ADVANCEMENT OF CPU

The CPU first generated on a computer was all about using VACUUM TUBES that was the initial phase of designing a processor that could process the needs of the programmer.
Then came the second generation computers that used the TRANSISTORS.Unlike the vacuum tubes, which requires wires, metal plates, a glass capsule, and a vacuum, the transistor is a solid-state device, made from silicon.
Beyond the third generations there is less general agreement on defining generations of computers.
With the introduction of the VERY LARGE SCALE INTEGRATION (VLSI) more than 1000 components can be placed on a single integrated circuit chip.VLSI achieved more that 10,000 components per chip, while current ultra-large-scale integration (ULSI) chip can contain more than one million components.
The main advancement of using the VLSI design was the introduction to the MICROPROCESSORS and the MICROCONTROLLERS.

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

Functionality of a computer

A computer is a complex system,contemporary computers contain millions of elementary electronic components.Then how can we clearly describe how these work and function,hence we find the hierarchy of the system on order to resolve the functionality of each and every unit of the system,the same works with the computer too.
Hence we figure out a hierarchical format for the computer.
A hierarchical system if a set of interrelated subsystems, each of the latter, in turn, hierarchical in structure until we reach some lowest level of elementary subsystem.
The hierarchical nature of complex systems is essential to both their design and their description.The designer need only deal with a particular level of the system at a time.At each level,the system consists of a set of components and their interrelationships.The behavior at each level depends only on a simplified, abstract characterization of the system at the next lower level.
At each level, the designer is concerned with structure and function:
Structure:The way in which the components are interrelated.
Function: The operation of each individual components as part of the structure.

Basically to design a computer, we begin with the major components of a computer, describing their structure and functionality, and proceed to successively lower layers of the hierarchy.

Function:
Both the structure and the functionality of a computer are in essence and can be depicted by the following features that they perform that is the functionality of a computer or the functions that the computer can perform.They are:

• Data processing
• Data storage
• Data movement
• Control

The TOP-LEVEL structure of a computer:

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