Purpose and OriginSince 1994 mainframes have been combined with distributed architectures to provide massive storage and to improve system security, flexibility, scalability, and reusability in the client/server design. In a mainframe server software architecture, mainframes are integrated as servers and data warehouses in a client/server environment. Additionally, mainframes still excel at simple transaction-oriented data processing to automate repetitive business tasks such as accounts receivable, accounts payable, general ledger, credit account management, and payroll. Siwolp and Edelstein provide details on mainframe server software architectures see [Siwolp 95, Edelstein 94].
Technical DetailWhile client/server systems are suited for rapid application deployment and distributed processing, mainframes are efficient at online transactional processing, mass storage, centralized software distribution, and data warehousing [Data 96]. Data warehousing is information (usually in summary form) extracted from an operational database by data mining (drilling down into the information through a series of related queries). The purpose of data warehousing and data mining is to provide executive decision makers with data analysis information (such as trends and correlated results) to make and improve business decisions.
a mainframe in a three tier client/server architecture. The combination of mainframe horsepower as a server in a client/server distributed architecture results in a very effective and efficient system. Mainframe vendors are now providing standard communications and programming interfaces that make it easy to integrate mainframes as servers in a client/server architecture. Using mainframes as servers in a client/server distributed architecture provides a more modular system design, and provides the benefits of the client/server technology.
Using mainframes as servers in a client/server architecture also enables the distribution of workload between major data centers and provides disaster protection and recovery by backing up large volumes of data at disparate locations. The current model favors "thin" clients (contains primarily user interface services) with very powerful servers that do most of the extensive application and data processing, such as in a two tier architecture. In a three tier client/server architecture, process management (business rule execution) could be off-loaded to another server.
Usage ConsiderationsMainframes are preferred for big batch jobs and storing massive amounts of vital data. They are mainly used in the banking industry, public utility systems, and for information services. Mainframes also have tools for monitoring performance of the entire system, including networks and applications not available today on UNIX servers [Siwolp 95].
New mainframes are providing parallel systems (unlike older bipolar machines) and use complementary metal-oxide semiconductor (CMOS) microprocessors, rather than emitter-coupler logic (ECL) processors. Because CMOS processors are packed more densely than ECL microprocessors, mainframes can be built much smaller and are not so power-hungry. They can also be cooled with air instead of water [Siwolp 95].
While it appeared in the early 1990s that mainframes were being replaced by client/server architectures, they are making a comeback. Some mainframe vendors have seen as much as a 66% jump in mainframe shipments in 1995 due to the new mainframe server software architecture [Siwolp 95].
Given the cost of a mainframe compared to other servers, UNIX workstations and personal computers (PCs), it is not likely that mainframes would replace all other servers in a distributed two or three tier client/server architecture.
MaturityMainframe technology has been well known for decades. The new improved models have been fielded since 1994. The new mainframe server software architecture provides the distributed client/server design with massive storage and improved security capability. New technologies of data warehousing and data mining data allow extraction of information from the operational mainframe server's massive storage to provide businesses with timely data to improve overall business effectiveness. For example, stores such as Wal-Mart found that by placing certain products in close proximity within the store, both products sold at higher rates than when not collocated.1
Costs and LimitationsBy themselves, mainframes are not appropriate mechanisms to support graphical user interfaces. Nor can they easily accommodate increases in the number of user applications or rapidly changing user needs [Edelstein 94].
AlternativesUsing a client/server architecture without a mainframe server is a possible alternative. When requirements for high volume (greater than 50 gigabit), batch type processing, security, and mass storage are minimal, three tier or two tier architectures without a mainframe server may be viable alternatives. Other possible alternatives to using mainframes in a client/server distributed environment are using parallel processing software architecture or using a database machine.
Complementary TechnologiesA complementary technology to mainframe server software architectures is open systems . This is because movement in the industry towards interoperable heterogeneous software programs and operating systems will continue to increase reuse of mainframe technology and provide potentially new applications for mainframe capabilities.
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