Computer lerning Point (Success Computer Education Point)

24/07/2015

A Brief Description
Preface

Computers are some of the most versatile tools that we have available. They are capable of performing stunning feats of computation, they allow information to be exchanged easily regardless of their physical location, they simplify many every-day tasks, and they allow us to automate many processes that would be tedious or boring to perform otherwise. However, computers are not "intelligent" as we are. They have to be told in no uncertain terms exactly what they're supposed to do, and their native languages are quite unlike anything we speak. Thus, there's a formidable language barrier between a person who wishes a computer to do something, and the computer that typically requires instructions in its native language, machine code, to do anything. So far, computers cannot figure out what they are supposed to do on their own, and thus they rely on programs which we create, which are sets of instructions that the computer can understand and follow.

An Overview of Programs and Programming Languages

In order to better communicate to our computers what exactly it is we want them to do, we've developed a wide range of programming languages to make the communication process easier.

Depending on the type of project, there are many factors that have to be considered when choosing a language. Here is a list of some of the more noteworthy ones:
Compiled, interpreted, or JIT-compiled
Compiled languages are translated to the target machine's native language by a program called a compiler. This can result in very fast code, especially if the compiler is effective at optimizing, however the resulting code may not port well across operating systems and the compilation process may take a while.
Interpreted languages are read by a program called an interpreter and are executed by that program. While they are as portable as their interpreter and have no long compile times, interpreted languages are usually much slower than an equivalent compiled program.
Finally, just-in-time compiled (or JIT-compiled) languages are languages that are quickly compiled when programs written in them need to be run (usually with very little optimization), offering a balance between performance and portability.

High or Low Level Level, in this case, refers to how much the nature of the language reflects the underlying system. In other words, a programming language's level refers to how similar the language is to a computer's native language. The higher the level, the less similar it is.
A low-level language is generally quite similar to machine code, and thus is more suitable for programs like device drivers or very high performance programs that really need access to the hardware. Generally, the term is reserved for machine code itself and assembly languages, though many languages offer low-level elements. Since a low-level language is subject to all the nuances of the hardware it's accessing, however, a program written in a low-level language is generally difficult to port to other platforms. Low level languages are practically never interpreted, as this generally defeats the purpose.
A high-level language focuses more on concepts that are easy to understand by the human mind, such as objects or mathematical functions. A high-level language usually is easier to understand than a low-level language, and it usually takes less time to develop a program in a high-level language than it does in a low-level language. As a trade-off one generally needs to sacrifice some degree of control over what the resulting program actually does. It is not, however, impossible to mix high-level and low-level functionality in a language.

Type System
A type system refers to the rules that the different types of variables of a language have to follow. Some languages (including most assembly languages) do not have types and thus this section does not apply to them. However, as most languages (including C++) have types, this information is important.
Type Strength: Strong or Weak
A strong typing system puts restrictions on how different types of variables can be converted to each other without any converting statements. An ideal strong typing system would forbid implicit "casts" to types that do not make any sense, such as an integer to a Fruit object. A weak typing system would try to find some way to make the cast work.

Type Expression: Manifest or Inferred
This deals with how the compiler/interpreter for a language infers the types of variables. Many languages require variables' types to be explicitly defined, and thus rely on manifest typing. Some however, will infer the type of the variable based on the contexts in which it is used, and thus use inferred typing.

Type Checking: Static or Dynamic
If a language is statically typed, then the compiler/interpreter does the type checking once before the program runs/is compiled. If the language is dynamically type checked, then the types are checked at run-time.

Type Safety: Safe or Unsafe
These refer to the degree to which a language will prohibit operations on typed variables that might lead to undefined behavior or errors. A safe language will do more to ensure that such operations or conversions do not occur, while an unsafe language will give more responsibility to the user in this regard.

These typing characteristics are not necessarily mutually exclusive, and some languages mix them.

Supported paradigms
A programming paradigm is a methodology or way of programming that a programming language supports. Here is a summary of a few common paradigms:
Declarative
A declarative language will focus more on specifying what a language is supposed to accomplish rather than by what means it is supposed to accomplish it. Such a paradigm might be used to avoid undesired side-effects resulting from having to write one's own code.

