Technology review of mainframe computer systems and their alternatives
December 19, 2008 
By Walter F. Tichy, Professor
Faculty of Computer Science
University of Karlsruhe
Karlsruhe, Germany
Mainframe computers, more accurately described as IBM-compatible mainframes, are used by many of the largest companies and government institutions worldwide to store and process critical information. For the purposes of this paper, when we refer to a mainframe, we are describing a computer system capable of running IBM’s proprietary mainframe operating system software such as z/OS, z/VSE or TPF. This definition includes not only mainframe systems from IBM such as System z but also “IBM plug-compatible mainframes” from companies such as Amdahl or Hitachi. IBM estimates that almost ninety five percent of Fortune 1000 companies use IBM’s System z mainframe and that more than 80% of corporate data reside on mainframes. Over 200 billion lines of COBOL applications are in use on mainframes, and more are being added continuously. Many of these applications are custom-built and represent a huge investment for mainframe users. The collective value of mainframe applications written in the COBOL programming language is estimated to be between $1 trillion and $5 trillion, which is worth more than the stock market value of the largest public corporations. Virtually all large businesses and governments have mainframe applications, including vertical applications for the finance sector, public sector, healthcare or manufacturing. IBM claims that “without the IBM mainframe, the global financial system would collapse.” Mainframes are often involved behind the scenes with everyday tasks such as completing ATM transactions or making airline ticket reservations. In addition, mainframes are used to store sensitive consumer, corporate and government information such as health records, financial information and government data. The superior reliability and security characteristics of mainframes drove much of the early adoption of these system for some of the world's most critical IT functions.
After the producers of plug-compatible mainframes exited the market in the late 1990s, IBM became the only supplier of mainframes – a situation that still exists today. Linux, UNIX and Windows systems are lower-cost alternatives that could run mainframe applications. However, IBM refuses to license the intellectual property to make this feasible. In addition, IBM has discontinued licensing its operating system to competitors, stifles interoperability between LUW computers and mainframes, and prevents virtualization solutions that span IBM and non-IBM systems.
As a result of IBM’s actions, there are no longer any competitors in the mainframe market and customers have few viable options for migrating mainframe applications to other more cost-effective platforms. Consequently, customers have been denied the benefits of technological innovation and must instead pay above-market prices for IBM mainframe solutions and premium wages for a dwindling mainframe workforce.
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