Virtual Machine: Guest and Consumer of ESXi Host

You can use virtualization to consolidate and run multiple workloads as VMs on a single
computer.

In traditional architectures, the operating system interacts directly with the installed hardware. The
operating system schedules processes to run, allocates memory to applications, sends and receives
data on network interfaces, and both reads from and writes to attached storage devices.

In comparison, a virtualized host interacts with the installed hardware through a thin layer of
software called the virtualization layer or hypervisor.

The hypervisor provides physical hardware resources dynamically to VMs as needed to support
the operation of the VMs. With the hypervisor, VMs can operate with a degree of independence
from the underlying physical hardware. For example, a VM can be moved from one physical host
to another. In addition, its virtual disks can be moved from one type of storage to another without
affecting the functioning of the VM.

Physical Resource Sharing

With virtualization, you can run multiple VMs on a single physical host, with each VM sharing
the resources of one physical computer across multiple environments. VMs share access to CPUs
and are scheduled to run by the hypervisor.
In addition, VMs are assigned their own region of memory to use and share access to the physical
network cards and disk controllers. Different VMs can run different operating systems and
applications on the same physical computer.
When multiple VMs run on an ESXi host, each VM is allocated a portion of the physical
resources. The hypervisor schedules VMs like a traditional operating system allocates memory
and schedules applications. These VMs run on various CPUs. The ESXi hypervisor can also
overcommit memory. Memory is overcommitted when your VMs can use more virtual RAM than
the physical RAM that is available on the host
VMs, like applications, use network and disk bandwidth. However, VMs are managed with
elaborate control mechanisms to manage how much access is available for each VM. With the default resource allocation settings, all VMs associated with the same ESXi host receive an equal
share of available resources.