During a keynote address at Pubcon in Las Vegas last week, Google’s Gary Illyes explained that the company is planning to create a separate mobile index soon that will serve as the primary index the engine uses for responding to search queries. There will also be a separate, less up-to-date desktop index maintained. The plan was first announced at last year’s SMX East. “It’s unclear exactly how the mobile index will work,” reports Search Engine Land. “For example, since the mobile index is the ‘primary’ index, will it really not be used for any desktop queries? Will it only contain ‘mobile-friendly’ content? How out-of-date will the desktop index be?”