DBAOTM Operating systems for the big mainframe box

In the previous posts I have given an overview of the most important mainframe hardware components. In this article I will summarize what operating systems you can run on this hardware. But first…

This post appears as part of a number of articles in the category “Don’t Be Afraid Of The Mainframe”.

What is actually a mainframe

A little late to answer this question, but I thought it was good to address this here.

A mainframe is a large computer that is designed to run many different computing tasks at the same time. A mainframe stems from the time where hardware was expensive, and a single central solution for computing was the only way to economically run computing tasks.

A lot of characteristics of that design point are still prevalent today. Hence it is good to understand this background.

z/OS and Linux, and then some…

A number of operating systems can run on the mainframe. I will give a short description here of the operating systems you can run on a mainframe.

For the rest of the series of articles I will focus on the two most important ones today. z/OS is the most important mainframe operating system, but also the most different from today’s mainstream operating systems. I will discuss z/OS most extensively.  Linux for the mainframe is the second most important operating system and has gained popularity over the past decade. I will discuss Linux for the mainframe in a separate chapter Linux for the mainframe.


IBM often calls z/OS their flagship mainframe operating system. The roots of z/OS date back to 1964, when the operating system OS/360 was designed for the System/360 computer, the predecessor of IBM’s modern mainframe computers. In the early 70s the successor of the OS/360 operating system was developed, and named MVS (it stands for Multiple Virtual Storage, but you can forget that immediately). MVS has evolved further into OS/390 and now it is called z/OS. The name changes may suggest fundamental different systems, but these are in fact only marketing-driven name changes for MVS and the technology base is still the same, although it has very significantly evolved.

z/VM, the mother of all hypervisors

z/VM, or VM (VM stands for Virtual Machine) as it was originally named, used to be a full-fledged operating system that was design to run business applications. The operating system included a unique technology that allowed users to virtualize the mainframe hardware and split it up into small virtual machines. Nowadays we have VMWare, KVM, Xen, Hyper-V and others that do the same for x86 and other platforms. But the technology in VM was developed in the 1960s. It was far ahead of it’s time. z/VM can be considered the mother of all hypervisors.

z/VM is nowadays it is only still used as a hypervisor for the mainframe, and is no longer as an operating system for business applications.


The z/VSE operating system is the small brother of z/OS. It was developed in parallel to MVS, and targeted smaller customers. Nowadays it is not used very much anymore, but it is still developed and supported by IBM.


The operating system z/TPF (Transaction Processing Facility) was developed especially for real-time computing. Organizations that needed to process large volumes of small transactions very fast, such as credit card companies, airline and hotel reservation systems, and banks have deployed this specialized mainframe operating system.


IBM has ported Linux to the IBM mainframe architecture and the first release was formally announced in the year 2000. Since that time many other software products, commercial as well as open source software, have been made available on Linux for Z, as it is now called.

Configuration for Linux for the mainframe are most often virtualized with z/VM, the hypervisor for the mainframe we saw above. With z/VM you can create and manage many virtual machines on the mainframe in which you can then run a Linux instance. I will discuss Linux for the mainframe separately in a number of special posts.