Functional
Functional programming is a subset of declarative programming that tries to express problems in terms of mathematical equations and functions. It goes out of its way to avoid the concepts of states and mutable variables which are common in imperative languages.

Generic
Generic programming focuses on writing skeleton algorithms in terms of types that will be specified when the algorithm is actually used, thus allowing some leniency to programmers who wish to avoid strict strong typing rules. It can be a very powerful paradigm if well-implemented.

Imperative
Imperative languages allow programmers to give the computer ordered lists of instructions without necessarily having to explicitly state the task. It can be thought of being the opposite of declarative programming.

Structured
Structured programming languages aim to provide some form of noteworthy structure to a language, such as intuitive control over the order in which statements are executed (if X then do Y otherwise do Z, do X while Y is Z). Such languages generally deprecate "jumps", such as those provided by the goto statement in C and C++.

Procedural
Although it is sometimes used as a synonym for imperative programming, a procedural programming language can also refer to an imperative structured programming language which supports the concept of procedures and subroutines (also known as functions in C or C++).

Object-Oriented
Object-Oriented programming (sometimes abbreviated to OOP) is a subset of structured programming which expresses programs in the terms of "objects", which are meant to model objects in the real world. Such a paradigm allows code to be reused in remarkable ways and is meant to be easy to understand.

Standardization
Does a language have a formal standard? This can be very important to ensure that programs written to work with one compiler/interpreter will work with another. Some languages are standardized by the American National Standards Institute (ANSI), some are standardized by the International Organization for Standardization (ISO), and some have an informal but de-facto standard not maintained by any standards organization.

22/09/2013

Central Processing Unit (CPU) or the processor is also often called the brain of computer. CPU (Figure 2.1) consists of Arithmetic Logic Unit (ALU) and Control Unit (CU). In addition, CPU also has a set of registers which are temporary storage areas for holding data, and instructions. ALU performs the arithmetic and logic operations on the data that is made available to it. CU is responsible for organizing the processing of data and instructions. CU controls and coordinates the activity of the other units of computer. CPU uses the registers to store the data, instructions during processing.

22/09/2013

Bioraphy and Education
Charles Babbage was born in London Dec. 26, 1791, St. Stephan day, in London. He was son of Benjamin Babbage, a banking partner of the Praeds who owned the Bitton Estate in Teignmouth and Betsy Plumleigh Babbage. It was about 1808 when the Babbage family decided to move into the old Rowdens house, located in East Teignmouth, and Benjamin Babbage became a warden of the nearby church of St. Michael.

The father of Charles was a rich man, so it was possible for Charles to receive instruction from several elite schools and teachers during the course of his elementary education. He was about eight when he had to move to a country school to recover from a dangerous fever. His parents sentenced that his "brain was not to be taxed too much"; Babbage wrote: "this great idleness may have led to some of my childish reasonings."
Then, he joined King Edward VI Grammar School in Totnes, South Devon, a thriving comprehensive school that's still operative today, but his fragile health status forced him back to private teaching for a period. Then, he finally joined a 30-student closed number academy managed by Reverend Stephen Freeman. The academy had a big library, where Babbage used to study mathematics by himself, and learned to love it. He had two more personal tutors after leaving the academy. One was a clergyman of Cambridge, and about him Babbage said: "I fear I did not derive from it all the advantages that I might have done.". The other one was an Oxford tutor who teached Babbage the Classics, so that he could be accepted to Cambridge.

Babbage arrived at Trinity College, Cambridge in October 1810. He had a big culture - he knew Lagrange, Leibniz, Lacroix, Simpson... and he was seriously disappointed about the math programs available at Cambridge. So he, with J.Herschel, G.Peacock, and other friends, decided to form the Analytical Society.

When, in 1812, Babbage transferred to Peterhouse, Cambridge, he was the best mathematician; but he failed to graduate with honours.
He received an honorary degree later, without even being examinated, in 1814.

