The Secret History Of Evolution Of (a Brief History) Computer - Computer Architecture

Evolution of Computers-Brief History

History of computers Gives us the basic information about the technological development trends in computer in the past and its projections in the future.

The Secret History Of Evolution Of (a Brief History) Computer - Computer Architecture

The ancestors of modern age computers were the mechanical
and electromechanical devices. This ancestry can be traced as back as 17th century. when the first machine capable of performing four
mathematical operations, viz., addition, subtraction, division and

Mechanical Computers

Blaise Pascal made the very first attempt towards the automatic computing. He invented a device, which consisted of lots of gears and chains and used to perform repeated additions and subtractions.
This device was called Pascaline. Later many attempts were
made in this direction; we will discuss some details about the
innovation by Charles Babbage, the grandfather of modern
He designed two computers.

* The difference engine

It was based on the mathematical principle of finite differences and was used to solve calculations on large number using a formula. It was also used for solving the polynomial and
trigonometric functions.

* The analytical engine by Babbage

It was a general purpose computing device, which could be used for perferming any mathematic operation automatically. It consisted of the following components:
The store : A mechanical memory unit consisting of sets of counter wheels.
The mill : An arithmetic unit, which is capable of performing the four basic arithmetic operations.


There are basically two types of cards:

Types of Cards-
1.Operation Cards
2. Variable Cards

(i) Operation cards
Selects one of the four arithmetic operations by activating the
mill to perform the selected operation.

(ii) Variable cards
Selects the memory location to be used by the, mill for a particular operation (i.c. the source of the operands and the destination of the results).
Output : Could be directed to a printer or a card punch device.

The basic feature of this analytical engine were:
-It was a general purpose programmable machine.
-It had the provision of automatic sequence control, thus enabling programs to alter its sequence of operations.
-The provision of sign checking of result existed.
-Mechanism for advancing or reversing of control card was
permitted thus enabling execution of any desired instruction.
-In other words, Babbage has devised a conditional and
branching instructions.
-The Babbage machine is fundamentally the same as a
moden computer.

The First Generation : Vacuum Tubes
The first electronic computer was constructed using vacuum tubes. The first computer constructed using vacuum tube technology vas ENIAC (Electronic Numerical Integrator and Calculator).
-It was enormous machine weighing about 30 tons.
-It contained more than 18,000 vacuum tubes.
-It consumed 140 kilowatts of power.
-It was a decimal rather than a binary machine.
-It was capable of 5000 additions per second.
-It had memory to hold twenty 10 digit decimal numbers.
-It stored programs and data in separate memories.

EDVAC (Electronic Device Variable Computer)
ENIAC stored program and data in separate memories entering or altering program was a difficult task, EDVAC stores both program and data in the same memory.

Concept of common memory for both program and data
-EDVAC has two kinds of memory : a fast main memory with
a capacity of 1024 and slower secondary memory of 20k words.
-It stored and processed number in binary form to minimize
hardware cost. It processed data bit by bit.
-Prior to execution, a set of instructions forming a program is
placed in the EDVAC main memory. The instructions were then transferred one a time from the main memory to the CPU for execution.
-Each instruction had a well defined structure of the form:
-The meaning :perform the operation op (addition, subtraction, multiplication, etc.) on the contents of main memory locations A1, and A2, and then place the result In main memory location A3,A4 specifies the address of the next instruction to be executed.

The trends, which were encountered during the era of first-generation computers.

-Centralized control in a single CPU; all the operations required a direct intervention of the CPU.
-Use of ferrite-core main memory had started.
-Concept of virtual memory had started.
-Punched cards were used as input.
-Magnetic tapes and magnetic drums were used as secondary
-Binary code or machine language was used for programming.
-Towards the end due to diffīculties encountered in use of machine language as programming language, the use of symbolic language that is now called assembly language started.
-Assembler, a program that translates assembly language programs to machine language was made.
-Computer was accessible to only one programmer (single user mode).
-Advent of Von Neumann architecture.

The Second Generation: Transistors

-The use of the transistors defines the second generation of
-Vacuum tubes were replaced by transistors. The transistor is smaller, cheaper and dissipates less heat than a vacuum tube.
-The second-generation characterizes greater speed, larger memory capacity and a smaller size over the first generation.
-Computer hardware and software evolved rapidly after the introduction of the second-generation computers.
-Complex instructions were added to the set of instructions.
-More registers were added to the CPU to facilitate data and
address manipulation.
-Floating point number was introduced to support scientific 
-Input/output operations were added for easy transfer of the
information to and from peripheral devices like printer and
secondary memory
-High level programming languages were introduced.
-Provision of system software with the computer

The Third Generation :Integrated Circuits

This generation is associated with the introduction of Integrated Circuits (ICs) This replaced the discrete electronic circuits used in second generation camputers

ICs allowed a large number of transistors and associated
components to be combined on a tiny piece of silicon wafer.

IC technology initiated a long terms trend towards
(1) Higher speed
(2) Smaller size
(3) Lower hardware cost
(4) Lower power consumption
(5) More reliable circuit

IBM developed the most influential third generation computer, the system/360. The machine becamec a standard for all main frame computers.
-It was based on Von Neumann architecture.
-It had about 200 distinct instruction types
-It had many addressing modes.
-It supported various data types.
-It supported both fixed point and floating point numbers.
-It had 16 general purpose registers.
-The CPU had two major control states
(1) Supervisory state for use by the operating system.
(2) User state for executing application programs.

 Later Generations : VLSI 

VLSI allowed manufactures to fabricate a CPU, main
memory or even all the electronic circuit of a computer on a single
IC that can be mass produced at a very low cost. This resulted in a
new class of machines ranging from portable personal computers to
supercomputers that contain thousands of CPUS. Two most
important impact of VLSI are:
(1) Semiconductor memory
(2) Microprocessors

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