The overall format of the term format is as follows:

The compressed term format is as follows:

Uncompressed size (unsigned 32-bit integer in big-endian byte order) is the size of the data before it was compressed. The compressed data has the following format when it has been expanded:

Refers to the atom with AtomCacheReferenceIndex in the distribution header.

Unsigned 8-bit integer.

Signed 32-bit integer in big-endian format (that is, MSB first).

A float is stored in string format. The format used in sprintf to format the float is "%.20e" (there are more bytes allocated than necessary). To unpack the float, use sscanf with format "%lf".

This term is used in minor version 0 of the external format; it has been superseded by NEW_FLOAT_EXT.

An atom is stored with a 2 byte unsigned length in big-endian order, followed by Len numbers of 8-bit Latin-1 characters that forms the AtomName. The maximum allowed value for Len is 255.

Encodes a reference object (an object generated with erlang:make_ref/0). The Node term is an encoded atom, that is, ATOM_EXT, SMALL_ATOM_EXT, or ATOM_CACHE_REF. The ID field contains a big-endian unsigned integer, but is to be regarded as uninterpreted data, as this field is node-specific. Creation is a byte containing a node serial number, which makes it possible to separate old (crashed) nodes from a new one.

In ID, only 18 bits are significant; the rest are to be 0. In Creation, only two bits are significant; the rest are to be 0. See NEW_REFERENCE_EXT.

Encodes a port object (obtained from erlang:open_port/2). The ID is a node-specific identifier for a local port. Port operations are not allowed across node boundaries. The Creation works just like in REFERENCE_EXT.

Encodes a process identifier object (obtained from erlang:spawn/3 or friends). The ID and Creation fields works just like in REFERENCE_EXT, while the Serial field is used to improve safety. In ID, only 15 bits are significant; the rest are to be 0.

Encodes a tuple. The Arity field is an unsigned byte that determines how many elements that follows in section Elements.

Same as SMALL_TUPLE_EXT except that Arity is an unsigned 4 byte integer in big-endian format.

Encodes a map. The Arity field is an unsigned 4 byte integer in big-endian format that determines the number of key-value pairs in the map. Key and value pairs (Ki => Vi) are encoded in section Pairs in the following order: K1, V1, K2, V2,..., Kn, Vn. Duplicate keys are not allowed within the same map.

As from Erlang/OTP 17.0

The representation for an empty list, that is, the Erlang syntax [].

String does not have a corresponding Erlang representation, but is an optimization for sending lists of bytes (integer in the range 0-255) more efficiently over the distribution. As field Length is an unsigned 2 byte integer (big-endian), implementations must ensure that lists longer than 65535 elements are encoded as LIST_EXT.

Length is the number of elements that follows in section Elements. Tail is the final tail of the list; it is NIL_EXT for a proper list, but can be any type if the list is improper (for example, [a|b]).

Binaries are generated with bit syntax expression or with erlang:list_to_binary/1, erlang:term_to_binary/1, or as input from binary ports. The Len length field is an unsigned 4 byte integer (big-endian).

Bignums are stored in unary form with a Sign byte, that is, 0 if the binum is positive and 1 if it is negative. The digits are stored with the least significant byte stored first. To calculate the integer, the following formula can be used:

B = 256
(d0*B^0 + d1*B^1 + d2*B^2 + ... d(N-1)*B^(n-1))

Same as SMALL_BIG_EXT except that the length field is an unsigned 4 byte integer.

Node and Creation are as in REFERENCE_EXT.

ID contains a sequence of big-endian unsigned integers (4 bytes each, so N' is a multiple of 4), but is to be regarded as uninterpreted data.

N' = 4 * Len.

In the first word (4 bytes) of ID, only 18 bits are significant, the rest are to be 0. In Creation, only two bits are significant, the rest are to be 0.

NEW_REFERENCE_EXT was introduced with distribution version 4. In version 4, N' is to be at most 12.

See REFERENCE_EXT.

An atom is stored with a 1 byte unsigned length, followed by Len numbers of 8-bit Latin-1 characters that forms the AtomName. Longer atoms can be represented by ATOM_EXT.

This is the new encoding of internal funs: fun F/A and fun(Arg1,..) -> ... end.

This term is the encoding for external funs: fun M:F/A.

Module and Function are atoms (encoded using ATOM_EXT, SMALL_ATOM_EXT, or ATOM_CACHE_REF).

Arity is an integer encoded using SMALL_INTEGER_EXT.

This term represents a bitstring whose length in bits does not have to be a multiple of 8. The Len field is an unsigned 4 byte integer (big-endian). The Bits field is the number of bits (1-8) that are used in the last byte in the data field, counting from the most significant bit to the least significant.

A float is stored as 8 bytes in big-endian IEEE format.

This term is used in minor version 1 of the external format.

An atom is stored with a 2 byte unsigned length in big-endian order, followed by Len bytes containing the AtomName encoded in UTF-8.

For more information on encoding of atoms, see the note on UTF-8 encoded atoms in the beginning of this section.

An atom is stored with a 1 byte unsigned length, followed by Len bytes containing the AtomName encoded in UTF-8. Longer atoms encoded in UTF-8 can be represented using ATOM_UTF8_EXT.

For more information on encoding of atoms, see the note on UTF-8 encoded atoms in the beginning of this section.