All virtualization systems used at the VPS market today can be divided into 2 major categories:

Process-level virtualization:
All virtual machines use the same OS kernel, and basically are isolated from each other. The way of virtualization is budget- wise and it also allows to automatically distribute dynamic resources of the server between Virtual machines.
The disadvantages:Virtual machines are not completely isolated, there’s a limited possibility for kernel tweaking ( as the kernel is shared between a few virtual machines), you can’t change the kernel version for any single virtual machine or download modules for a single virtual machine.
The most popular solutions here are open source OpenVZ and its commercial version Virtuozzo.

OS assisted virtualization:
A type of server virtualization technology which works at the OS layer. The physical server and single instance of the operating system is virtualized into multiple isolated partitions, where each partition emulates a real server. Each partition has its own OS with separate kernel. The asset of this method is a complete isolation of VM and the possibility to control the kernel and other parts inside the VM. The main disadvantage of this type of virtualization is the cost of implementation. Among the popular solutions here there are commercial VMware и Virtual PC and Open Source - Qemu, VirtualBox and KVM.

Paravirtualization appeared as a cost-effective variant of OS-level virtualization.

Xen is a paravirtualization solution used by Natcoweb for vps services. Xen virtualizes the processor and memory using a modified Linux kernel and virtualizes the I/O using custom guest OS device drivers.
Xen's support for virtual machine live migration from one host to another allows workload balancing and the avoidance of downtime.
In terms of resources Xen allows to deliver a guaranteed amount of CPU and RAM, thus making VPS services very close to the dedicated server in performance yet having the lower cost as the advantage.
Xen-based VPS plans can’t be oversold unlike OpenVZ or HyperVM, this technology allocates the ram that this vps has been configured for.
For our VPS clients we offer cPanel VPS Optimized and Dedikit control panel.
cPanel being in favor with the majority of clients is installed on Centos OS, while Dedikit panel is recommended for clients looking for Debian OS. Being a SAAS Dedikit allows to modify configuration files without the necessity to be installed on the server, thus making RAM consumption more effective.