In 1814, Charles Babbage married Georgiana Whitmore at St. Michael's Church in Teignmouth, Devon. His father, for some reason, never gave his approvation. They lived in tranquility at 5 Devonshire Street, Portland Place, London.
Only Three of their 8 children became adult.
Tragically, Charles' father, his wife and one of his sons all died in 1827.
Children

Benjamin Herschel Babbage (1815)
Charles Whitmore Babbage (1817)
Georgiana Whitmore Babbage (1818)
Edward Stewart Babbage (1819)
Francis Moore Babbage (1821)
Dugald Bromheald Babbage (1823)
Henry Prevost Babbage (1824)
Alexander Forbes Babbage (1827)
Timothy grant Babbage (1829)

Design of computers
In Babbage's times there was a really high error rate in the calculation of math tables, when Babbage planned to find a new method that could be use to make it mechanically, removing the human error factor. This idea started to tickle his brain very early, in 1812.
Three different elements influenced him in this decision: he disliked untidiness and unprecision; he was very able with logarithmical tables; he was inspired from an existing work on calculating machines produced by W. Schickard, B.Pascal, and G. Leibniz.
He discussed the main principles of a calculating engine in a letter he wrote to Sir H. Davy in the early 1822.
Difference engine
Babbage presented something that he called "difference engine" to the Royal Astronomical Society on Jun 14, 1822 and in a paper entitled "Note on the application of machinery to the computation of astronomical and mathematical tables."
It was able to calculate polynomials by using a numerical method called the differences method.
The Society approved the idea, and the government granted him £1500 to construct it, in 1823. Charles Babbage converted one of the rooms in his home to a workshop and hired Joseph Clement to oversee construction of the engine. Every part had to be formed by hand using custom machine tools, many of which Babbage himself designed. He took extensive tours of industry to better understand manufacturing processes. Based on these trips and his experience with the difference engine, Babbage published On the Economy of Machinery and Manufacture in 1832. It was the first publication on what we would now call operations research.

The death of Georgiana, Babbage's father, and an infant son interrupted construction in 1827. Work had already taxed Babbage heavily and he was on the edge of a breakdown. John Herschel and several other friends convinced Babbage to take a trip to Europe to recuperate. He passed through the Netherlands, Belgium, Germany, and Italy visiting universities and manufacturing facilities.

In Italy he learned he had been named the Lucasian Professor of Mathematics. He initially wanted to turn down the position but several friends convinced him to accept. He moved to 1 Dorset Street upon returning to England in 1828.

The difference engine project had come under fire during Babbage's absence. Rumours had spread that Babbage had wasted the government's money; that the machine did not work; and that it had no practical value if it did. John Herschel and the Royal Society publicly defended the engine. The government continued its support, advancing £1500 on April 29, 1829, £3000 on December 3, and £3000 on February 24, 1830. Work continued, but Babbage would have continual difficulty getting money from the treasury.

Babbage's problems with the treasury coincided with numerous disagreements with Clement. Babbage had built a two-story, 50 foot long workshop behind his house. It had a glass roof for lighting, and a fireproof, dust-free room to contain the machine. Clement refused to move his operations to the new workshop and demanded more money for the difficulty of travelling across town to oversee construction. In response, Babbage suggested that Clement draw his pay directly from the treasury. Before then, Babbage would get money from the government that he would use to pay Clement. He often had to pay Clement out of his own pocket when the bureaucracy lagged behind Clement's pay schedule. Clement refused the request and stopped working.

Clement further refused to turn over the drawings and tools used to build the difference engine. After an investment of £23000, including £6000 of Babbage's own money, work on the unfinished machine ceased in 1834. Charles wrote, "The drawings and parts of the Engine are at length in a place of safety—I am almost worn out with disgust and annoyance at the whole affair." In 1842 the government officially abandoned the project.
Analytical engine
While he was separated from the difference engine, Babbage began to think about an improved calculating engine. Between 1833 and 1842 he tried to build a machine that would be programmable to do any kind of calculation, not just ones relating to polynomial equations. The first breakthrough came when he redirected the machine's output to the input for further equations. He described this as the machine "eating its own tail". It did not take much longer for him to define the main points of his analytical engine.

The mature analytical engine used punched cards adapted from the Jacquard loom to specify input and the calculations to perform. The engine consisted of two parts: the mill and the store. The mill, analogous to a modern computer's CPU, executed the operations on values retrieved from the store, which we would consider memory. It was the world's first general-purpose computer.

