System information

CPU, Memory, and Network Virtualization
A VMware virtual machine provides complete hardware virtualization. The guest operating system and
applications running on a virtual machine can never determine directly which physical resources they are
accessing (such as which physical CPU they are running on in a multiprocessor system, or which physical
memory is mapped to their pages).
The following virtualization processes occur.
CPU virtualization
Each virtual machine appears to run on its own CPU (or a set of CPUs), fully
isolated from other virtual machines. Registers, the translation lookaside
buffer, and other control structures are maintained separately for each virtual
machine.
Most instructions are executed directly on the physical CPU, allowing resource-
intensive workloads to run at near-native speed. The virtualization layer safely
performs privileged instructions.
Memory virtualization
A contiguous memory space is visible to each virtual machine. However, the
allocated physical memory might not be contiguous. Instead, noncontiguous
physical pages are remapped and presented to each virtual machine. With
unusually memory-intensive loads, server memory becomes overcommitted.
In that case, some of the physical memory of a virtual machine might be
mapped to shared pages or to pages that are unmapped or swapped out.
ESX/ESXi performs this virtual memory management without the information
that the guest operating system has and without interfering with the guest
operating system’s memory management subsystem.
Network virtualization
The virtualization layer guarantees that each virtual machine is isolated from
other virtual machines. Virtual machines can communicate with each other
only through networking mechanisms similar to those used to connect separate
physical machines.
The isolation allows administrators to build internal firewalls or other network
isolation environments that allow some virtual machines to connect to the
outside, while others are connected only through virtual networks to other
virtual machines.
Storage Virtualization
ESX/ESXi provides host-level storage virtualization, which logically abstracts the physical storage layer from
virtual machines. Virtual machines running on the ESX/ESXi host are not aware of the complexities and
specifics of the storage devices to which the host connects.
An ESX/ESXi virtual machine uses a virtual hard disk to store its operating system, program files, and other
data associated with its activities. A virtual disk is a large physical file, or a set of files, that can be copied,
moved, archived, and backed up as easily as any other file. You can configure virtual machines with multiple
virtual disks.
To access virtual disks, a virtual machine uses virtual SCSI controllers. These virtual controllers appear to a
virtual machine as different types of controllers, including BusLogic Parallel, LSI Logic Parallel, LSI Logic SAS,
and VMware Paravirtual. These controllers are the only types of SCSI controllers that a virtual machine can
see and access.
Chapter 1 Overview of VMware ESX/ESXi
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