Data storage converter
Both families are listed separately: kilobytes, megabytes and gigabytes counting in thousands, and kibibytes, mebibytes and gibibytes counting in 1,024s. Mixing them is why a 1 TB drive shows up as 931 GB.
How to convert data sizes
The discrepancy is not a swindle, but it is a genuine ambiguity. Drive manufacturers use the SI meaning, where a terabyte is 10¹² bytes; Windows displays the same drive using 1,024-based arithmetic while still labelling it "GB", so 10¹² bytes reads as 931. Both numbers describe the same drive. The IEC introduced kibi, mebi and gibi in 1998 specifically to end this, and macOS and Linux now report in the SI sense — Windows is the main holdout. The other thing worth watching is bits versus bytes: network speeds are in bits per second, so a 100 Mbps connection downloads at about 12.5 MB/s at best.
Questions
The manufacturer counts a terabyte as 10¹² bytes; Windows divides by 1,024 three times while still writing "GB". Both describe the same drive.
A gigabyte is 10⁹ bytes; a gibibyte is 2³⁰, about 7.4 percent more. The IEC introduced the second set in 1998 to end the confusion.
No, a byte is eight bits. A 100 Mbps connection tops out around 12.5 MB/s.
The SI meaning since 10.6, so a drive shows the number on the box. Windows still uses 1,024-based arithmetic.
Because memory addressing is binary, so powers of two are the natural sizes. It was informally rounded to "kilo" and the habit stuck.