There are multiple support units in IT organization who helps delivery teams to reduce cost and better align with business. Units like Quality, System Operations, Security, Enterprise Architecture, Testing, Business Analyst, Data Engineering, Application Engineering and PMO office. How CIO/CTO office provides the common platform where all these team representative meets to evaluate the current state of IT and defines and leads to the future state?
Next question is to whom Head of Enterprise Architecture reports and how the CTO/CIO could extract optimum benefits from EA team. There are still unanswered questions like whether EA aligns better with Business or Delivery teams. A tilt towards business make EA more like Business Architects and other tilt towards the Delivery team moves EA's to Consultancy role. The focus of EA shifts from enterprise to projects. This wide spectrum is challenge, opportunity and concern for EA teams.
Again with my limited knowledge, I think most companies don't have EA function and who possesses this function are still trying to find a suitable place to fit the EA in organization chart.
Note: In above blog, I have typically avoided the differences between CIO and CTO. For more details on differences, please refer following links - Whatever happened to CTO role? and CIO vs CTO. Secondly, I have excluded product organizations from discussion and talking about IT organizations.