The first Perso-Arabic derived alphabet for Uyghur was developed in the 10th century, when Islam was introduced to the Uyghur people. The version used for writing the Chagatai language, which became the regional literary language, is now known as the Chagatay alphabet, and was used nearly exclusively up to the early 1920s. Alternative Uyghur scripts began being created then, and have collectively largely displaced Chagatai; Kona Yëziq, meaning "old script", now distinguishes it and UEY from the alternatives that are not derived from Arabic.
MS Windows Uyghur keyboard layout. Note that vowels are still using the older alphabet from the Arabic script, and not the newer plain letters of the Uyghur Ereb Yëziqi alphabet (composed of pairs of Arabic letters, starting by an alef with hamza, that must be entered separately on this keyboard before the actual vowel). In fact, the keyboard is also based on the older Latin alphabet used for the Mixed Uyghur Yëngi Yëziq, and does not allow entering all vowels correctly for the current Arabic script, but it more closely matches the older Chatagai script, which is now deprecated for Uyghur, for which it is considered suitable only for the Kona Yëziq, i.e. "old script".
A Pinyin-derived Latin-based alphabet (with additional letters borrowed from Cyrillic), then called “New script” or Uyghur Yëngi Yëziq or UYY, was for a time the only officially approved alphabet used for Uyghur in Xinjiang. It had technical shortcomings and met social resistance; Uyghur Ereb Yëziqi or UEY, an expansion of the old Chagatai alphabet based on the Arabic script, is now recognized, along with a newer Latin-based alphabet called Uyghur Latin Yëziqi or ULY, replacing the former Pinyin-derived alphabet; UEY is sometimes intended when the term "Kona Yëziq" is used.