Computer storage units can be confusing, so here's a quick rundown:

-bits (e.g., megabits, gigabits)

• represented by kb, Mb, Gb, Tb, Pb, etc.
• mostly used for network bandwidth (e.g., Mbps) and bitrate (like audio and video files)

-bytes (e.g., megabytes, gigabytes)

• represented by kB, MB, GB, TB, PB, etc.
• used by manufacturers to represent hard drive and RAM size
• also used for network transfers (e.g., MB/s)

-bibytes (e.g., mebibytes, gibibytes)

• represented by KiB, MiB, GiB, TiB, PiB, etc.
• used by Windows for disks and files, though erroneously labelled MB, GB, etc. in Explorer — that's why a 4 TB hard drive will display as 3.63 TB in Windows