THE HEART OF THE COMPUTER

CENTRAL PROCESSING UNIT

The Central Processing Unit (CPU) or processor is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions.Hence it is being termed as the heart of the computer. This term has been in use in the computer industry at least since the early 1960s . The form, design and implementation of CPU's have changed dramatically since the earliest examples, but their fundamental operation remains much the same.

Early CPUs were custom-designed as a part of a larger, sometimes one-of-a-kind, computer. However, this costly method of designing custom CPUs for a particular application has largely given way to the development of mass-produced processors that are made for one or many purposes. This standardization trend generally began in the era of discrete transistor mainframes and minicomputers and has rapidly accelerated with the popularization of the integrated circuit (IC). The IC has allowed increasingly complex CPUs to be designed and manufactured to tolerances on the order of nanometers. Both the miniaturization and standardization of CPUs have increased the presence of these digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in everything from automobiles to cell phones and children toys

CPU is actually a silicon chip with complicated circuit embedded on it.The CPU has the following parts in it.They are:

1. CONTROL UNIT
2. ARITHMETIC AND PROCESSING UNIT

It also has number of registers it uses so as to reduce the memory usage.
They are:

1. Program counter(PC)
2. Instruction decoder
3. Instruction register(IR)
4. Process status register
5. Accumulator(AC)
6. Some general purpose registers

How is a computer designed?

Design of a computer:
The design of a computer depicts the nature and functionality of system that would be used by the programmer indeed to execute his versions.
hence to depict the nature of the system we have two basic aspects that are most important for the computers to be designed.They are
1.Computer architecture and
2.Computer organization.
Let us know how do these terms differ by each other
Computer architecture: refers to those attributes of a system visible to a programmer or in other way that have a direct impact to the logical execution of a program designed by a programmer.Examples of the architectural attributes include the instruction set, the number of bits used to represent various data types,input/output mechanisms and techniques for addressing memory.
Computer organization: refers to the operational units and their interconnections that realize the architectural specifications.Examples of the organizational attributes are
those hardware details transparent to the programmer,such as control signals,interfaces between the computer and peripherals,and the memory technology used.

In a class of computer called the microcomputers, the relationship between the architecture and the organization is very close.Changes in technology not only influence organization but also result in the introduction of more powerful and more complex architectures.
Generally,there is less of a requirement for generation-to-generation compatibility for these smaller machines.Thus,there is more interplay between organizational and architectural decisions