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Taking a Second Look at “Big Iron”

During our second seminar of the semester, we spent some time discussing mainframes (a.k.a. “big irons”). To be honest, I was quite confused during this part of the seminar and for that reason have decided to use this blog post as an opportunity to research and explain what, in fact, a mainframe actually is.

An IBM 704 mainframe. IBM produced the 700/7000 series of mainframes from the 1950s through the early 1960s.

According to the IBM (i.e. International Business Machines) knowledge center, the term “mainframe” used to refer only to an early physical computer. These early machines used to take up as much space as a room and required their own air conditioning systems. As opposed to supercomputers, which are meant to process large quantities of data and are ideal for things like medical research and weather forecasting, mainframes are designed to process high volumes of simpler transactions. Nowadays, though, “mainframe” can also refer to  “a style of operation, applications, and operating system facilities” (“What is a Mainframe?”). From what I gather, this means that systems that serve similar purposes to the original, huge mainframe computers can also be referred to as mainframes; that is, the same operations that used to require mammoth IBM operating systems can now be executed on smaller devices.

The 2015 IBM z13 mainframe. It was designed specifically with supporting secure transactions over mobile apps in mind. As you can see, they’re still very large–about the size of a refrigerator.

But what are these operations, exactly? Today, mainframes are often used to process high volumes of transactions, especially ones that must be done securely. Mainframes are extremely reliable, as they have many built-in redundancies and are designed to support a lot of I/O (input/output); specifically, the modern IBM mainframe can have upwards of 160 I/O cards. Mainframes are used by most major banks in the United States, retailers, and airline ticketing systems. And you’ve likely used a mainframe yourself, whether or not you knew it! When you withdraw money from an ATM, you use a mainframe to access your bank account. It’s the same if you are checking your account through a web browser like Safari or Google Chrome. Other major uses for mainframes include managing large amounts (e.g. terabytes) of data in databases and supporting thousands of users and apps utilizing certain resources simultaneously (“Who uses mainframes”).

Check out the video from Techquickie below for more details!


Works Consulted

Alba, Davey. “Why on Earth Is IBM Still Making Mainframes?” Wired, Conde Nast, 13 Jan. 2015. <>

“What is a Mainframe? It’s a Style of Computing.” IBM Knowledge Center, IBM, 2010. <>

“Who Uses Mainframes and Why Do They Do It?” IBM Knowledge Center, IBM, 2010. <>



  1. Mike Smith

    I hope that I didn’t confuse you too much in class this past week! Your post demonstrates that you do understand the concept and the terminology. Overall, it’s not easy to define definitively one class of computer from another because all computers are meant to be flexible and different customers want their computing infrastructure to support their business, which is different from customer to customer. The other interesting phenomenon that complicates this classification is that technology moves up and down the categorization. Microprocessors (i.e., single chip implementations of the “brains” of computers) started out at the personal and embedded side of the categorization, but as microprocessor technology improved, these chips ended up powering many mainframes. On the other hand, high-powered floating-point units started out in supercomputers, but eventually made their way into personal computers. Your blog, however, emphasizes the important characteristics of what most call mainframes. Thanks for sharing your investigations!

  2. Jim Waldo

    Thanks for doing some great research, and don’t feel bad about not understanding…I had students in my graduate level course ask me what a mainframe was when I last taught the course.

    Another way to characterize a mainframe is that all of the users of the mainframe share everything– all the files, the processor, the memory and the like. That means that you can keep all the data consistent, since you don’t have different copies of the data on different machines that need to be updated when someone wants to make a change. This consistency is one of the reasons that, say, banks like mainframes– the last thing you want is for the data about money to differ. It’s worth paying the extra money to have a single, really big machine.