Greek alphabet glottal ("heth") was borrowed in two different functions by different dialects of Greek: as a letter for /h/ (Η, heta) by those dialects that had such a sound, and as an additional vowel letter for the long (Η, eta) by those dialects that lacked the consonant. Eventually, a seventh vowel letter for the long (Ω, omega) was introduced. Greek also introduced three new consonant letters for its aspirated plosive sounds and consonant clusters: Φ ("phi") for , Χ ("chi") for and Ψ ("psi") for . In western Greek variants, Χ was instead used for and Ψ for . The origin
Greek alphabet transcription systems, and to what degree they attempt either an exact letter-by-letter transliteration or rather a phonetically-based transcription. Standardized formal transcription systems have been defined by the International Organization for Standardization (as ISO 843), by the United Nations Group of Experts on Geographical Names, by the Library of Congress, and others. During the Mycenaean period, from around the sixteenth century to the twelfth century BC, Linear B was used to write the earliest attested form of the Greek language, known as Mycenaean Greek. This writing system, unrelated to the Greek alphabet, last appeared in the thirteenth century BC. In the