UCS Transformation Format—32-bit (UTF-32) is the trivial 32-bit Unicode character encoding. It encodes a sequence of Unicode code points in a sequence of 32-bit integers. There is a one-to-one mapping of Unicode code points to 32-bit values, so all characters require the same number of bits. Since the largest code points can be expressed in only 21 bits, this encoding is inherently wasteful of space; UTF-8 or UTF-16 is a more efficient coding in most cases. UTF-32 does provide computational simplicity and is more often used for in-memory storage of characters than for stored documents.
UTF-32 is also known as UCS-4. There may be some subtle philosophical differences between the terms "UTF-32" and "UCS-4", but for all practical purposes they are synonyms.
As with UTF-16, this format exists in both big- and small-endian varieties; since the relevant units are 32-bit chunks (not pairs of 16-bit chunks as the longer sequences of UTF-16 are), the endianness is applied to the entire 32 bits (4 bytes), meaning that the Byte Order Mark (zero-width no-break space) U+FEFF is encoded as byte sequence 00 00 FE FF in the big-endian version and FF FE 00 00 in the little-endian one (with all four bytes reversed from one version to the other). IANA has assigned the charset identifiers UTF-32BE (MIBenum 1018) and UTF-32LE (MIBenum 1019) to these variants.