CTO and CIO are often used as interchangeable titles. In one company the roles can genuinely be combined. In another they represent very different jobs.
So I would not define them by their expanded titles. It is more useful to look at the outcome each person owns.
A CIO Usually Looks Inward
Simplifying a little, a CIO is responsible for how technology helps the organization itself operate.
Corporate systems, data, internal process automation, infrastructure, security, and employee tools naturally fall into that area.
The main question is how well technology supports the business as an operating system.
A CTO Usually Looks at Technology as Part of Product and Strategy
A CTO tends to appear where technology is not only an internal service but part of what the company sells, scales, or uses as a competitive capability.
Product architecture, engineering organization, software quality, technology risk, and the ability to create new capabilities become part of business strategy.
The main question changes: which technology choices help the company move where it wants to go?
The Boundary Is Not Always Clean
In real companies, internal and product technology constantly overlap. Customer data feeds analytics. Platforms affect both product and operations. Security matters to both internal infrastructure and external services.
That is why trying to draw a perfect CTO/CIO boundary often produces a beautiful diagram that does not survive contact with reality.
The Problem Starts When There Are Two Titles but No Two Areas of Ownership
If the CTO and CIO both “own technology,” conflict is almost guaranteed. Who sets architecture standards? Who owns data? Who decides on platforms? Who owns security?
The title does not answer those questions.
It is much more useful to divide decisions, budgets, and outcomes explicitly.
Does a Company Need Both?
Not necessarily. In a smaller organization, one strong technology leader may cover both sides. As complexity grows, the areas may require different attention.
But splitting the roles simply because the company became large is not a strategy either. First there should be a management problem that the split actually solves.
How to Decide Which Profile You Need
If the main question is “how do we make internal systems, processes, and data more reliable and effective?”, you are probably closer to a CIO profile.
If the question is “how should technology evolve with the product and the business?”, you are probably closer to a CTO profile.
If both are painful, perhaps the company first needs one leader to build the technology function as a whole, with a role split later.
Do not search for the correct title. Search for the person who fits the technology responsibility you actually have.