VMware ESXi Server is an enterprise-level virtualization product offered by VMware, Inc. VMware call ESXi a bare metal hypervisor as it becomes the server OS. There is no need to load any other server operating system.

The base ESXi Server product is Free, yes Free. Support and added features are billable. Added features include high availability, load balancing, and consolidated backup.

VMware ESXi can be obtained in one of two ways.

1. It can come embedded in a new server. It is actually in a flash chip inside it is not installed on the hard drive.

2. You can download the ESXi installer from VMware.com

Microsoft's ISA Server (Internet Security and Acceleration Server) is the successor to Microsoft's Proxy Server 2.0 (see proxy server) and is part of Microsoft's .NET support. ISA Server provides the two basic services of an enterprise firewall and a Web proxy/cache server. ISA Server's firewall screens all packet-level, circuit-level, and application-level traffic. The Web cache stores and serves all regularly accessed Web content in order to reduce network traffic and provide faster access to frequently-accessed Web pages. ISA Server also schedules downloads of Web page updates for non-peak times.

ISA Server allows administrators to create policies for regulating usage based on user, group, application, destination, schedule, and content type criteria. ISA Server is designed to work with Windows 2000and later operating systems and to take advantage of Windows' Kerberos security. ISA Server includes a software development kit (SDK).

ISA Server comes in two editions, Standard Edition and Enterprise Edition. Standard Edition is a stand-alone server that supports up to four processors. Enterprise Edition is for large-scale deployments, server array support, multi-level policy, and computers with more than four processors. Licenses are based on the number of processors.