lunes, 29 de octubre de 2007

Transistores en un Microprocesador



El primer microprocesador fue el Intel 4004, producido en 1971. Se desarrolló originalmente para una calculadora, y resultaba revolucionario para su época. Contenía 2.300 transistores en un microprocesador de 4 bits que sólo podía realizar 60.000 operaciones por segundo. El primer microprocesador de 8 bits fue el Intel 8008, desarrollado en 1979 para su empleo en terminales informáticos. El Intel 8008 contenía 3.300 transistores. El primer microprocesador realmente diseñado para uso general, desarrollado en 1974, fue el Intel 8080 de 8 bits, que contenía 4.500 transistores y podía ejecutar 200.000 instrucciones por segundo. Los microprocesadores modernos tienen una capacidad y velocidad mucho mayores. Entre ellos figuran el Intel Pentium Pro, con 5,5 millones de transistores; el UltraSparc-II, de Sun Microsystems, que contiene 5,4 millones de transistores; el PowerPC 620, desarrollado conjuntamente por Apple, IBM y Motorola, con 7 millones de transistores, y el Alpha 21164A, de Digital Equipment Corporation, con 9,3 millones de transistores.

Eniac



ENIAC es un acrónimo inglés de Electronic Numerical Integrator And Computer (Computador e Integrador Numérico Electrónico), utilizada por el Laboratorio de Investigación Balística del Ejército de los Estados Unidos.

Máquina gigantesca que ha sido la primera computadora electrónica de propósito general (a excepción del Colossus, que fue usado para descifrar código alemán durante la Segunda Guerra Mundial y destruido tras su uso para evitar dejar pruebas, siendo recientemente restaurada para un museo británico) totalmente digital, es decir, que ejecutaba sus procesos y operaciones mediante instrucciones en lenguaje máquina, a diferencia de otras máquinas computadoras contemporáneas de procesos analógicos. Presentada en público el 15 de febrero de 1946.

La ENIAC fue construida en la Universidad de Pennsylvania por John Presper Eckert y John William Mauchly, ocupaba una superficie de 167 m² y operaba con un total de 17.468 válvulas electrónicas o tubos de vacío. Físicamente, la ENIAC tenía 17.468 tubos de vacío, 7.200 diodos de cristal, 1.500 relés, 70.000 resistencias, 10.000 condensadores y 5 millones de soldaduras. Pesaba 27 tn, medía 2,4 m x 0,9 m x 30 m; utilizaba 1.500 conmutadores electromagnéticos y relés; requería la operación manual de unos 6.000 interruptores, y su programa o software, cuando requería modificaciones, tardaba semanas de instalación manual.

La ENIAC elevaba la temperatura del local a 50ºC. Para efectuar las diferentes operaciones era preciso cambiar, conectar y reconectar los cables como se hacía, en esa época, en las centrales telefónicas, de allí el concepto. Este trabajo podía demorar varios días dependiendo del cálculo a realizar.

Uno de los mitos que rodea a este aparato es que la ciudad de Filadelfia, donde se encontraba instalada, sufría de apagones cuando la ENIAC entraba en funcionamiento, pues su consumo era de 160 kW. Esto no es cierto, ya que ésta tenía un sistema aparte de la red eléctrica.

A las 23.45 del 2 de octubre de 1955, la ENIAC fue desactivada para siempre.


Las mujeres del ENIAC

Aunque resulta frecuente encontrar en numerosos textos el nombre de los creadores del ENIAC - John Presper Eckert y John William Mauchly- no lo es tanto encontrar la referencia de quienes se encargaron de hacer funcionar la computadora. En la descripción del puesto de trabajo se decía: «Requiere esfuerzo, creatividad mental, espíritu innovativo y un alto grado de paciencia» ya que, por cierto, el ENIAC no tenía manual de programación.

Quienes se encargaron de que la computadora funcionara fueron seis mujeres: Kay Antonelli (1921-2006), Jean Bartik (1924- ), Betty Holberton (1917-2001), Marlyn Meltzer, Frances Spence (1922- ) y Ruth Teitelbaum (1924-86). Sus nombres fueron ocultados durante años y han sido recuperados recientemente para la historia de la computación.

Ellas que desarrollaron los primeros programas de software de la primera computadora electrónica y crearon el campo de la programación. A mediados de los cuarenta del siglo XX eran las únicas programadoras de computadoras de propósito general en el mundo. Fueron así las maestras de la primera generación de programadores digitales.

La historia de estas mujeres ha estado invisibilizada hasta que en 1986 una estudiante de Harvard, Kathryn Kleiman descubrió la historia de estas mujeres al realizar una investigación sobre el papel de las mujeres en la computación. La información fue difundida por Tom Petsinger que realizó un reportaje reconociendo el trabajo de las mujeres del ENIAC para Wall Street Journal.

Ellas, junto a la primera programadora en la historia del ordenador Ada Lovelace también conocida como Ada Byron, son claves en el desarrollo de la informática.


