In case of VMs, every guest operating system kernel "thinks" it is managing some hardware, including memory (RAM). It performs memory allocation, accountingand so on. FIXME: describe memory sharing, balooning, swap through slow I/O etc. FIXME what else? In contrast, containers' memory is managed by a single entity -- the kernel. Therefore:* there is no need for balooning;* sharing memory pages between containers is trivial;* there is no need to preallocate the memory for a CT when it starts -- memory is allocated on demand;* swapping is as fast as on a usual non-virtualized system. In addition, latest version of OpenVZ kernel (based on RHEL6) is using VSwap technology. VSwap simplifies memory management FIXME