1. Introduction to Systems
   • What is a system?
   • Complexity makes building systems difficult.
2. Why is Complexity Bad?
   • Limits what we can build.
   • Causes lots of other problems.
3. Mitigating Complexity
   • We mitigate complexity with modularity and abstraction.
     • Modular systems are easier to reason about, manage, change, improve.
     • Modularity reduces fate-sharing.
     • Abstraction lets us specify interfaces without specifying implementation.
     • Good abstraction decreases the number of connections between modules.
4. Enforced Modularity
   • Soft modularity isn't enough.
   • One way to enforce is with a client/server model.
     • Reduces fate-sharing.
     • Important: remote procedure calls (RPCs) != procedure calls (PCs).
       1. Have to deal with different types of failure (network, server,..).
          • These failures are tricky, but starting with a modular design will let us reason about them and deal with them.
5. Other Goals
   • Beyond complexity, we might also want: scalability, fault-tolerance, security, performance, etc.
   • Starting with a good, modular design helps achieve these properties.
   • Difficult to get all at once; there are trade-offs.