The Arabic alphabet has twenty eight letters. More complex than differing capital and small letters in English, each Arabic letter may have up to four forms, depending on where it appears in the word and which letters precede or follow it. The Arabic script is read from right to left.
The cursive nature of the script and the vairability of the letterforms made it difficult to adapt Arabic for use with early printing presses. It is for this reason that the Arab world continued for some centuries after the time of Gutenberg to rely on handwriting for the production of books, especially the Qur'an. This was perhaps one of the reasons that calligraphy emerged as the most important Arab art form.
Source: Saudi Aramco World, (January-February 2002)