VMware ESXi 3.5 is the latest generation of the bare-metal x86 hypervisor that VMware pioneered and introduced over seven years ago. The industry’s thinnest hypervisor, ESXi is built on the same technology as VMware ESX, so it is powerful enough to run even the most resource-intensive applications; however, it is only 32 MB in size and runs independently of a general-purpose OS.
The following table shows just how much smaller the VMware EXSi installed footprint is compared to other hypervisors. These are results from installing each product and measuring disk space consumed, less memory swap files.
Comparative Hypervisor Sizes (including management OS)
VMware ESX 3.5 2GB VMware ESXi 32MB Microsoft Hyper-V with Windows Server 2008 10GB Microsoft Hyper-V with Windows Server Core 2.6GB Citrix XenServer v4 1.8GB
As the numbers show, ESXi has a far smaller footprint than competing hypervisors from vendors that like to label ESX as "monolithic."
The ESXi architecture contrasts sharply with the designs of Microsoft Hyper-V and Xen, which both rely on a general-purpose management OS – Windows Server 2008 for Hyper-V and Linux for Xen – that handles all management and I/O for the virtual machines.
See the rest on VMware's blog: Virtual Reality