What is a computer? Computer is an electronic device that manipulate data. It has the ability to store, retrieve and process data.  Computer Structure Most computers in the modern world use the Von Neumann structure among other models such as the Harvard Model. The Von Neumann structure consists of 3 main parts, Input Output devices aka peripherals, CPU and Memory.  Von Neumann Architecture 1. Input / Output devices The Input devices include devices such as keyboards, mouses (or mice), sensors, and scanners. The Output devices include speakers, monitors and printers.  2. Memory unit The Memory unit sometimes called "Main Memory" stores the data and instructions from the input devices and the Central Processing Unit. It works closely with the CPU to execute calculations. There are 2 types of memories: RAM and ROM. 1. RAM (Main Memory) Random Access Memory, commonly abbreviated as RAM stores the data and instructions that the CPU requires. When the computer is powered off, all