A good start when programming efficiently is to have knowledge about how much memory different data types and operations require. It is implementation-dependent how much memory the Erlang data types and other items consume, but here are some figures for erts-5.2 system (OTP release R9B). (There have been no significant changes in R12B.)
The unit of measurement is memory words. There exists both a 32-bit and a 64-bit implementation, and a word is therefore, 4 bytes or 8 bytes, respectively.
Data type | Memory size |
Integer (-16#7FFFFFF < i <16#7FFFFFF) | 1 word |
Integer (big numbers) | 3..N words |
Atom | 1 word. Note: an atom refers into an atom table which also consumes memory. The atom text is stored once for each unique atom in this table. The atom table is not garbage-collected. |
Float |
On 32-bit architectures: 4 words On 64-bit architectures: 3 words |
Binary | 3..6 + data (can be shared) |
List | 1 word per element + the size of each element |
String (is the same as a list of integers) | 2 words per character |
Tuple | 2 words + the size of each element |
Pid | 1 word for a process identifier from the current local node, and 5 words for a process identifier from another node. Note: a process identifier refers into a process table and a node table which also consumes memory. |
Port | 1 word for a port identifier from the current local node, and 5 words for a port identifier from another node. Note: a port identifier refers into a port table and a node table which also consumes memory. |
Reference |
On 32-bit architectures: 5 words for a reference from the current local node, and 7 words for a reference from another node. On 64-bit architectures: 4 words for a reference from the current local node, and 6 words for a reference from another node. Note: a reference refers into a node table which also consumes memory. |
Fun | 9..13 words + size of environment. Note: a fun refers into a fun table which also consumes memory. |
Ets table | Initially 768 words + the size of each element (6 words + size of Erlang data). The table will grow when necessary. |
Erlang process | 327 words when spawned including a heap of 233 words. |
The Erlang language specification puts no limits on number of processes, length of atoms etc., but for performance and memory saving reasons, there will always be limits in a practical implementation of the Erlang language and execution environment.