A design for this emerged by 1835. The scale of the work was truly incredible. Babbage and a handful of assistants created 500 large design drawings, 1000 sheets of mechanical notation, and 7000 sheets of scribbles. The completed mill would measure 15 feet tall and 6 feet in diameter. The 100 digit store would stretch to 25 feet long. Babbage constructed only small test parts for his new engine; a full engine was never completed. In 1842, following repeated failures to obtain funding from the First Lord of the Treasury, Babbage approached Sir Robert Peel for funding. Peel refused, and offered Babbage a knighthood instead. Babbage refused. He would continue modifying and improving the design for many years to come.

In October 1842, Federico Luigi, Conte Menabrea, an Italian general and mathematician, published a paper on the analytical engine. Augusta Ada King, Countess of Lovelace, a longtime friend of Babbage, translated the paper into English. Charles suggested that she add notes to accompany the paper. In a series of letters between 1842 and 1843, the pair collaborated on seven notes, the combined length of which was three times longer than the actual paper. In one note Ada prepared a table of ex*****on for a program that Babbage wrote to calculate the Bernoulli numbers. In another, she wrote about a generalized algebra engine that could perform operations on symbols as well as numbers. Lovelace was perhaps the first to grasp the more general goals of Babbage’s machine, and some consider her the world's first computer programmer. She began work on a book describing the analytical engine in more detail, but it was never finished.
Second Difference Engine
Between October 1846 and March 1849 Babbage started designing a second difference engine using knowledge gained from the analytical engine. It used only about 8000 parts, three times fewer than the first. It was a marvel of mechanical engineering.

Unlike the analytical engine that he continually tweaked and modified, he did not try to improve the second difference engine after completing the initial design. Babbage made no attempt to actually construct the machine.

The 24 schematics remained in the Science Museum archives until a full-size replica was built 1985-1991 to celebrate the 200th anniversary of Babbage’s birth. It measured 11 feet long, 7 feet high and 18 inches deep, and weighted 2.6 tonnes. The limits of precision were restricted to those achievable by Babbage.
Babbage's accomplishments
In 1824 Babbage won the Gold Medal of the Royal Astronomical Society "for his invention of an engine for calculating mathematical and astronomical tables".

From 1828 to 1839 Babbage was Lucasian professor of mathematics at Cambridge. He contributed largely to several scientific periodicals, and was instrumental in founding the Astronomical Society in 1820 and the Statistical Society in 1834.

In 1837, responding to the official eight Bridgewater Treatises "On the Power, Wisdom and Goodness of God, as manifested in the Creation", he published his Ninth Bridgewater Treatise putting forward the thesis that God had the omnipotence and foresight to create as a divine legislator, making laws (or programs) which then produced species at the appropriate times, rather than continually interfering with ad hoc miracles each time a new species was required. The book incorporated extracts from correspondence he had been having with John Herschel on the subject.

Charles Babbage also achieved notable results in cryptography. He broke Vigenère's autokey cipher as well as the much weaker cipher that is called Vigenère cipher today. The autokey cipher was generally called "the undecipherable cipher", though owing to popular confusion, many thought that the weaker polyalphabetic cipher was the "undecipherable" one. Babbage's discovery was used to aid English military campaigns, and was not published until several years later; as a result credit for the development was instead given to Friedrich Kasiski, who made the same discovery some years after Babbage.

Babbage also invented the pilot (also called a cow-catcher), the metal frame attached to the front of locomotives that clears the tracks of obstacles in 1838. He also performed several studies on Isambard Kingdom Brunel's Great Western Railway.

He only once endeavoured to enter public life, when, in 1832, he stood unsuccessfully for the borough of Finsbury. He came in last in the polls.
Parts of Babbage's uncompleted mechanisms are available for visits in the London Science Museum. In 1991 a difference engine was completed, starting from Babbage's original plans, and it functioned perfectly.
References and Bibliography

- Passages from the Life of a Philosopher (Charles Babbage).
- Charles Babbage: Pioneer of the Computer (Anthony Hyman).
- Irascible Genius: A Life of Charles Babbage, Inventor (Maboth Moseley).
- The Cogwheel Brain (Doron Swade).
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