The 8:1 Ratio
A bit is a single 0 or 1 — the smallest unit of data. A byte is 8 bits. Network speeds are measured in bits per second (Mbps), but file sizes are measured in bytes (MB). That's why a '100 Mbps' connection downloads at about 12.5 MB/s: 100 ÷ 8.
Why Two Units
Telecom historically measured line capacity in bits per second because a bit is what the wire transmits. Storage counts in bytes because a byte holds one text character and is a more useful grouping for files. The naming overlap (megabit vs megabyte) causes endless confusion.
Reading the Abbreviations
| Abbreviation | Unit | Size |
|---|---|---|
| b | bit | 1 |
| B | byte | 8 bits |
| Mbps | megabits/s | 1,000,000 bits/s |
| MB/s | megabytes/s | 1,000,000 bytes/s |