As a domain expert in virtualization technology, I'd like to clarify the relationship between vSphere and ESXi. They are not the same but are closely related components of VMware's virtualization ecosystem.
vSphere is a suite of products that provides a comprehensive platform for managing virtual infrastructure. It includes several components such as vCenter Server, vSphere Client, and vSphere Web Client, which are used for centralized management of virtual machines and ESXi hosts.

On the other hand, ESXi, which stands for Elastic Sky X hypervisor, is a type of hypervisor that is installed directly on a physical machine, also known as a host. It is the core virtualization component that allows multiple virtual machines to run on a single physical server. ESXi is designed to be a minimal-footprint, high-performance hypervisor that is optimized for enterprise environments.

The vCenter Server is a centralized management application that plays a pivotal role in the vSphere suite. It enables administrators to manage multiple ESXi hosts from a single interface. This includes provisioning, monitoring, and maintaining virtual machines across the hosts. The vCenter Server also provides advanced features like distributed resource scheduling, which allows for more efficient allocation of resources across the data center.

The vSphere Client is a tool used to access and interact with the vCenter Server. It provides a graphical user interface for managing the virtual infrastructure. Administrators can use the vSphere Client to perform tasks such as creating and configuring virtual machines, monitoring host and virtual machine performance, and managing storage and networking resources.

In essence, while ESXi is the hypervisor that provides the virtualization capabilities, vSphere is the broader suite of products that includes the management tools necessary to operate and maintain a virtualized environment. The two are often used together, with ESXi hosts being managed through the vSphere suite, but they serve distinct roles within the virtualization stack.

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VMware vCenter server is a centralized management application that lets you manage virtual machines and ESXi hosts centrally. vSphere client is used to access vCenter Server and ultimately manage ESXi servers. ... vSphere is a product suite, ESXi is a hypervisor installed on a physical machine.Aug 24, 2012read more >>