Descripción Técnica

La ENIAC pesaba 27 tn, medía 2,4 m x 0,9 m x 30 m y ocupaba una superficie de 167 m². Físicamente, la ENIAC tenía:

* 17.468 tubos de vacío
* 7.200 diodos de cristal
* 1.500 conmutadores electromagnéticos y relés
* 70.000 resistencias
* 10.000 condensadores
* 5 millones de soldaduras.


Prestaciones

La computadora podía calcular trayectorias de proyectiles, lo cual fue el objetivo primario al construirla. En 1.5 segundos era posible calcular la potencia 5000 de un número de hasta 5 cifras.

La ENIAC podía resolver 5.000 sumas y 360 multiplicaciones en 1 segundo. Pero entre las anécdotas estaba la poco promisoria cifra de un tiempo de rotura de 1 hora.

Goerge Boole




George Boole's parents were Mary Ann Joyce and John Boole. John made shoes but he was interested in science and in particular the application of mathematics to scientific instruments. Mary Ann was a lady's maid and she married John on 14 September 1806. They moved to Lincoln where John opened a cobbler's shop at 34 Silver Street. The family were not well off, partly because John's love of science and mathematics meant that he did not devote the energy to developing his business in the way he might have done. George, their first child, was born after Mary Ann and John had been married for nine years. They had almost given up hope of having children after this time so it was an occasion for great rejoicing. George was christened the day after he was born, an indication that he was a weak child that his parents feared might not live. He was named after John's father who had died in April 1815. Over the next five years Mary Ann and John had three further children, Mary Ann, William and Charles.

If George was a weak child after his birth, he certainly soon became strong and healthy. George first attended a school in Lincoln for children of tradesmen run by two Misses Clarke when he was less than two years old. After a year he went to a commercial school run by Mr Gibson, a friend of John Boole, where he remained until he was seven years old. His early instruction in mathematics, however, was from his father who also gave George a liking for constructing optical instruments. When he was seven George attended a primary school where he was taught by Mr Reeves. His interests turned to languages and his father arranged that he receive instruction in Latin from a local bookseller.

Having learnt Latin from a tutor, George went on to teach himself Greek. By the age of 14 he had become so skilled in Greek that it provoked an argument. He translated a poem by the Greek poet Meleager which his father was so proud of that he had it published. However the talent was such that a local schoolmaster disputed that any 14 year old could have written with such depth. By this time George was attending Bainbridge's Commercial Academy in Lincoln which he had entered on 10 September 1828. This school did not provide the type of education he would have wished but it was all his parents could afford. However he was able to teach himself French and German studying for himself academic subjects that a commercial school did not cover.

Boole did not study for an academic degree, but from the age of 16 he was an assistant school teacher at Heigham's School in Doncaster. This was rather forced on him since his father's business collapsed and he found himself having to support financially his parents, brothers and sister. He maintained his interest in languages, began to study mathematics seriously, and gave up ideas which he had to enter the Church. The first advanced mathematics book he read was Lacroix's Differential and integral calculus. He was later to realise that he had almost wasted five years in trying to teach himself the subject instead of having a skilled teacher. In 1833 he moved to a new teaching position in Liverpool but he only remained there for six months before moving to Hall's Academy in Waddington, four miles from Lincoln. In 1834 he opened his own school in Lincoln although he was only 19 years old.

In 1838 Robert Hall, who had run Hall's Academy in Waddington, died and Boole was invited to take over the school which he did. His parents, brothers and sister moved to Waddington and together they ran the school which had both boarding and day pupils. At this time Boole was studying the works of Laplace and Lagrange, making notes which would later be the basis for his first mathematics paper. However he did receive encouragement from Duncan Gregory who at this time was in Cambridge and the editor of the recently founded Cambridge Mathematical Journal. Boole was unable to take Duncan Gregory's advice and study courses at Cambridge as he required the income from his school to look after his parents. In the summer of 1840 he had opened a boarding school in Lincoln and again the whole family had moved with him. He began publishing regularly in the Cambridge Mathematical Journal and his interests were influenced by Duncan Gregory as he began to study algebra.

Boole had begun to correspond with De Morgan in 1842 and when in the following year he wrote a paper On a general method of analysis applying algebraic methods to the solution of differential equations he sent it to De Morgan for comments. It was published by Boole in the Transactions of the Royal Society in 1844 and for this work he received the Society's Royal Medal in November 1844. His mathematical work was beginning to bring him fame.

Boole was appointed to the chair of mathematics at Queens College, Cork in 1849. In fact he made an application for a chair in any of the new Queen's Colleges of Ireland in 1846 and in September of that year De Morgan, Kelland, Cayley, and Thomson were among those writing testimonials in support. De Morgan wrote (see for example [George Boole : his life and work (Dublin, 1985).',7)" onmouseover="window.status='Click to see reference';return true">7]):-

I can speak confidently to the fact of his being not only well-versed in the highest branches of mathematics, but possessed of original power for their extension which gives him a very respectable rank among their English cultivators of this day.

