Introduction, Micro-Computer Architecture, Algorithm and Program as well as Applications :
NOTE : Before taking these electronic lessons about computers, we insist that it is imperative to have a very good knowledge of basic electronics and a very good knowledge of digital electronics. Required level : 2nd and 3rd cycle.
The computer is a machine that makes it possible to carry out automatically, thanks to pre-established programs, sets of logical and arithmetic operations, for scientific, accounting, scheduling, etc.
The programs and data to be processed are stored in a memory from which the work will be performed.
To carry out these tasks, the computer not only needs a hardware configuration, consisting of electrical and mechanical modules, but also a software context that includes the programs of the computer system exploitation.
We will come back to these different notions.
Figure 1 gives an image of the current computer in its working context.
To begin, we will make a little historical reminder and tribute to some scholars.
From the shield to the microcomputer.
The first calculating machine was probably the Chinese abacus appeared around 500 BC. In 1642, Blaise PASCAL developed his famous mechanical calculator, which was later improved. Then in the 17th century, JACQUARD invents a loom programmed with punch cards. In 1833, BABBAGE proposes its analytical machine, very complex for the time, inspired by the works of PASCAL and JACQUARD.
It is towards the end of the 19th century that HOLLERITH realizes the first electromechanical machine using punch cards. From this time and the beginning of the 20th century, it is industrial equipment with punch cards that appear. From 1936 to 1939, AIKEN and STIBITZ developed an automatic calculator using electromechanical relays.
The first electronic calculator, consisting of tubes is "ENIAC", operational from 1944. It is still a machine program cable. It is only in 1946 that NEWMANN elaborates the concept of recorded program which is a sequence of instructions stored in the memory of the calculator.
It is really at this time that appears the "computer" (ordinateur) whose essential difference compared to the "calculator" (calculatrice) is the flexibility of use due to the recorded program.
In 1950, the first commercial computer will be "UNIVAC I".
This first generation of computers is based on tube technology. Then at the end of the 1950, the second generation of transistor computers appeared.
A few years later (1964), it is the third generation that develops with the appearance of integrated circuits.
Finally, from the 70, the fourth generation of computers came into being with the creation of the first microprocessors. This new generation leads to microcomputers whose main constituent parts are made with integrated circuits L.S.I. (Figure 2).
Currently, there is a fairly successful electronic calculator market. There is also a type of intermediate machine between a calculator and a computer : it is the programmable calculator.
After this historical review, we will focus on the examination of the microcomputer and the microprocessor.
The microcomputer that appears in the early 70 has a microprocessor, complex integrated circuit, fulfilling the function of information processing.
A microcomputer is shown in Figure 3 in the form of a block diagram.
This microcomputer consists of the following sets :
-
The central processing unit
which processes and elaborates data. In this case, it is a microprocessor.
- The internal memories
constituted by the dead memories (ROM)
and by the vivid Memories (RAM).
These different memories store programs and data.
- The interfaces, or input-output circuits that connect the microcomputer with the outside world.
- The communication buses, consisting of a set of power lines, relate the sets described above. The buses are three in number : the data bus, bidirectional, allows the transit of information ; the unidirectional address bus transmits the addresses issued by the microprocessor ; finally, the control bus transmits the orders or commands necessary for the proper functioning of the assembly.
Through the interface circuits, peripheral assemblies are attached to the microcomputer.
Two of them are indispensable :
- The keyboard allows to introduce in the computer programs, data and commands.
- The screen (video monitor) allows you to view programs, data, results ...
In the case of a large computer, the keyboard-screen assembly constitutes a terminal. Several terminals can also be attached to a computer (in the case of multi-user computers).
Other devices, innumerable, can be connected to the microcomputer. Figure 4 shows all the devices that can be connected to the computer.
All the constituent parts of the microcomputer described above, as well as the peripherals connected to this microcomputer constitute the hardware. This English word means quincaillerie, it is actually the hardware part of the computer.
An algorithm is a logical sequence made of elementary prescriptions to be carried out in order, in order to solve a problem.
For example, for tea, you need :
take a pan
The fill with water
heat the water ...
It is often clearer to present the algorithm as a graph called a flow chart or flow chart. An example is given in Figure 5.
An algorithm (flowchart) is transcribed into a program that the microcomputer can understand. The program is therefore a sequence of instructions, expressed more or less elaborately according to the language used, which will be given to the microcomputer so that it executes them according to the logical path of the algorithm.
The programs (logiciels) constitute the software. Software is an English term meaning "soft material, paper". Indeed, a program is written on paper.
The program is stored in a memory that can be easily emptied and reloaded by another program. We obtain a great flexibility of use and the possibility of dealing with very different problems (scientists, management ...).
The two concepts of hardware and software are closely related and complementary to each other.
