 The first generation of Zenbooks was announced on October 11 , 2011 , one day before release , although they were first demonstrated at Computex 2011 in May that year . Two models were released in 2011 to positive reviews : the 11 inch UX21E and the 13 inch UX31E , also frequently known as the UX21 and UX31 respectively . The design of the UX21 drew comparisons to the Macbook Air and it was regarded as an " excellent rival " by CNET reviewer Andrew Hoyle . Other aspects of the laptops that reviewers liked were the Bang and Olufsen speakers , fast boot times due to Asus ' BIOS design and the speed of general tasks within the operating system resulting from the SSD and Sandy Bridge processors . However , the screens drew criticism for their poor contrast ratio , colour accuracy and less than perfect viewing angle , although they were praised for their brightness and the sharpness of the UX31 's screen . Reviewers also noted the shallow key @-@ press of the metal keyboard and lack of backlighting , a feature that Asus did not have time to implement before shipping . 
