MB, GB, TB: 1024 vs 1000, Bits vs Bytes Explained

1024 vs. 1000: binary and decimal prefixes

Computers count in binary, so it was natural to group bytes in powers of two: 2^10 = 1,024. Early engineers borrowed the metric prefix "kilo" for this 1,024 value, and the habit stuck up through mega, giga, and tera. Meanwhile the metric system defines kilo as exactly 1,000. Two systems, same-looking names, different numbers.

To end the confusion, standards bodies introduced binary prefixes: kibibyte (KiB) = 1,024 bytes, mebibyte (MiB) = 1,024 KiB, gibibyte (GiB), and tebibyte (TiB). Under this scheme, "kilobyte" (KB) means exactly 1,000 bytes and "kibibyte" means 1,024. The gap grows with each step: at the tera level, 1 TB and 1 TiB differ by about 10%.

Bits vs. bytes: the factor of 8

A bit is a single 0 or 1; a byte is a group of 8 bits. The convention is that a lowercase "b" means bits and an uppercase "B" means bytes, so Mb is megabits and MB is megabytes. Storage is measured in bytes, but network and connection speeds are usually quoted in bits per second, which trips people up constantly.

The practical consequence: divide a connection's megabit figure by 8 to estimate real download speed in megabytes. A 100 Mbps line downloads at about 12.5 MB/s, so a 1 GB file takes roughly 80 seconds at full speed. Multiply by 8 to go the other way — a 25 MB/s transfer is a 200 Mbps stream.

Real file and storage sizes

Some anchors help. A plain text page is a few kilobytes; a high-quality photo is 3–8 MB; a song is about 5–10 MB; an hour of streamed HD video is roughly 3 GB. A dual-layer Blu-ray holds 50 GB, and a modern laptop SSD is commonly 512 GB or 1 TB. One terabyte, in decimal terms, is a trillion bytes — enough for roughly 250,000 photos.

This is why a "1 TB" drive shows less. The maker counts 1 TB as 1,000,000,000,000 decimal bytes, but the operating system divides by 1,024 three times to display gibibytes, giving 1,000,000,000,000 ÷ 1,024³ ≈ 931 GB. No storage went missing; the two sides just used different-sized gigabytes.

Frequently asked questions

Why does my 1 TB drive show only 931 GB?

The maker uses decimal 1 TB = 1,000,000,000,000 bytes, but your OS divides by 1,024 to show gibibytes, which gives about 931. No space is lost; the units differ.

What is the difference between a bit and a byte?

A bit is a single binary digit (0 or 1); a byte is 8 bits. Lowercase b means bits, uppercase B means bytes, so 8 Mb equals 1 MB.

How fast can I download on a 100 Mbps connection?

Divide by 8: 100 Mbps is about 12.5 MB/s, so a 1 GB file takes roughly 80 seconds at full speed, before real-world overhead.

Should I use MB or MiB?

Use MiB (1,024-based) when you mean binary units precisely, as many operating systems do internally. Use MB (1,000-based) for decimal counts like drive marketing. Stating which you mean avoids the 1024-vs-1000 confusion.