For an introduction to server virtualization is the best suited of hypervisor from VMware - ESXi.

ESXi - standalone hypervisor from company VMware, which is the operating system (no console) that was created to run and manage virtual machines.
Standalone hypervisor - the operating system, which is installed on the server and allows you to create and run virtual machines
VMware ESX - the company is a hypervisor VMware, which, beginning with the fifth version of VMware vSphere is no longer available.
ESXi hypervisor free if used without the VMware vCenter server. After downloading the distribution site vmware.com you receive a key that activates a FREE license. And if you just install and use without having to enter a key, there will be a trial for 60 days. Restrictions on the number of virtual machines, as such, no. The fifth version of the hypervisor ESXi 5.0 and 5.1, there is a limit on the amount of virtual memory "on server" 32GB. You can install ESXi on an arbitrarily large number of servers and use them for commercial purposes, but in the free version, each server will be managed from a single console, technology will not work

Description in English.: VMware vSphere 5.1 delivers improved security along with many new features and enhancements that deliver unprecedented value to VMware customers. VMware vSphere 5.1 is based on the ESXi hypervisor architecture, a thin purpose-built hypervisor that does not depend on a general purpose operating system. In order to benefit from the unique capabilities and features of vSphere 5.1 VMware recommends that customers:
Migrate vSphere deployments running the earlier ESX architecture to the new ESXi hypervisor architecture
Upgrade older vSphere deployments to vSphere 5.1

INSTALLATION
Download the distribution to be written to disk, and then you are ready to install. Cause any difficulty setting should not. After it ended, we see that the system is properly installed in the server defined processor, amount of RAM, received DHCP network settings and offers to connect via http to download management tool.

FEATURES ESXI
After connecting to the ESXi host to obtain the following key features:
create a virtual machine (New Virual Machine)
create a Resource Pool (ability to configure the use of resources of the physical server, virtual machines)
connection to the SAN (storage system)