Now computers have a long history but modern electronic computers got their start with the vacuum tube based machines of late forties and fifties. The vacuum tube, invented at the same time as the light bulb by none other than Thomas Edison, is what made electronic computers achievable. The great thing about these tubes was they were able to make signals stronger or amplify them. The tubes could also start and stop the flow of electricity. The first major of general purpose computer to use vacuum tubes was the ENIAC conceived and designed by John Mauchly and J. Presper Eckert of the University of Pennsylvania which consisted of eighteen thousand tubes[B1], seven thousand two hundred crystal diods, seventy thousand resistors ten thousand capasitors and five million hand soldered points. [pic]Pic.1
The trouble with the ENIAC was that it took up lots of room, 1800 square feet to be exact. Another problem with the machine was power consumption. It was said that the ENIAC would cause rolling brown outs but this was not true. It did however use 150 Kw of power. The heat generated by the machine was an addition difficulty to overcome. This was somewhat counteracted by large fans as seen in pic. 1 but the heat was so great that tubes still burnt out. Furthermore programming on the ENIAC was done using a large collection of plug boards and switches. It took several weeks to map out the program then several days to input the program into the computer. All this was followed by a period of debugging with the ability of going step by step to clean up problems and mistakes before beginning the computation.
The problems the vacuum tube machines had limited there use. To have a computer you needed the space but most of all the cost was what needed to be met. The cost was not only for what it took to develop and build the machine but also to keep it maintained with things like new parts especially the tubes. There also was large sections dedicated just for memory or program storage. These problems were lessened any way in 1947 with the invention of the point-contact transistor by John Bardeen and Walter Houser at AT&T's Bell Laboratories. This transistor consists of a block of germanium, a semiconductor, with two very closely spaced gold contacts held in agaist it by a spring as in pic. 2. To create the two contact points a small stip of gold foil is attached over the point of a plastic triangle. The gold is then carefully sliced through at the tip of the triangle. [pic]
Now the piece of germanium has a surface layer with an excess of electrons. When an electric signal is passed through the gold foil, it creates holes or points which lack electrons. If a small positive current is applied to one of the two contact points known as the emitter it causes a change or amplification in the second point or Collectors current. These transistors were used in some devices but was soon superseded by the bipolar junction transistor.
The bipolar junction transistor was invented by William Shockley at Bell Laboratories in 1947. this type of transistor relies on the contact of two types of semiconduter tooperate. The contact creates the regions in the transistor called emitter, collector, and base. A BJT consists of three differently doped semiconductor regions as mentioned. Each region is connected to a terminal appropriately labeled emitter (E), base (B), collector (C). The base made up of...