CREATION OF THE COMPUTER & THE GRAND IDEAS OF COMPUTER SCIENCE The origin of computers, how they have developed and the grand, foundational ideas.

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.

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.

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.

Mechanical Calculators. 2. The Stepped Reckoner, created by Gottfried Leibniz, 17th Century. Could multiply… how? Repeated addition. Could divide… how? Repeated subtraction.

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).

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

Mechanical Computer (partial). 2) Store. Like? Memory 3) Punched Cards. Like? Programs.

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.

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.

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.

“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

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’s 2. All instructions and data can be represented by numbers. Therefore…..

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.

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.

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.

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.

Silicon Fish and Chips. 3rd generation. 4th generation. Integrated circuit, transistors etched onto silicon wafer by laser. 4th generation. LSI chips VLSI chips the microprocessor: computer on a chip.

Advancements. In each advance from one generation to the next, we notice that the computers improve in what ways? Faster Smaller Cheaper More reliable.

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 -- > 450MHZ 2001 PENTIUM IV --> 2 GHZ+.