System Design Fundamentals

System Design is the process of planning how a software system should work before building it. Think about constructing a large building. Before workers start putting up walls, architects decide where the rooms, elevators, electricity, water systems, emergency exits, and entrances should go. Software works in a similar way. When developers build applications such as Amazon, Instagram, Netflix, Uber, or WhatsApp, they cannot simply start writing code and hope everything works. They first need to decide how millions of users, servers, databases, files, and requests will work together. A simple way to remember it is: System Design = The blueprint of a software system. What Do We Decide in System Design? During system design, engineers make decisions about things such as: How users connect to the application Where information is stored How different parts of the application communicate How images and videos are stored How the system handles millions of users How the application stays fast How failures are handled How user information stays secure For example, imagine designing WhatsApp. A user sends a message. That message must travel to WhatsApp's servers, reach the correct person, possibly be stored temporarily, appear on multiple devices, and trigger a notification. If millions of people send messages at the same time, the system must continue working without becoming extremely slow or crashing. That planning is system design. Why Does System Design Matter? A good software system should be: Fast Reliable Secure Scalable Affordable to operate Easy to maintain Imagine Instagram without good system design. Millions of users might open the application at the same time. Servers could become overloaded, photos might take several seconds to load, comments could disappear, and the application might frequently crash. System design helps engineers prepare for these situations before they become major problems. System Design in Software Interviews System design is also common i