What is a datacenter?
A datacenter is the primary container of inventory objects such as hosts and virtual machines. From the datacenter, you can add and organize inventory objects. Typically, you add hosts, folders, and clusters to a datacenter.
vCenter Server can contain multiple datacenters. Large companies might use multiple datacenters to represent organizational units in their enterprise.
What is a host?
A host is a computer that uses virtualization software to run virtual machines. Typically, a host is a computer running ESX or ESXi software.
Hosts provide the CPU and memory resources that the virtual machines use and give the virtual machines access to storage and networks. Multiple virtual machines can operate on the same host at the same time.
Adding a host to the vCenter Server allows you to manage it and the virtual machines that run on it.
What is a virtual machine?
A virtual machine is a software computer that, like a physical computer, runs an operating system and applications. An operating system installed on a virtual machine is called a guest operating system.
Every virtual machine has virtual devices that provide the same functionality as physical hardware. Virtual machines get CPU and memory, video cards, access to storage, and network connectivity from the hosts they run on.
In vSphere, virtual machines run on hosts or clusters. Multiple virtual machines can run on the same host or cluster at the same time.
What is virtual hardware?
Just as a physical computer has hardware devices such as CPU and memory, a virtual machine has virtual hardware devices. If you look at a virtual machine's configuration, you find virtual CPU, memory, hard disks, CD/DVD drives, floppy drives, Ethernet adapters, sound cards, and so on. Each virtual device performs the same function for the virtual machine as does the hardware on a physical computer.
Virtual hardware lets the virtual machine divide up the physical hardware as needed. For example, you can run many virtual machines on a single physical CPU, each appearing to have its own virtual CPU. You can move a virtual machine from one host to another and the mappings between the virtual and physical devices change automatically, while the virtual devices remain unchanged. Through virtual hardware, virtual machines are insulated from the details of physical hardware.
For a complete list of virtual devices, see the vSphere Web Client online help.
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