d>Numbers where the left most bit is the sign bit.</td>
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    <td><strong>Simulator </strong></td>
    <td>Computer software that models reality in some way. Virtual reality aims 
      to make the simulation so realistic that it seems real. Most simulations 
      are designed to be useful rather than realistic.</td>
  </tr>
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    <td><strong>Source Code</strong></td>
    <td>The human readable program code typed into the computer. See executable 
  