IRISH MUSIC FROM THE 6TH TO THE 9TH CENTURY

By the end of the 9th Century, the ancient Irish were responsible for the spread of music in Europe.

• They were acquainted with the ogham music tablature in pre-Christian ages; 
• They had their battle-marches, dance tunes, folk songs, chants. and hymns in the fifth century
• They were the earliest to adopt the neums or neumatic notation, for the plain chant of the Western Church; 
• They modified, and introduced Irish melodies into, the Gregorian Chant; 
• They had an intimate acquaintance with the diatonic scale long before it was perfected by Guido of Arezzo; 
• They were the first to employ harmony and counterpoint; 
• They had quite an army of bards and poets; 
• They employed blank verse, elegaic rhymes, consonant, assonant, inverse, burthen, dissyllabic, trisyllabic, and quadrisyllabic rhymes, not to say anything of caoines, laments, elegies, metrical romances, etc.; 
• They invented the musical arrangement which developed into the sonata form; 
• They had a world-famed school of harpers; 
• They generously diffused musical knowledge all over Europe.

Ancient Irish Music: Prior to 1100, there were no unified forms of musical tablature

The main reason there is no written record of Irish music prior to 1100 has to do with the systems in which the music was taught and performed:

The pre-Christian Irish had their ogham music-tablature, and the Irish of the seventh-eleventh century had the neumal accents, after which the Guidonian system was adopted The Guidonian hand was known in Ireland at the close of the eleventh century

Ogham = An ancient British and Irish alphabet, consisting of twenty characters formed by parallel strokes on either side of or across a continuous line.  The very word ogham suggests at once a musical signification, and, therefore, it is of the very highest importance to claim for Ireland the earliest form of musical tablature.
http://www.claddaghdesign.com/blog/history/a-guide-to-the-ogham-alphabet/

A neume (/ˈnjuːm/; spelled neum in, for instance, the Solesmes publications in English)[1][2][3] is the basic element of Western and Eastern systems of musical notation prior to the invention of five-line staff notation. The word is a Middle English corruption of the Greek word for breath (πνεῦμα pneuma).
http://en.wikipedia.org/wiki/Neume

The Guidonian hand was known in Ireland at the close of the eleventh century
http://en.wikipedia.org/wiki/Guidonian_hand