GB (gigabyte) uses decimal (1,000³); GiB (gibibyte) uses binary (2³⁰ = 1,073,741,824). Hard drive manufacturers use decimal GB, so drives appear slightly smaller than advertised.
1 TB = 1,000 GB (decimal). In binary terms, 1 TB ≈ 931 GiB.
Mbps (megabits/second) measures internet speed; MB/s (megabytes/second) measures file transfer speed. 100 Mbps ≈ 12.5 MB/s.