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Computing devices

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• Etymology of the word computer
  • Origin of the word Computer:

    Computer is derived directly from the Latin computus and computare. Both Latin words mean the same as the English verb compute: Compute = to determine by mathematical means. Computare = com + putare (Latin root words) Putare means to reckon Com is an intensifying prefix. (An intensifying prefix heightens or stresses, but does not change the meaning of the word it modifies Example: inflammable)

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• What is a computer
  • Computer:

    A computer is a "reckoning" or computing device.... In fact: a computer is an programmable computing device (that helps humans do their chores)

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  • How was the computer developed/invented:

    Humans had invented computing devices in ancient times. In the industrial revolution, programmable machines were invented

  • The computer is a combination of these 2 ideas.

    The Computer was invented by Alan Turing during World War II (to break the German Enigma code)

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• Some computing devices invented throughout history
  • "Ancient" computing device: the abacus

    Toy abacus	Real abacus
    # beads in row 1 = unit value # beads in row 2 = 10's value # beads in row 3 = 100's value And so on	# beads in column 1 = unit value # beads in column 2 = 10's value # beads in column 3 = 100's value And so on 1 bead in upper half = 5 beads in lower half Value represented by abacus = 63571

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  • 1822: Babbage's difference engine

    Babbage's difference engine	Close-up of the mechanics

  • Operation:

    The difference engine consists of a number of columns, numbered from 1 to N. The machine is able to store one decimal number in each column. The machine can only add the value of a column k + 1 to column k to produce the new value of k. Column N can only store a constant, Column 1 displays (and possibly prints) the value of the calculation on the current iteration.

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  • I have used one of these gadgets when I worked as cashier in my Dad's grocery store:

    Not the same model that I used, but it's similar. The device can only add and subtract.

    Initially, you press the clear button and pull the lever to reset the running sum to 0.

    To add a number to the running sum, you press the black and white buttons to form the number you want to add and pull the lever on the right: the input number is added to the running total. After the addition, the buttons will pop up by themselves (so you can enter a new value to add).

    BTW: there is no 0 digit - if you do not press any button in a column, the digit in that column is equal to 0.

    If you press the red button, the machine will perform subtraction

    You can sorta multiply too: one of the button in the right most column will lock the digits pressed. So after the addition, the same keys will remain "pressed". You can pull the level N times to multiply by N. (So it's only practical if you multiply by a small number, e.g., you will have to pull the level 12345 times if you multiply by 12345....)

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Programmable devices

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• Programmable machines, programs and instructions
  • Programmable machine:

    Programmable machine = a device which function can be altered by a program

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  • Program:

    Program = a series of instructions that accomplishes a specific task

    Example:

    Each row of holes in the card board is an instruction for some machine The position of a hole encodes a certain meaning The program consists of a series of rows (= instructions) on the card board

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• Examples of Programmable machines

  • Examples:

    Mechanical piano/music box	Mechanical loom
    A mechanical piano can play different songs The drum in the center of the piano contains spikes and rotates slowly Spikes at different position causes the piano to play a different note Different spike patterns (on different drums) will cause the piano to play a different song	The mechanical loom can weave fabric in different patterns The loom's movement is controlled by holes punched in a card Different hole patterns (on different cards) will casue the loom to weave a different pattern See: http://en.wikipedia.org/wiki/Joseph_Marie_Jacquard

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• Instruction encoding

  • Instructions (= program instructions) tells a machine what to do

  • Instructions are represented using a encoding method

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  • Example encoding:

    1 means add 2 means subtract And so on.

  • Another example: encoding a song on paper

    The location of a hole in the paper corresponds to a particular musical note Encoding a song: a series of holes in the paper make the mechanical piano/music box play the notes of a song

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Computer: a programmable computing device

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• Computer
  • What is a computer:

    Explanation:

    A computer is a computing device where the computing machinary is controlled by a series of instructions Furthermore: The serie of instructions can be changed !!!

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  • Example:

    With one series of instructions, the computer can compute the trajectory of a lunar mission With another series of instructions, the computer can compute the taxes of for a business person

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• Comment
  • I depicted the computer as a mechanical device above

  • In reality, the computer is an electronic device

  • To imagine how the electronical computer works, you need to:

    imagine that the roll of paper (containing the instructions) not only move forward but can also jump to an arbitrary position !!!