Difference between revisions of "CSC103: DT's Notes 1"

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=CSC103 How Computers Work--Class Notes=
 
=CSC103 How Computers Work--Class Notes=
  
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The image on the left, above, shows an ''integrated circuit'' (IC)close up.  In reality the circuit is about as long as a quarter (and with newer technology even smaller).  The image on the right shows what is inside the IC.  Just 4 AND gates.  There are other ICs that contain different types of gates, such as OR gates or Inverters.
 
The image on the left, above, shows an ''integrated circuit'' (IC)close up.  In reality the circuit is about as long as a quarter (and with newer technology even smaller).  The image on the right shows what is inside the IC.  Just 4 AND gates.  There are other ICs that contain different types of gates, such as OR gates or Inverters.
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==Building a Two-Bit Adder with Logic Gates==
 
==Building a Two-Bit Adder with Logic Gates==
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To implement it with logic gates we make ''a'' and ''b'' inputs, and ''f'' the output of the circuit.  Then ''b'' is fed into an inverter gate (NOT), and the output of the inverter into the input of an AND gate.  The other input of the AND gate is connected to the ''a'' signal, and the output becomes ''f''.
 
To implement it with logic gates we make ''a'' and ''b'' inputs, and ''f'' the output of the circuit.  Then ''b'' is fed into an inverter gate (NOT), and the output of the inverter into the input of an AND gate.  The other input of the AND gate is connected to the ''a'' signal, and the output becomes ''f''.
 
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<center>[[Image:aANDNOTb.png|frame|A and Not B, D. Thiebaut, 2014, Released under the Creative Commons Attribution 2.0 Generic license.]]</center>
  
 
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<center>[[Image:2-bitAdderGates.png|frame|350px|2-Bit Adder, D. Thiebaut, 2014, Released under the Creative Commons Attribution 2.0 Generic license.]]</center>
 
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Let's assume that we want to play a very simple game based on ''coding''.  The game is quite easy to get: we want two people to have a conversation where each word or sentence that they can say is limited to a small set of preselected sentence, and each one is associated with a number.  When the two people talk to each other, they must pick the number corresponding to the sentence, question, or answer they want to say.
 
Let's assume that we want to play a very simple game based on ''coding''.  The game is quite easy to get: we want two people to have a conversation where each word or sentence that they can say is limited to a small set of preselected sentence, and each one is associated with a number.  When the two people talk to each other, they must pick the number corresponding to the sentence, question, or answer they want to say.
  
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[[File:Conversation.jpg|500px|right]]
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[[File:Conversation.jpg|thumb|500px|right|Daniel Coy, "Conversation", online image, https://flic.kr/p/7mWZpb, Captured July 2014.]]
  
 
Here's a list of numbers and their associated sentences:
 
Here's a list of numbers and their associated sentences:
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===Computer Memory===
 
===Computer Memory===
 
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<center>[[File:NandFlipFlop1.png|thumb|600px|Nand Flipflop 1, D. Thiebaut, 2014, Released under the Creative Commons Attribution 2.0 Generic license.]]</center>
 
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You may want to spend the time building it up with our [http://tinyurl.com/103applets| circuit simulator].  
 
You may want to spend the time building it up with our [http://tinyurl.com/103applets| circuit simulator].  
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<center>[[File:NandFlipFlop2.png|thumb|600px|Nand Flipflop 2, D. Thiebaut, 2014, Released under the Creative Commons Attribution 2.0 Generic license.]]</center>
 
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with similar circuits.
 
with similar circuits.
  
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<br /><center>[[File:Scale.gif|frame|Animated Scale, D. Thiebaut, 2014, Released under the Creative Commons Attribution 2.0 Generic license.]]</center>
 
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===The Processor===
 
===The Processor===
 
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[[Image:Calculator.png|right|250px]]
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[[Image:Calculator.png|right|thumb|300px|Ilnanny, "Calculator", online image, openclipart.org/image/800px/svg_to_png/170371/1338745223.png, captured Aug. 1st, 2014.]]
 
