as . Transcription conventions for Modern Greek differ widely, depending on their purpose, on how close they stay to the conventional letter correspondences of Ancient Greek-based 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. History Origins 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 late ninth century BC or early eighth century BC, the Greek alphabet emerged. The period between the use of the two writing systems, during which no Greek texts are attested, is known as the Greek Dark Ages. The Greeks adopted the alphabet from the earlier Phoenician alphabet, one of the closely related scripts used for the West Semitic languages, calling it Φοινικήια γράμματα 'Phoenician letters'. However, the Phoenician alphabet is limited to consonants. When it was adopted for writing Greek, certain consonants were adapted to express vowels. The use of both vowels and consonants makes Greek the first alphabet in the narrow sense, as distinguished from the abjads used in Semitic languages, which have letters only for consonants. Greek initially took over all of the 22 letters of Phoenician. Five were reassigned to denote vowel sounds: the glide consonants (yodh) and (waw) were used for [i] (Ι, iota) and [u] (Υ, upsilon) respectively; the glottal stop consonant (aleph) was used for [a] (Α, alpha); the pharyngeal (ʿayin) was turned into [o] (Ο, omicron); and the letter for (he) was turned into [e] (Ε, epsilon). A doublet of waw was also borrowed as a consonant for [w] (Ϝ, digamma). In addition, the Phoenician letter for the emphatic 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