Installation guide

CHAPTER 1 Introduction to VMware ESX Server
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inside a virtual machine) can never directly determine which specific underlying
physical resources they are accessing, such as which CPU they are running on in a
multiprocessor system or which physical memory is mapped to their pages. The
virtualization of the CPU incorporates direct execution: non-privileged instructions are
executed by the hardware CPU without overheads introduced by emulation.
The virtualization layer provides an idealized physical machine that is isolated from
other virtual machines on the system. It provides the virtual devices that map to
shares of specific physical devices; these devices include virtualized CPU, memory, I/O
buses, network interfaces, storage adapters and devices, human interface devices,
BIOS and others.
Each virtual machine runs its own operating system and applications; they cannot talk
to each other or leak data, other than via networking mechanisms similar to those
used to connect separate physical machines. This isolation leads many users of
VMware software to build internal firewalls or other network isolation environments,
allowing some virtual machines to connect to the outside while others are connected
only via virtual networks through other virtual machines.
CPU Virtualization
Each virtual machine appears to run on its own CPU, or set of CPUs, fully isolated from
other virtual machines, with its own registers, translation lookaside buffer, and other
control structures. Most instructions are directly executed on the physical CPU,
allowing compute-intensive workloads to run at near-native speed. Privileged
instructions are performed safely by the patented and patent-pending technology in
the virtualization layer.
Memory Virtualization
While a contiguous memory space is visible to each virtual machine, the physical
memory allocated may not be contiguous. Instead, noncontiguous physical pages are
remapped efficiently and presented to each virtual machine. Some of the physical
memory of a virtual machine may in fact be mapped to shared pages, or to pages that
are unmapped or swapped out. This virtual memory management is performed by
ESX Server without the knowledge of the guest operating system and without
interfering with its memory management subsystem.