The processor has three important registers that allow it to work in this machine-like fashion: the '''PC''', the '''Accumulator''' (shortened to '''AC'''), and the '''Instruction Register''' ('''IR''' for short).  The PC is used to "point" to the address in memory of the next word to bring in.  When this number enters the processor, it must be stored somewhere so that the processor can figure out what kind of action to take.  This holding place is the '''IR''' register.  The way the '''AC''' register works is best illustrated by the way we use a regular hand calculator.  Whenever you enter a number into a calculator, it appears in the display of the calculator, indicating that the calculator actually holds this value somewhere internally.  When you type a new number that you want to add to the first one, the first number disappears from the display, but you know it is kept inside because as soon as you press the = key the sum of the first and of the second number appears in the display.  It means that while the calculator was displaying the second number you had typed, it still had the first number stored somewhere internally.  For the processor there is a similar register used to keep intermediate results.  That's the '''AC''' register.
 
The processor has three important registers that allow it to work in this machine-like fashion: the '''PC''', the '''Accumulator''' (shortened to '''AC'''), and the '''Instruction Register''' ('''IR''' for short).  The PC is used to "point" to the address in memory of the next word to bring in.  When this number enters the processor, it must be stored somewhere so that the processor can figure out what kind of action to take.  This holding place is the '''IR''' register.  The way the '''AC''' register works is best illustrated by the way we use a regular hand calculator.  Whenever you enter a number into a calculator, it appears in the display of the calculator, indicating that the calculator actually holds this value somewhere internally.  When you type a new number that you want to add to the first one, the first number disappears from the display, but you know it is kept inside because as soon as you press the = key the sum of the first and of the second number appears in the display.  It means that while the calculator was displaying the second number you had typed, it still had the first number stored somewhere internally.  For the processor there is a similar register used to keep intermediate results.  That's the '''AC''' register.
 
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[[File:PrintedCircuitBoard.jpg|250px | right]]
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[[File:PrintedCircuitBoard.jpg|250px|thumb|Barney Livingston, "BBC B - PCB, CPU removed," online image, farm1.staticflickr.com/83/235291503_080d9656a8_o_d.jpg, captured Aug. 1st, 2014.]]
 
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All the processor gets from these memory cells it reads are ''numbers''.  Remember, that's the only thing we can actually create in a computer: groups of bits.  So each memory cell's number is read by the processor.  How does the number move from memory to the processor?  The answer: on metal wires, each wire transferring one bit of the number.  If you have ever taken a computer apart and taken a look at its ''motherboard'', you will have seen such wires.  They are there for bits to travel back and forth between the different parts of the computer, and in particular between the processor and the memory.  The image to the right shows the wires carrying the bits (photo courtesy of [http://www.inkity.com/catalog/product/2/11195/Motherboard-Detail.html www.inkity.com]).  Even though it seems that some wires do not go anywhere, they actually connect to tiny holes that go through the motherboard and allow them to continue on the other side, allowing wires to cross each other without touching.).
 
All the processor gets from these memory cells it reads are ''numbers''.  Remember, that's the only thing we can actually create in a computer: groups of bits.  So each memory cell's number is read by the processor.  How does the number move from memory to the processor?  The answer: on metal wires, each wire transferring one bit of the number.  If you have ever taken a computer apart and taken a look at its ''motherboard'', you will have seen such wires.  They are there for bits to travel back and forth between the different parts of the computer, and in particular between the processor and the memory.  The image to the right shows the wires carrying the bits (photo courtesy of [http://www.inkity.com/catalog/product/2/11195/Motherboard-Detail.html www.inkity.com]).  Even though it seems that some wires do not go anywhere, they actually connect to tiny holes that go through the motherboard and allow them to continue on the other side, allowing wires to cross each other without touching.).
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===The Cookie Monster Analogy===
 
===The Cookie Monster Analogy===
 
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[[File:CookieMonsterPacMan.png|right|thumb|350px|Cookie Monster, D. Thiebaut, 2014, Released under the Creative Commons Attribution 2.0 Generic license.]]
 
The processor is just like the cookie monster.  But a cookie monster acting like Pac-Man, a Pac-Man that follows  
 
The processor is just like the cookie monster.  But a cookie monster acting like Pac-Man, a Pac-Man that follows  
 
a straight path made of big slabs of cement, where there's a cookie on each slab.  Our Cookie-Monster-Pac-Man  
 
a straight path made of big slabs of cement, where there's a cookie on each slab.  Our Cookie-Monster-Pac-Man  
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===Instructions and Assembly Language===
 
===Instructions and Assembly Language===
 
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Latest revision as of 14:24, 7 September 2017

--© D. Thiebaut 2012, 2013, 2014
Last revised --D. Thiebaut (talk) 08:05, 9 October 2013 (EDT)


Newer Version, 2014



CSC103 How Computers Work--Class Notes


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