All our Virtual Servers run on hosts with eight Xeon cores, 16G RAM and a RAID-6 array of 15k rpm SAS disks. For some applications they actually out-peform dedicated servers.The virtualisation technology we use (Xen for Linux and MS Hyper-V for Windows) does not use shared memory (sometimes called burstable RAM). The physical memory you are allocated remains yours for the life of the virtual machine and is never allocated to somebody else's server.