Machine Language

1
Machine Language

• Computer hardware can process only a small number
  of primitive instructions
• arithmetical and logical operations
• program flow operations
• moving data between memory and the CPU
• Extremely difficult and tedius to write programs
  in machine code, but this was necessary before
  the invention of high-level languages (1950s).
• Each instruction in a high-level language (such
  as Javascript, Basic, C, C, Java, Python,
  Pascal) is translated into a sequence of machine
  language instructions.

2
John Von Neumann (1903-1957)

• Made deep contributions to
• quantum physics
• economics
• computer science
• hydrodynamics of explosions
• statistics
• game theory (pioneered MAD policy)
• and various areas of classical mathematics

3
John Von Neumann (1903-1957)

• On the Manhattan project, helped to work out the
  key ideas involved in thermonuclear reactions and
  the hydrogen bomb.
• At 29, an original member of IAS (the
  demigods).
• Pioneered the idea of a stored program
  computer. Before that, programming basically
  meant moving wires around.

4
Von Neumann Architecture

• Registers
• IR
• PC
• and more...

(RAM and ROM)
5
Fetch-Execute Cycle

• Fetch the next instruction
• Look in PC for location of next instruction, and
  copy that instruction into the IR.
• Decode the instruction
• Get data (if needed)
• Instruction specifies location of data to be
  used. Copy data to registers.
• Execute instruction

6
Simpletron
The Simpletron is a hypothetical computer
presented in the textbook Java How to Program
(by Deitel) for the purpose of explaining the
basic concept of machine language.

• 3 registers
• Accumulator
• Instruction register (IR)
• Program counter (PC)
• Instructions are 4-digit decimal numbers.
• Memory locations are numbered 00, 01, , 99.

7
I/O Instructions

• 10xx (READ)
• Read a number from the keyboard into memory
  location xx.
• 11xx (WRITE)
• Write a number from memory location xx onto the
  screen.

8
Load/Store Instructions

• 20xx (LOAD)
• Load a number from memory location xx into the
  accumulator.
• 21xx (STORE)
• Store a number from the accumulator into a memory
  location xx.

9
Arithmetic Instructions

• 30xx (ADD)
• Add a number from memory location xx
• to the number in the accumulator.
• 31xx (SUBTRACT)
• 32xx (DIVIDE)
• 33xx (MULTIPLY)

10
Transfer of Control Instructions

• 40xx (BRANCH)
• Copy xx into the program counter.
• 41xx (BRANCHNEG)
• Copy xx into the program counter if the number in
  the accumulator is negative.
• 42xx (BRANCHZERO)
• Copy xx into the program counter if the number in
  the accumulator is zero.
• 43xx (HALT)
• Terminate execution of the program.