Bits and Bytes

Updated: 2021-12-07

Bit vs Byte

  • bit: a single 0 or 1. 2 different values. The most basic unit of computing
  • byte: 1 byte = 8 bits = 2 hex = 256 different values. A.k.a "octet". Still "naked" 0s and 1s, can be interpreted in different ways.
  • characters:
    • historically, 1 byte (8 bits) is used to encode a single character: ASCII uses 7 bits, 128 code points, more than enough for English characters (both lowercase and uppercase). One extra bit can be used as a parity bit.
    • now one character may need more than one byte to store, depend on the encoding.

Multiple-byte Units

Unit Abbrev. Bytes Unit Abbrev. Bytes
kB kilobyte 1000 KiB kibibyte 1024
MB megabyte 10002 MiB mebibyte 10242
GB gigabyte 10003 GiB gibibyte 10243
TB terabyte 10004 TiB tebibyte 10244
PB petabyte 10005 PiB pebibyte 10245
EB exabyte 10006 EiB exbibyte 10246
ZB zettabyte 10007 ZiB zebibyte 10247
YB yottabyte 10008 YiB yobibyte 10248

Note if there's an i in the unit name: with an i, it is binary, otherwise decimal.

For example:

  • terabyte (TB): 1012, or 10004, or 1,000,000,000,000 bytes
  • tebibyte (TiB): 240, or 10244, or 1,099,511,627,776 bytes, roughly 1TiB = 1.1TB

Real world examples

  • 3.5 inch Floppy Disk: 1,440 KiB = 1.47 MB = 1.41 MiB
  • CD: up to 700 MB
  • DVD: 4.7 GB = 4.38 GiB for a single-layered, single-sided disc
  • Blu-ray: 25 GB for single-layer
  • The Complete Works of William Shakespeare would occupy about 5,600,000 bytes when written in plain text without formatting.