How Digital Storage Is Measured

Digital storage is measured in bytes, where one byte equals 8 bits and each bit is a binary 0 or 1. Units scale in two competing systems: SI (powers of 1,000) and binary (powers of 1,024). So 1 kilobyte (KB) = 1,000 bytes in SI, but 1 kibibyte (KiB) = 1,024 bytes in binary. This discrepancy is why a "500 GB" hard drive shows up as only about 465 GB in Windows — hard drive manufacturers use the larger-sounding SI definition, while operating systems historically counted in binary. Modern operating systems are gradually adopting the IEC binary prefixes (KiB, MiB, GiB) to reduce confusion.

What Fits in How Much Space?

To build intuition about data sizes: a plain text page is roughly 2 KB; a high-resolution JPEG photo runs 3–6 MB; a full hour of HD video needs 1–4 GB; the entire text-only content of English Wikipedia weighs about 21 GB; and the human genome (uncompressed) is approximately 3.2 GB. The estimated print collection of the Library of Congress is around 10 TB. A single petabyte (PB) = 1,000 TB — Google processes roughly 20 petabytes of data every day. Global internet traffic now exceeds 400 exabytes (400,000 petabytes) per year, and one zettabyte equals one billion terabytes.

Bits vs Bytes — the Speed Trap

One of the most common points of confusion is that internet connection speeds are measured in bits per second (Mbps), not bytes per second (MB/s). A 100 Mbps broadband connection actually downloads at about 12.5 MB/s — because there are 8 bits per byte. Always check whether a speed specification uses a lowercase b (bits) or uppercase B (bytes). Streaming a 4K film at around 25 Mbps uses roughly 3.1 MB per second, or about 11 GB per hour. Keeping this distinction in mind saves a lot of head-scratching when download speeds seem far slower than advertised.