What is Citrix server?

Citrix MetaFrame Presentation Server is a technology that can allow remote users to connect to applications that are actually installed on a remote computer. It uses a mix of technology that results in that remote application looking and behaving just as though it was installed on the local machine.

It’s a server solution that uses Microsoft Terminal Services software to deliver Windows applications to PCs, Apple Macintosh computers, X terminals and UNIX workstations. This enables users of those systems to access and use those programs which are available to those using the Windows operating system. Citrix servers use two technologies; WinFrame and Independent Computing Architecture (ICA).

ICA

Short for Independent Computing Architecture, ICA is a protocol designed specifically for transmitting Windows graphical display data as well as keyboard and mouse input over a network. ICA is one of two technologies used by Citrix servers, the other being WinFrame.

WinFrame

A technology developed by Citrix Systems that turns Windows NT into a multi-user operating system. Together with another Citrix technology called ICA, WinFrame enables a Windows NT server to function like a minicomputer. The result is that network users on non-Windows machines (e.g., Macintoshes, DOS systems, and UNIX machines) can run Windows applications. The actual applications are executed on the WinFrame Application Server; the client machines are just terminals, used only for entering user input and displaying application output.
The ICA protocol is responsible for sending input and output between the client machines and the WinFrame server. Conceptually, the protocol is similar to X-Window, which serves the same purpose for UNIX systems.