A **server** is a [[Computer|computer]] or [[Software|software system]] that provides services, resources, or data to other computers or programs, known as [[Client (computing)|clients]], typically over a [[Computer network|network]]. In the [[Client–server model|client–server model]], the server responds to requests initiated by clients, which may be other computers, [[Application software|applications]], or devices seeking to access shared resources or functionality. Servers are foundational components of modern [[IT infrastructure|IT infrastructure]] and underpin virtually all networked computing environments, from small business systems to global internet services and [[Cloud computing|cloud]] platforms. The term server refers both to the physical or virtual hardware on which server software runs and to the software itself. Physical servers are typically high-reliability machines designed for continuous operation, equipped with redundant [[Power supply|power supplies]], [[Error-correcting code memory|error-correcting memory]], and multiple [[Network interface controller|network interfaces]], and housed in [[Data center|data centers]] in [[Rack server|rack-mounted]] or [[Blade server|blade]] form factors. [[Virtual machine|Virtual servers]], created through [[Hypervisor|hypervisors]] such as [[VMware vSphere|VMware]], [[Microsoft Hyper-V|Hyper-V]], and [[Kernel-based Virtual Machine|KVM]], allow multiple server instances to run on a single physical machine, improving resource utilization and operational flexibility. [[Cloud computing|Cloud]] providers including [[Amazon Web Services|AWS]], [[Microsoft Azure|Azure]], and [[Google Cloud Platform|Google Cloud]] offer servers as on-demand [[Infrastructure as a service|infrastructure-as-a-service]] (IaaS) resources, provisioned and managed programmatically. Servers are categorized by the specific services they provide. **[[Web server|Web servers]]** such as [[Apache HTTP Server|Apache]] and [[Nginx]] serve [[Hypertext Transfer Protocol|HTTP]] content to browsers and applications. **[[Database server|Database servers]]** host [[Database management system|database management systems]] such as [[MySQL]], [[PostgreSQL]], and [[Microsoft SQL Server|SQL Server]]. **[[File server|File servers]]** provide shared access to stored files across a network. **[[Mail server|Mail servers]]** manage the sending, receiving, and storage of [[Email|email]]. **[[Application server|Application servers]]** execute [[Business logic|business logic]] for multi-tier applications. **[[DNS server|DNS servers]]** resolve [[Domain name|domain names]] to [[IP address|IP addresses]]. **[[Proxy server|Proxy servers]]** and **[[Reverse proxy|reverse proxies]]** intermediate between clients and backend services for purposes including [[Load balancing (computing)|load balancing]], [[Caching|caching]], and [[Transport Layer Security|TLS]] termination. The boundaries between these categories have blurred with the rise of [[Microservices|microservices]] architectures, in which discrete server processes fulfill highly specific functions and communicate over lightweight [[Application programming interface|APIs]].