Computing Architecture Continuum
From the mainframe to grid computing, each computing architecture has developed in response to the demands organizations place on their IT departments. Similar to the range of programming language options, each computing architecture in Figure 1 presents a unique environment.
Mainframe computers use a host/terminal architecture, whereby all of the application processing executes on the mainframe host. Multiple users can simultaneously access the mainframe via local or remote "dumb" terminals (or terminal emulation software), which simply display queries and results. Introduced in the 1950s, mainframes remain popular in large organizations needing extreme reliability, availability, and serviceability.
The mainframe is ideal for mission-critical applications that process bulk data such as credit-card processing, bank account management, market trading, and ERP. Applications that require high security are another mainframe strength. Today's leading mainframe vendors include IBM, Hewlett-Packard, and Unisys.
Minicomputers employ the same host/terminal architecture as mainframes but typically serve a smaller user population. Launched in 1959, the minicomputer era was ushered by Digital Equipment Corporation and the introduction of its PDP-1. Selling for an amazingly low $120,000, the PDP-1 extended the reach of computing to a broader audience.
Over time, minicomputers basically morphed into midrange systems and servers, but their function remains the same—processing applications for multiple users. In small and midsize businesses, midrange systems usually run general business applications. Large enterprises generally use them for department-level operations. Vendors include IBM, Hewlett-Packard, and Sun Microsystems.
Moving away from the hosting model, client/server architecture splits the application-processing load between one or more servers and the user's client computer. Client/server encourages IT departments to select the appropriate hardware and software platforms for client and server functions. For example, database management system servers frequently run on platforms specially designed and configured to perform queries, while file servers usually run on platforms with special elements for managing files.
Client/server was a response to monolithic, isolated applications running on minicomputers and mainframes. Seeking integrated, responsive, and comprehensive applications, companies turned to client/server architecture to support the complete range of their business processes—from call centers to CRM and beyond. Leading client/server vendors include Oracle and PowerSoft.
The Internet computing model defined by the World Wide Web introduced a new twist to client/server's distributed processing model. Whereas client/server relied on dedicated client-side software to run applications, Internet computing relies on one client application—the web browser—to present the GUIs of countless applications while back-end servers process the bulk of the application.
The shift from the client/server "fat client" to the Internet "thin client" brings huge benefits. Software upgrades are made solely at the server and no longer include a client-side component that has to be distributed to the user base. Meanwhile, applications both inside and outside the firewall give authorized users ready access to any web-enabled application, from company newsletters and HR benefits to e-commerce and financial services. Leading Internet vendors include Sun and BEA.
Grid computing architecture is emerging to let companies flatten the dominant three-tier Internet architecture. Today, the back end of a standard web application is processed by a low-end web server, a high-end application server, and a high-end database server or some other data store. Grids can meld the web server and application server tiers into a single tier of parallel, commodity servers running Linux.
A web application deployed on a grid architecture offers significant dollar savings over the same application running on three tiers. In different hardware configurations, grid computing is being used successfully on a variety of applications, from modeling financial markets and simulating earthquakes to serving millions of web pages per day. In the grid arena, the leading technologies are Linux and x86-based computers.
