes) — because the binary unit represents a larger number of bytes per labeled unit, the same physical drive shows a smaller number of "TB" when measured the operating system's binary way, even though no storage capacity is actually missing.
This is one of the most common sources of confused or suspicious "missing storage" complaints, and it has a precise, well-understood technical explanation.
Decimal (manufacturer) counting
Storage manufacturers conventionally use the decimal (SI, powers-of-1000) definition: 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes, and so on, consistent with how the metric system generally works — a "1 TB" drive under this convention genuinely contains 1 trillion (1,000,000,000,000) bytes.
Binary (operating system) counting
Most operating systems instead calculate and display capacity using binary (powers-of-1024) units — 1 "KB" as 1,024 bytes, 1 "MB" as 1,024 × 1,024 bytes, and so on. Under this convention, each labeled unit represents more actual bytes, so the same physical drive (with the same actual number of bytes) is reported as a smaller number of these larger binary units.
Why this looks like missing storage but isn't
A drive advertised as 1 TB (decimal) contains exactly the number of bytes that implies — but an operating system reporting that same byte count using binary units shows a figure like "931 GB" instead of "1,000 GB," since the binary GB is a larger unit — no actual storage capacity is missing; it's purely a difference in which counting convention is used to label and display the same underlying byte count.