Information Flow With in a Computer
The information that flows within a computer can be classified as
1. Programs and Data
2. Control Information
Programs and Data:
A program is what we have referred to earlier as description of the task to be performed by a computer. Data refers to a set of values assumed by the variables in Fthe program. For example, if we write a program to solve a quadratic equation ax2+bx+c=0, then the particular set of values of a b and c form the data for this programs. Thus, if one desires to solve a particular quadratic equation then he needs to feed in both programs and the data for that particular equation.
Programs and data enter the computer through an input device and get stored in the memory. The data which come in through on output devices is known as out put data or simply output from the computer.
Whenever any arithmetic operation is to be performed on the input data, it is to be transformed from memory to ALU. The arithmetic operation is performed to the users through on output device.
There is need to control the flow of instruction and appropriate data from memory to CPU. This requires various devices within a computer to behave in a controlled manner. This is accomplished by the control unit in CPU. The control unit controls various devices in the computer by sending them information in the form of controls signals. It can also ascertain the present status of the devices by getting status signals from the devices. For example, the control unit has to ascertain whether the output device is ready before signaling it to carry out the desired work (say printing etc). The controls unit controls these devices in accordance with the instruction in the user programs.