[Mashiro]

OpenVZ: Software virtualization based on the use of containers to isolated the VMs from each other. All resources are fully shared between all VMs and the host system and heavy overselling is possible. Vital and critical system processes are running on the host node and don't run inside the hosted VMs (hence why the OpenVZ VM memory usage is much lower vs KVM). Heavily crippled in regards of real world features (firewall modules are mostly disabled and only a small part can be enabled by the host node administrator for the VMs, no real virtual disk and filesystem and many other things). However this virtualization technology comes with tiny to no performance loss vs hardware virtualization like KVM.


KVM: Hardware virtualization that emulates a real machine inside a VM from BIOS to pretty much everything else. Resources here are / can be allocated to the VMs directly. However that doesn't mean that overselling is not possible. There are ways to still oversell KVM but not as much as OpenVZ. The memory usage is higher because every VM runs its own system processes because the VMs are fully isolated from each other and the host system. Like you'd be running several real servers. Due to hardware virtualization you can do whatever you want. No real limitations other than what the hardware, your knowledge and / or the ToS of the provider gives (you can even pass through GPUs, full CPUs with RAM and PCI/PCIe devices exclusively to VMs). For this price you pay with a small performance hit but with todays hardware it is hardly noticeable.


This question has been asked millions of times. Google probably has so many answers and maybe even more detailed and better answers than mine. My reply is just a brief OpenVZ vs KVM and their general / basic differences. I also wonder a bit... you have been here a long time and also on FreeVPS... and you ask this question now?