The hardware requires the implementation of a more and more advanced technology (microelectronics, complex integrated circuits, memories ...) which must be closely associated with software development.
We will return to the notion of algorithm by presenting an example.
EUCLIDE is the most famous Greek mathematician. Among all the arithmetic calculation methods that are assigned to it, there is one which is particularly interesting with which one determines the greatest common divisor (P.G.C.D.) of two natural whole numbers.
The method learned in college consists of breaking down each number into a series of prime factors and then multiplying the factors common to both numbers.
This method is an algorithm.
Example: Calculation of P G C D of 32 and 24
32 = 2 x 2 x 2 x 2 x 2
24 = 2 x 2 x 2 x 3
P G C D = 2 x 2 x 2 = 8
Suppose a microprocessor can compare two integers and make a difference when one is larger than the other.
This microprocessor can not calculate the P G C D with the factor decomposition method.
However, there is a second method stated by EUCLIDE which uses precisely the comparison of two numbers and the subtraction.
This method is as follows :
when the two numbers (A and B) are equal, the P G C D is equal to these two numbers,
if they are unequal, we make their difference that we compare to the smallest of them,
as long as there is no equality between the difference obtained and the smaller of the two numbers, this iterative process continues,
as soon as there is a tie, the P G C D is equal to the difference obtained (or to the smallest of the two numbers compared).
Let's go back to the previous example (32 and 24) :
32 and 24 are not equal, so we make the difference 32 - 24 = 8
8 and 24 are not equal, so we make the difference 24 - 8 = 16
16 and 8 are not equal, so we make the difference 16 - 8 = 8.
This time, the difference obtained (8) is equal to the smaller of the two numbers (8).
The P G C D is 8.
The flow chart for this problem is given in Figure 6.
Each rectangle and rhombus represents a step in the flow of the flowchart.
Each rectangle contains an instruction. These instructions are of three types.
The instructions of the first type refer to a fundamental operation which consists of assigning a data to a register while waiting to be processed. The contents of this register may vary during the execution of the organization chart. This fundamental operation is called attribution or assignment or allocation. In the example given, there are two variables (x and y) and four possible assignments (a, b, x - y and y - x).
The instructions of the second type are calculation instructions (x - y or y - x).
An instruction of the third type is that which stores the result in the register of the screen.
Both diamonds represent tests.
During a test, there is always a connection, that is to say that there are at least two directions from which a choice is made.
This flowchart defines the essential lines of the process for calculating P G C D.
This flowchart is transcribed in a programming language (Basic, Cobol, Assembler) in order to be executed by the microcomputer.
Today, the computer is present in most areas related to human activity as well as personal computers.
We will present a non-exhaustive inventory of the multiple applications of computers and computers.
2. 1. - SCIENTIFIC AND TECHNICAL APPLICATIONS
Historically, these are the first applications of the computer. Scientific research (physics, mathematics ...) requires simple operations (addition, subtraction ...) that are repeated a very large number of times.
The qualities of the computer (speed, capacity of the memory) made it possible to treat all these problems in an efficient and fast way.
These first applications were close to those of a calculating machine.
Currently, the use of computers has extended to all scientific disciplines (applied physics, medicine, statistics, natural sciences, weather forecasts). These disciplines often require the processing of large amounts of data. At the same time, this job has developed in the industrial sector.
This is the case of automation (programmable logic controllers, numerically controlled machine tools, robots, etc.) and industrial control processes (example : production line in a chemical plant).
Figure 7 shows a control room of an industrial process.
The computer is also present in the design offices (computer-aided design "C A O", industrial design).
Applications are developing at the level of the education system (computer assisted teaching "E A O").
Military applications, from the origins of computers, have been a stimulus for research and development (computing ballistics, guiding antiaircraft guns ...). More recently, these are space applications that have developed (automatic steering of rockets, satellites ...).
2. 2. - APPLICATIONS RELATED TO MANAGEMENT AND ADMINISTRATION
An important sector is that relating to the management of enterprises (PME and large public and private enterprises). The computer makes it possible to manage the stocks, to carry out the accounting, to follow the customers for example ... (to see the picture or the Figure 8 extracted from a catalog of our work, it is just a survey among so many other ...).
The utilities sector also uses the computer. This is the case of traffic and transport (traffic lights, tolls, booking for airplanes to have optimal filling, train tickets ...).
Posts and telecommunications also use computers (telephone exchanges, subscribers, databases ...).
A developing sector is that of the personal computer.
This sector affects the liberal professions (doctors, pharmacists ...) and the family structure (domestic management, video games ...).
This first theory ends with this overview on computer applications.
The following theory will allow you to deepen the theses addressed in this first part.
Introduction to the Computer
The two concepts of hardware and software are closely related and complementary to each other.
Click here for the next lesson or in the summary provided for this purpose.
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