Types of mainframe computers

Updated March 23, 2017

Mainframes are high-performance computers used for large-scale intensive processing not possible using normal machines. They have traditionally been used by banks, government agencies and corporations requiring a dependable and secure computer for carrying out vital transactions and storing vast amounts of data. Mainframes differ in their operating systems, manufacturers and data code sets.


The first mainframe appeared in 1944 at the Moore school. Known as Eniac, an acronym for electronic numerical integrator and calculator, the computer possessed 30 separate units and weighed over 30 tons. Inside were 1,500 relays, 19,000 vacuum tubes and hundreds of thousands of resistors, inductors and capacitors. In 1951, the UNIVAC I mainframe computer was delivered to the U.S. Census Bureau. The UNIVAC differed from the ENIAC in that it processed each digit serially. The 1950s were the heyday of mainframe computing and saw their extensive manufacture by companies such as IBM, Control Data, NCR, General Electric, UNIVAC, Burroughs, Honeywell and RC. Although the early mainframes marginally differed in how they stored and processed information, they all shared the aim of carrying it out from a central location.

Modern Mainframes

Modern mainframes exist in two forms. The first are the newly built multipurpose machines no longer solely restricted to centralised computing. They are able to serve distributed users and the smaller servers of a computing network. The other type is the old mainframes that have been overhauled to deal with modern requirements, such as running Internet-based programs. Despite predictions that mainframes would be extinct before the turn of the last millennium, these machines are proving to be what Steve Lohr from IBM termed as "the classic survivor technology".

Operating Systems

The majority of modern mainframes are manufactured by IBM, Hitachi and Amdahl. IBM-made machines use the MVS operating system. MVS systems feature a time-sharing option environment similar to the DOS prompt familiar to PC users. This allows users to query the type of mainframe being used and the system's general health. Other mainframes use the Unix, Linux, z/OS, OS/390, VM and VSE operating systems.

Mainframe Data Types

Mainframes store data in one of two ways. Most use the EBCDIC code set, though some may use the ASCII code set. The code set relates to the way mainframes code the alphabet internally. For example, those using the ASCII code set store the letter "A" as the hexadecimal value 45 (65 decimal). In the EBCDIC code set, the same letter is represented by the hex value C1 (193 decimal). Data cannot be transferred between machines using different code sets without first being converted.

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About the Author

Justin Schamotta began writing in 2003. His articles have appeared in "New Internationalist," "Bizarre," "Windsurf Magazine," "Cadogan Travel Guides" and "Juno." He was a deputy editor at Corporate Watch and co-editor of "BULB" magazine. Schamotta has a Bachelor of Science in psychology from Plymouth University and a postgraduate diploma in journalism from Cardiff University.