[CrashCourse CS] #7 The Central Processing Unit (CPU)

CPU : Central Processing Unit

• CPU's job is to execute programs.
• Programs are made up of a series of individual operations, called instructions, b/c they instruct computer what to do.
• Hypothetical example of an instruction table:
  
• The first 4 bit contains operation codes (opcodes), and the last four bit specify where the data for that operation should come from.
• ex) 0010 1110 at RAM address 0
  0010 : opcode (LOAD_A : Read RAM location into register A)
  1110 : data address (register the data in address 1110)
  
  

CPU Structure and Cycle

• Memory Registors (A, B, C, D) - temporarily store and manipulate vaules.
• Control Unit directs all of the different parts of the CPU.
  • Instruction Address Register - stores the memory address of the current instruction.
  • Instruction Register - stores the current instruction.
• Clock
  • Triggers an electrical signal at a precise and regular inerval.
  • Its signal is used by the Control Unit to advance the internal operation of the CPU.

1. Fetch Phase

• When we first boot up our computer, all of the registers start at 0.
• First phase of a CPU's operation - retrieve first instruction.

1. Instruction Address Register input 0 to RAM.
2. RAM returns the data stored in address 0, which is copied to the instruction register.

2. Decode Phase

• Figure out what the instructions is.
• Check instruction's OPcode with logic gates.

3. Execute Phase

• Perform instruction.
  
  

Clock Speed

• The speed at which a CPU can carry out each stop of the fetch - decode - execute cycle is called its Clock Speed.
  • Measured in Hertz, a unit of frequency.
  • 1 Hertz = 1 cycle per second.
• Today's CPU - Gigahertz : Billions of CPU cycles every single second.

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• Overclocking - modify the clock to speed up the tempo of the CPU.
  • CPUs are designed to handle a little bit of overclocking.
  • Too much can overheat or make errors.
• Underclocking - slowing the CPU down.
  • Saves power.
• Modern processors have Dynamic Frequency Scaling - change clock speed based on demand.

영어 표현

• ram : 들이받다.
• gobbledygook : language that is meaningless or is made unintelligible by excessive use of abstruse(=complex) technical terms; nonsense.
• beef up : strengthen, increase.

Thoughts

• CPU 파트가 처음엔 이해가 안돼서 여러번 돌려봤다. 그러니까 이해가 됬다.
• It is all about increasing the level of abstraction.