A typical computer is organized into four essential components: a central processing unit (CPU) to manipulate numbers; a primary memory that feeds data and instructions of immediate importance into the CPU; secondary or peripheral memory that stores data and programs until they are fed into the main memory; and input-output devices, which link the CPU and the information the computer will work with. _{Primary Memory.} Early computers stored instructions and data in bulky mechanical devices, vacuum tubes, or transistorized elements. These devices were most often fed by punched cards or paper tapes. In the 1950s several memory systems were developed. The most important of these was the magnetic core memory devised by Jay Forrester, an engineer at the Massachusetts Institute of Technology. His system used tiny magnetic "doughnuts" suspended on a gridwork of wires inside the computer. These discs could be electrically "flipped" with an electric...