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