In the early days of computer science, designers and developers paid much less attention to making hardware and software products usable or "user friendly." Yet, requests from a growing subset of users for easy-to-use devices eventually focused researchers' attention on usability.
The International Standards Organization (ISO) defines usability as "the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use." Thus, usability defines a set of criteria such as efficiency, safety, and utility, which are related mainly to computer systems.
In the mid-1990s, another important concept became associated with usability. User experience (UX) focuses mainly on parameters related to the user: satisfaction, enjoyability, emotional fulfillment, aesthetic appeal, and so on. The concept of UX has been extended and better defined in some research areas. For instance, web interface designers often leverage the User Experience Honeycomb to identify priorities in the design phase. The honeycomb's seven hexagons represent parameters that must be carefully balanced to provide users a satisfactory quality of experience (QoE) by ensuring that an interface is: useful, usable, desirable, findable, accessible, credible, and valuable.
Understanding humans' mental models is another important issue in HCI. Users learn and keep knowledge and skills in different ways, often influenced by their age as well as cultural and social backgrounds. Thus, HCI studies aim to bridge gaps between users and new technologies (which change nowadays quicker than in the past). Efficient, effective, and natural forms of HCI can reduce the skill levels needed to use complex devices, thus potentially reducing inequalities among people by helping to address an issue in the "digital divide" — the gap between those who have access to ICT technologies and skills to make use of those technologies and those who have neither the access nor the skills.
Source: Human-Computer Interaction: Present and Future Trends