MediaTek was the first to announce a chipset with a true octa-core processor back in June and now the first phone utilizing it has gone official. The UMI X2S broke cover at the Autumn Edition of Hong Kong Electronics Fair. All of UMI's phones are intended for the Chinese market and that's why you've probably never heard of the brand. The UMI latest X2S smartphone is powered by MT6592 chipset...
Source: http://www.gsmarena.com/umi_x2s_is_first_to_use_true_octacore_chipset_by_mediatek-news-7011.php
