Evolution of cloud computing Progressed from mainframe → distributed systems → cluster → grid → utility computing → virtualization → Web 2.0, culminating in today’s cloud services. Definition & service models Cloud computing = on‑demand delivery of IT resources (servers, storage, apps, etc.) over the Internet. Core service categories: IaaS (virtual machines), PaaS (managed development platforms), SaaS (ready‑to‑use applications). Deployment models Public cloud – third‑party hosted (AWS, Azure, GCP). Private cloud – dedicated to a single organization. Hybrid cloud – mix of public & private for flexibility. Community cloud – shared by organizations with common requirements (e.g., healthcare, education). Centralized vs. distributed systems Centralized: single control point, hierarchical, easier management but a single point of failure. Distributed: multiple autonomous nodes, decentralized control, higher scalability and fault tolerance. Pros & cons of cloud computing Advantages: cost savings, pay‑as‑you‑go, data redundancy, scalability, high availability, flexibility. Disadvantages: reliance on internet connectivity, security & privacy concerns, reduced direct control over infrastructure.