# What is System Design? — System Design

Source: https://www.geekswithgeeks.com/en/system-design/sd-intro

> Defining components, data, and their interactions to meet goals.

## The definition

System design is deciding the **architecture, components, interfaces, and data** of a system so it meets its functional and non-functional goals — like scale, latency, and availability.

## Functional vs non-functional

**Functional**: what the system does (post a tweet, place an order). **Non-functional**: how well it does it (99.9% uptime, p99 < 200ms, 10k writes/sec).

## City planning

Designing a system is like planning a city: roads (network), power (compute), water (data), and zoning rules (constraints). You can't retrofit a highway easily — plan the load first.

## Start with requirements

In an interview, never jump to boxes and arrows. Spend the first few minutes clarifying scope, users, and scale — the design flows from there.