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= Containers versus Virtual Machines =
This article gives an overview of containers for those who know what a Virtual Machine (VM) is. VMs are implemented by products such as VMware, , Parallels, Xen, Hyper-V, Virtual Box, Parallels Desktop etc. If you do not have experience with those or similar products, better read [[../What are containers/]] whitepaper.
Containers are very similar to VMs in a sense that they also let one to partition one physical computer into multiple small isolated partitions (called VMs or containers).
Xen, KVM, VMware and other hypervisor-based products provide an ability to have multiple instances of virtual hardware (called VMs – Virtual Machines) on a single piece of real hardware. On top of that virtual hardware one can run any Operating System, so it's possible to run multiple different OSs on one single server. Each VM runs full software stack (including an OS kernel).
In contrast, OpenVZ and containers technology uses a single-kernel approach. There is only one single OS kernel running, and on top of that there are multiple isolated instances of user-space programs. This approach is more lightweight than VM. The consequences are:
# Waiving the need to run multiple OS kernels leads to results in '''higher density''' of containers (compared to VMs)
# Software stack that lies in between an application and the hardware is much thinner, this means '''higher performance''' of containers (compared to VMs)
* there is no I/O overhead (for VMs it can be as high as 1.5x to 3x, especially for small requests)
* mass deployment is easy
== Networking ==
== Memory management ==
== Density ==
There is a separate article which explains differences in technologies and why containers are better in high density environments [[WP/Containers density]].
== Performance ==
FIXME: link to performance paper