GSM-7 alphabet
GSM-7 is the 7-bit alphabet used by default for SMS: it allows 160 characters per message but does not contain every accented character.
Definition
GSM-7 is the 7-bit alphabet used by default for SMS: it allows 160 characters per message but does not contain every accented character.
In detail
The GSM-7 alphabet encodes each character on 7 bits. Since an SMS payload is 140 bytes, that gives exactly 160 characters: the origin of the historic SMS limit.
The alphabet covers basic Latin letters, digits, common punctuation and a few accented characters, but not all of them. A message containing a character missing from the table switches to UCS-2, which sharply reduces capacity — hence the common practice of folding accents before sending.
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