Computers constantly surround us in everything we do. From personal computers which we use to work and browse the internet, to unseen computers in lifts, cars and other systems.
When we talk about a computer, or digital computer, we are talking about an electronic calculating device that accepts digitized input, processes it by using a set of internal instructions and outputs the resulting information.
Not so cryptically, a digital computer accepts numerical information, which it calculates based on a set of internal instructions, to produce the desired information.
This set of internal instructions is called a program. The thing that makes computers so powerful is that these programs can be added and removed from the computer at will, making it a powerful multi-purpose machine. These removable programs are called software.
Computer architecture refers to those parts of a system that deal directly with the logical execution of a program. Computer organization refers to the operational units and their interconnections that allow for the logical execution of programs.
The archectural aspects focus more on the functionality of the system whereas the organization focuses more on the performance of the system.