Computer Technology is the study of the theoretical foundations of information and computation and their implementation and application in computer systems. Computer technology has many sub-fields; some emphasize the computation of specific results such as computer graphics, while others relate to properties of computational problems such as computational complexity theory. Still others focus on the challenges in implementing computation. For example, programming language theory studies to describe computation, while computer programming applies programming languages to solve specific problems. A further sub-field, human computer interaction, focuses on the challenges in making computers and computations useful, usable and universally accessible to people.