Information Representation: Machine Instructions Demo

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Information Representation Machine
Instructions Demo
Department of Computer and Information
Science,School of Science, IUPUI
CSCI 230
Dale Roberts, Lecturer IUPUI droberts_at_cs.iupui.edu
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xComputer Applet

• xComputer applet a java applet that simulates a
  simple model computer (which is also called
  xComputer). The model computer is discussed in
  Chapter 3 of The Most Complex Machine. The
  xComputer consists of a Central Processing Unit
  (CPU) and a main memory that holds 1024
  sixteen-bit binary numbers. The CPU contains an
  Arithmetic-Logic Unit (ALU) for performing basic
  arithmetic and logical computations. It also
  contains eight registers, which hold binary
  numbers that are being used directly in the CPU's
  computations, a Control circuit, which is
  responsible for supervising the computations that
  the CPU performs, and a clock, which drives the
  whole operation of the computer by turning its
  single output wire on and off.

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xComputer Instructions

• xComputer uses 16 bits per instruction. 6 bits
  are dedicated to the opcode, leaving 10 bits for
  the operand.
• The type of information stored in the operand is
  dependent on the instruction being executed.
• A listing of xComputer opcodes can be found at
  http//www.cs.iupui.edu/aharris/n301/xMachine.htm
  l.
• The xComputer applet can be run from
  http//www.cs.iupui.edu/aharris/n301/alg/tmcm-jav
  a-labs/labs/xComputerLab1.html.

• xComputer uses 16 bits per instruction. 6 bits
  are dedicated to the opcode, leaving 10 bits for
  the operand.
• The type of information stored in the operand is
  dependent on the instruction being executed.
• A listing of xComputer opcodes can be found at
  http//www.cs.iupui.edu/aharris/n301/xMachine.htm
  l.
• The xComputer applet can be run from
  http//www.cs.iupui.edu/aharris/n301/alg/tmcm-jav
  a-labs/labs/xComputerLab1.html.

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Sample Opcodes
(12) refers to the contents of address 12
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Semantic Gap

• Machine languages Native tongue of a particular
  kind of computer. Each instruction is a binary
  string. The code is used to indicate operations
  to be performed and the memory cells to be
  addressed. This form is the easiest form for
  computers to understand, but is the most
  difficult for a person to understand.
• Assembly languages Again, specific to one type
  of computer. Uses descriptive names for
  operations and data, e.g. LOAD value, ADD
  delta, Store value. Assemblers translate this
  to machine language. Intermediate level.
  Somewhat descriptive, but basically follow the
  machine instructions.
• High-level languages Write program instructions
  called statements that resemble a limited version
  of English. e.g. value value delta.
  Portable, meaning it can be used on different
  types of computers without modification.
  Compilers translate them to machine languages.
  Example are Fortran, Pascal, COBOL, C, C,
  Basic, etc.
• Semantic gap between statements in a high-level
  language and machine/assembly language. Each
  high level statement may represent many hundreds
  of machine instructions. Compilers must bridge
  this gap.
• Complex machine instruction computer try to
  reduce this gap by implementing high-level
  language opcodes. This diminishes the semantic
  gap but makes the machine instructions more
  complex, and therefore makes the CPU circuitry
  more complex.

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Real-life Example Pentium 4.

• The instruction set information for the Pentium 4
  process can be found at ftp//download.intel.com/d
  esign/Pentium4/manuals/25366520.pdf.

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Pentium 4 ADD

• DescriptionAdds the first operand (destination
  operand) and the second operand (source operand)
  and stores the result in the destination operand.
  The destination operand can be a register or a
  memory location the source operand can be an
  immediate, a register, or a memory location.
  (However, two memory operands cannot be used in
  one instruction.) When an immediate value is used
  as an operand, it is sign-extended to the length
  of the destination operand format. The ADD
  instruction performs integer addition. It
  evaluates the result for both signed and unsigned
  integer operands and sets the OF and CF flags to
  indicate a carry (overflow) in the signed or
  unsigned result, respectively. The SF flag
  indicates the sign of the signed result. This
  instruction can be used with a LOCK prefix to
  allow the instruction to be executed atomically.
• OperationDEST ? DEST SRC
• So you can see that the instructions are a little
  more complicated in real life than in xComputer.
  But the same principles apply.

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Pentium 4 Add (cont)
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Acknowledgements

• Several graphics and terms were obtained from
  Jonathan Michael Auld Central Queensland
  University.
• xComputer and its machine instructions were
  developed by David Eck.