Basic Building Blocks of a Computer

Desktop Computer

Irrespective of whether it is the micro, mini, or mainframe, a computer is built using some basic building blocks. The concept of storing the instructions and data received from the outside world, into the memory of the computer and then retrieving them one by one and executing in sequential order (unless explicitly modified) is called the "Stored Program Concept". The idea is understood to have been given by John von Neumann and so the associated architecture is called von Neumann architecture

The concept, it appears, had been adopted from the human way of processing information (whatever has been understood or guessed about the way the human brain works). For example, if a person is told to do some calculation, first of all, the instructions and related data are taken into the storage area of the person's brain. The information enters the storage through ears (listening), eyes (seeing), hands (touching), etc. The brain's storage area may be termed as memory. The human body parts that help in entering the information inside the memory may be called input units. 

When the execution takes place we can imagine that the instructions are fetched from the memory, they are decoded and executed by some other functional block of the brain. The general function of this block would be to calculate by applying arithmetic and/or logic. So we can imagine that this function is carried out by an Arithmetic and Logic Unit of the brain. The result of calculations may either be sent back to memory for storing or may be declared to the outside world as the output of the processing. The body parts that do the transfer of information to the outside world may be called "output units". Our mouth (when we speak), our hands (when we write), even our eyes act as output units.

Besides these blocks, there is a need for another block that should control the operations of each of the blocks we have mentioned.

Sometimes one can notice not reading anything with an open book in front of the eyes. Possibly, because of some thoughts, the control unit of the brain does not allow the input block (eyes) to receive input data and also does not allow memory to receive data from the input block at those moments. This unit may be called the control unit of the brain. 

Computers are also built using similar five functional units or blocks. The following diagram shows the building blocks of a general-purpose computer. The arrow lines (thin) show the data flow. The thick arrow lines represent the control.

Traditionally the control unit and the ALU are built together and together they are termed as Central Processing Unit or CPU.

This basic architecture is at the root of all computers built today. There have been some variations but no major departure.

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