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CREATION OF THE COMPUTER
&THE GRAND IDEAS OFCOMPUTER SCIENCE
The origin of computers, how they have developed and
the grand, foundational ideas.
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I. Pre-20th Century.
Before computers, there were...ALGORITHMS.Grand idea 1: Algorithms.An algorithm is a finite procedure for
computing a value. E.g. long division.May be done “in the head.”Note: Algorithms are abstract.
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Limitations…
This becomes difficult for large values, or large numbers of values. Need some kind of external aid, e.g. pebbles, or even a device, such as the abacus, a manual calculator.
Grand idea 2: Calculation devices.Problem—not automated.
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Mechanical Calculators.
Grand idea 3: problem-solving machines.1. The Pascaline, created by Blaise
Pascal, 17th Century, designed by Pascal to help his father calculate taxes. Could add & subtract semi-automatic could not multiply or divide.
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Mechanical Calculators.
2. The Stepped Reckoner, created by Gottfried Leibniz, 17th Century. Could multiply… how?
• Repeated addition. Could divide… how?
• Repeated subtraction.
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Limitations of Mechanical Calculators.
1. Moving parts -- so break down. Why? Parts wear down (friction, entropy).
2. Not programmable. Why? Cannot separate instructions (S/W) from the
physical machine (H/W).
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Mechanical Computer (partial).
Grand idea 4: General purpose computers.
The “Analytical Engine” of Babbage, England, 19th Century. Features:
1) Mill (gears, levers, belts, wheels), like? Processor
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Mechanical Computer (partial).
2) Store. Like? Memory
3) Punched Cards. Like? Programs.
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Punched Cards.
Grand idea 5: Programs.1. Origin?
The loom! (a programmable device -- different cards for different weaves).
2. How do cards work? Cards contain holes. Rods pass through holes and turn numbered
cogs.
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Punched Cards.
Therefore each card represents an instruction to turn certain cogs e.g. to add 1, 10 or a 100.1.
Idea: One card = 1 instruction.
A program = a series of instructions.
Therefore a program = a stack of cards.
This is the way computers were programmed up until the 1950’s.
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Why is the Analytical Engine important?
1. Not because it worked -- it didn’t.2. Because Babbage had the concept of a
true, general purpose computer: a device whose program could be changed a device which was not restricted to the
operations built into it.
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“Electric Tabulator” of Herman Hollerith, 19th Century, USA.
Grand idea 6: automatic computers.1. Used punched cards, but had electric
power.2. Used for U. S. Census.3. Led to the Tabulating Machine
Company, which eventually became… IBM
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George Boole. Mathematical breakthrough: binary notation.
Grand idea 7: Digital computers.Why is binary notation important to the
development of computers?1. All numbers can be represented by 0’s
and 1’s2. All instructions and data can be
represented by numbers. Therefore…..
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George Boole. Mathematical breakthrough: binary notation.
3. All instructions and data can be represented by 0’s and 1’s.
So what?O’s and 1’s can be physically represented
by a switch being on/off.
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How does this help?
Grand idea 8: Electronic digital computers.
Allows the development of electronic computers.
Electronic computers are series of switches, which can be either on or off, 0 or 1.
So, switches can be used to represent data and instructions in binary form.
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II. Twentieth Century.
4 Generations of electronic, digital computers. Each generation is defined in terms of the
hardware used for switches / circuits.1st Generation.
Used vacuum tubes as switches e.g. ENIAC. But…. Unreliable. Why? Could only be reprogrammed by physically re-
wiring.
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Von Neumann’s Stored Program Concept.
Von Neumann advanced the stored program concept, the idea that the program could be stored independently of the H/W and then loaded into memory when needed e.g. UNIVAC (still used vacuum tubes), but easier to program.
2nd Generation. Used Transistors. Magnetic memory.
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Silicon Fish and Chips.
3rd generation. Integrated circuit, transistors etched onto
silicon wafer by laser.
4th generation. LSI chips VLSI chips the microprocessor: computer on a chip.
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Advancements.
In each advance from one generation to the next, we notice that the computers improve in what ways? Faster Smaller Cheaper More reliable.
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Advances in PCs.
1970’s. Apple PC. Tandy. Games.1980. IBM - PC. (64k-256k!) Business.1987 386.1989 486.1993 PENTIUM I. 133MHZ.1995 P6.1998 PENTIUM III -- > 450MHZ2001 PENTIUM IV --> 2 GHZ+.