A system’s IT infrastructure is the set of components, while its IT architecture is how they work together. Simply put, a system is built on top of an IT infrastructure that has a specific IT architecture.
There is no universal definition for ICT, but it is generally agreed that it has more to do with communications between people than IT does. While IT deals with computer systems, ICT is more inclusive of technology that allows you to communicate with others and is a direct extension of IT.
Information technology consists of the architecture, software, hardware, and networking of computers.