Esxi Hypervisor

Virtual Machine (VM) is software that is an implementation of the hardware that executes programs like the hardware. VM is divided into two by the use and degree of correspondence on a real device. Programs that provide virtualization called hypervisor. Hypervisor can work on a bare machine called virtual machines or run natively on an operating system. Vmware ESXi is one virtual machine software that works on a bare machine.

Vmware ESXi 1.3 FeaturesVMware ESXi has the following features:
1. 64-bit architecture can improve the performance and supports up to 1TB of physical RAM on the host.
2. Performance optimization for virtual workloads. VMware ESX and ESXi 4.0 has been optimized for performance of certain critical business applications such as Oracle Database Server, Microsoft SQL, and Microsoft Exchange.
3. Support for virtual machines are bigger and stronger. Can run at up to 64 physical systems Core CPU, 256 virtual CPU, 1TB RAM, and up to hundreds of virtual machines on a host.Configure virtual machine with 255GB of RAM.
4. Support for eight-way virtual SMP.VMware Virtual Symmetric Multiprocessing (SMP) to improve virtual machine performance by enabling a single virtual machine to use up to eight physical processors, simultaneously.VMware Virtual SMP enables virtualization of the most CPU-intensive enterprise applications such as databases, ERP and CRM.
5. VMsafe ™ VMware.VMware VMsafe is a new security technology that helps protect virtualized workloads in ways previously not possible with physical machines. VMsafe provides a set of security APIs that third-party security mengaktifkanproduk to obtain the same visibility as VMware ESX or ESXi virtual machine into operation. Architecture
Vmware ESXi has the architecture as follows:
1. Bare-metal, 64-bit hypervisor architectureMade as small as possible so as there is no OS that works. Working directly on the server and requires no operating system on the host.
2. Virtual disk fileUsing the virtual machine disk (VMDK) to provide access to private datastore, so users are free to create, manage and migrate into the virtual.


Virtual Network 3.2.3
Virtual networking capabilities in VMware ESXi and ESX allows users to build complex network between virtual machines residing on a single host or in some installations VMware ESXi and ESX host. Configure each virtual machine with one or more virtual NICs, each with its own IP and MAC address, to create a virtual machine can be indistinguishable from physical machines.


I think this is very good hypervisor software. 
Pro:
1. Esxi is a bare metal hypervisor that optimized your resources.
2. With a less services like windows, esxi reduced memory usage and minimalized  crash  system. It's very good use for server.
3. Esxi have physical to virtual converter service so you can virtualized your server without made it from zero.
4. Money,power,and resources efficiency.\
5. remote access
6. provide virtual network


I believe Exsi is good for server.


More reading  http://www.vmware.com/products/esxi/