Kelland wrote:-

From the originality of his conceptions and the extent and accuracy of his knowledge, I conceive he has few superiors in Europe ...

Boole's father died in December 1848 before the decision had been made concerning the Irish chairs but an announcement came in August 1849 that Boole was to become the first Professor of Mathematics at Queen's College, Cork, and he took up the position in November. He taught there for the rest of his life, gaining a reputation as an outstanding and dedicated teacher. However the position was not without difficulty as the College became embroiled in religious disputes. Boole wrote to De Morgan on 17 October 1850 (see for example [George Boole : his life and work (Dublin, 1985).',7)" onmouseover="window.status='Click to see reference';return true">7]):-

... if you should hear of any situation in England that would be likely to suit me ... let me know of it. I am not terrified by the storm of religious bigotry which is at this moment raging round us here. I am not dissatisfied with my duties and I may venture to say that I am on good terms with my colleagues and with my pupils. But I cannot help entertaining a feeling ... that recent events in this College have laid the foundation of a lack of mutual trust and confidence among us ...

In May 1851 Boole was elected as Dean of Science, a role he carried out conscientiously. By this time he had already met Mary Everest (a niece of Sir George Everest, after whom the mountain is named) whose uncle was the professor of Greek at Cork and a friend of Boole. They met first in 1850 when Mary visited her uncle in Cork and again in July 1852 when Boole visited the Everest family in Wickwar, Gloucestershire, England. Boole began to give Mary informal mathematics lessons on the differential calculus. At this time he was 37 years old while Mary was only 20. In 1855 Mary's father died leaving her without means of support and Boole proposed marriage. They married on 11 September 1855 at a small ceremony in Wickwar. It proved a very happy marriage with five daughters: Mary Ellen born in 1856, Margaret born in 1858, Alicia (later Alicia Stott) born in 1860, Lucy Everest born in 1862, and Ethel Lilian born in 1864. MacHale writes [George Boole : his life and work (Dublin, 1985).',7)" onmouseover="window.status='Click to see reference';return true">7]:-

The large gap in their ages seemed to count for nothing because they were kindred spirits with an almost complete unity of purpose.

Let us now look at Boole's most important work. In 1854 he published An investigation into the Laws of Thought, on Which are founded the Mathematical Theories of Logic and Probabilities. Boole approached logic in a new way reducing it to a simple algebra, incorporating logic into mathematics. He pointed out the analogy between algebraic symbols and those that represent logical forms. It began the algebra of logic called Boolean algebra which now finds application in computer construction, switching circuits etc. Boole himself understood the importance of the work. He wrote in a letter to Thomson dated 2 January 1851 (see for example [George Boole : his life and work (Dublin, 1985).',7)" onmouseover="window.status='Click to see reference';return true">7]):-

I am now about to set seriously to work upon preparing for the press an account of my theory of Logic and Probabilities which in its present state I look upon as the most valuable if not the only valuable contribution that I have made or am likely to make to Science and the thing by which I would desire if at all to be remembered hereafter ...

Boole also worked on differential equations, the influential Treatise on Differential Equations appeared in 1859, the calculus of finite differences, Treatise on the Calculus of Finite Differences (1860), and general methods in probability. He published around 50 papers and was one of the first to investigate the basic properties of numbers, such as the distributive property, that underlie the subject of algebra.

Many honours were given to Boole as the genius in his work was recognised. He received honorary degrees from the universities of Dublin and Oxford and was elected a Fellow of the Royal Society (1857). However his career, which was started rather late, came to an unfortunately early end when he died at the age of 49. The circumstances are described by Macfarlane in [Lectures on Ten British Mathematicians of the Nineteenth Century (New York, 1916), 50-63. A pdf version',18)" onmouseover="window.status='Click to see reference';return true">18] as follows:-

One day in 1864 he walked from his residence to the College, a distance of two miles, in the drenching rain, and lectured in wet clothes. The result was a feverish cold which soon fell upon his lungs and terminated his career ....

What Macfarlane fails to say is that Boole's wife believed that a remedy should resemble the cause. She put Boole to bed and threw buckets of water over the bed since his illness had been caused by getting wet.

Hirst described Boole as:-

... evidently an earnest able and at the same time a genial man.

His work was praised by De Morgan who said:-

Boole's system of logic is but one of many proofs of genius and patience combined. ... That the symbolic processes of algebra, invented as tools of numerical calculation, should be competent to express every act of thought, and to furnish the grammar and dictionary of an all-containing system of logic, would not have been believed until it was proved. When Hobbes ... published his "Computation or Logique" he had a remote glimpse of some of the points which are placed in the light of day by Mr Boole.

Boolean algebra has wide applications in telephone switching and the design of modern computers. Boole's work has to be seen as a fundamental step in today's computer revolution.