The VMware vSphere software suite delivers an industry-leading virtualization platform to provide application virtualization within a highly available, resilient, efficient on-demand infrastructure. ESXi and vCenter are components of the vSphere software suite. ESXi is a hypervisor installed directly onto a physical server node, enabling it to be partitioned into multiple virtual machines (VMs). VMware vCenter server is a centralized management application that is used to manage the ESXi hosts and VMs.

vCenter Server is the centralized console for managing a VMware environment. It is the primary point of management for both server virtualization and vSAN. vCenter Server is the enabling technology for advanced capabilities such as VMware vSphere vMotion, VMware vSphere Distributed Resource Scheduler (DRS), and VMware vSphere High Availability (HA). vCenter supports a logical hierarchy of data centers, clusters, and hosts, which allows resources to be separated by use cases or lines of business and allows resources to move dynamically as needed. This is all performed from a single interface.

VMware ESXi is an enterprise-class hypervisor that deploys and services VMs. Figure 38 illustrates the basic ESXi architecture. 

Figure 38.    vSphere ESXi architecture

ESXi partitions a physical server into multiple secure, portable VMs that can run side by side on the same physical server. Each VM represents a complete system with processors, memory, networking, storage, and BIOS. Guest operating systems and software applications can be installed and run in the VM without requiring modification. 

The hypervisor provides physical-hardware resources dynamically to VMs as required to support the operation of the VMs. The hypervisor enables VMs to operate with a degree of independence from the underlying physical hardware. For example, a VM can be moved from one physical host to another. Also, the VM’s virtual disks can be moved from one type of storage to another without affecting the functioning of the VM. 

ESXi also isolates VMs from one another. When a guest operating system on a host fails, other VMs on the same physical host are unaffected and continue to run. VMs share access to CPUs and the hypervisor is responsible for CPU scheduling. In addition, ESXi assigns VMs a region of usable memory and provides shared access to the physical network cards and disk controllers associated with the physical host. Different VMs can run different operating systems and applications on the same physical system.