By Susan Wooldridge
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Additional resources for Data Processing. Made Simple
Mauchley and J. P. Historical Perspective 25 Eckert were working on an electronic computer at the Moore School of Electrical Engineering at the University of Pennsylvania. Their first result was the ENIAC (Electrical Numerical Integrator and Computer), which weighed over 30 tons and had more than 19,000 vacuum tubes— and 20 words of internal memory. It was designed to take over calcula tions on ballistic missiles then being done on the differential analyser. Eckert has described the advances in programming made, starting with the differential analyser: 'To change a problem on that machine, one had to take a set screw driver, release the set screws on perhaps a thousand gears, remove these gears from the machine, figure out where a new set of gears should go, hammer on the new set of gears, try running the machine, find fhat some of the set screws were loose, tighten them up and make various adjustments, and, after about four days' work suitable for an automechanic, one would be ready to run the problem.
Some actual cores used in modern computers are too small to be seen with the unaided eye, and the wires they are strung on are corres pondingly fine. Semiconductor Memories Semiconductors are the most widely used form of memories in to day's computers. They have replaced the core memories of the third generation. 31 32 Data Processing Made Simple A semiconductor is made by chemically depositing various sub stances (for example, silicon nitride, polycrystalline silicon, and silicon dioxide) onto a substrate or plate.
Fig. 17. Contents of memory after program execution. store the result in position 66. This is a three-address instruction. The final instruction is a stop, with no operand. The whole program is: 11 0007 27 0066 0098 21 0098 0099 0066 99 Fig. 16 shows the contents of memory before the program is exe cuted. Fig. 17 shows the contents of memory after the program has been executed. The instructions are accessed and executed one at a time by the control unit. The control unit feeds data to the arithmetic unit for any arithmetic that must be done, and gets the answer back to place in memory.