Intro to C

Great idea in Computer Architecture

1. Abstraction

  • (Layers of Representation/Interpretation)

2. Moore’s Law（摩尔定律）

3. Principle of Locality/Memory Hierarchy（局部性和内存层次性原则）

4. Parallelism（并行）

  • 加速频繁事件（Amdahl’s law）

5. Performance Measurement & Improvement

6. Dependability via redundancy（冗余实现可靠性）

  • RAID…

  • 失去一个数据中心，但是整个网络不会宕机

Compiled & Interpreted（编译和解释）

  • Translation happens in two ways
    ○ Compilation
    ○ Interpretation
    ○ Some languages use both!

  • C compilers map C programs directly into architecture-specific machinecode (string of 1s and 0s)

  • Java converts to architecture-independent bytecode which is then compiled by a just-in-time (JIT) compiler.

  • Python environments converts to Python bytecode at runtime instead of at compile-time.

    • Runtime versus JIT compilation differ in when the program is converted to low-level assembly language that is eventually translated into machine code.

  • With C, there is generally a 3-part process in handling a .c file

    • .c files are compiled into .s files ⇒ compilation by the compiler
    • .s files are assembled into .o files ⇒ assembly by the assembler (this step is generally hidden, so most of the time we directly convert .c files into .o files)
    • .o files are linked together to create an executable ⇒ linking by the linker

编译的优点和缺点

  • 优点

    • 很好的运行时表现(because it optimizes for a given architecture)

  • 缺点

    • 依赖特定的硬件平台
    • 在新系统上必须重新 build
    • “Change → Compile → Run [repeat]” iteration cycle can be slow during development
      • but make only rebuilds changed pieces, and can compile in parallel: make -j
      • linker is sequential though → Amdahl’s Law