CIO may take all the decisions regarding purchase and installation of hardware and software. Or he may take them in consultation with he CEO. It all depends on the size of organization and the sophistication of top management in regard to technological matters.
But increasingly CIO has to be educated about the business domain knowledge and has to take appropriate decisions by self.
Also the Role of the CIO is to buy management support for Tech. implementations, in addition to get the organisation ready for accepting the technology and the associated change management plan.