Linux vs. z/OS for Mainframe: What’s The Difference?

It wasn’t long ago that Big Iron mainframes were thought to be going the way of dinosaurs. After all, shouldn’t the advent of cloud computing herald the end for those bulky behemoths stored in the basement? The reality is that mainframes provide many of the same benefits that the cloud does, often with more control and security.

Obviously, mainframes have a much higher initial investment requirement than cloud technology. However, many companies have already made that initial investment and are looking to capitalize on the hardware they have. Furthermore, there are companies that continue to invest in their mainframe infrastructure or who plan to in the near future.

It’s quite clear that mainframes (and MIPS) won’t be going extinct in the near future, which is good news for many companies such as IBM.

The Mainframe Mammoth

International Business Machine Corporation, better known as simply IBM, is practically synonymous with mainframes today. IBM has produced various products throughout its long life as a provider of technological solutions for large enterprises.

They began life as the Computing, Tabulating & Recording Company (C-T-R) when they were founded by Herman Hollerith in the late 1800s. During the early years of what was to become IBM, they mostly created punch card readers used for tabulating information like the 1890 US census. It wasn’t until the 1960’s that IBM came out with their first mainframe computer, which has been a flagship product of IBM ever since.

While IBM is practically the de facto manufacturer of mainframe hardware (popularly called Big Iron), the operating systems (OS) running on their machines isn’t necessarily their own. IBM announced plans for the support of the Linux OS on their mainframe hardware at the turn of the 21st century and has continued to dedicate resources towards the popular open source platform.

IBM also continues to update and support their own proprietary OS known today as z/OS. One of IBM’s primary focuses with z/OS is to support backward compatibility with old hardware and software versions to ensure all that Big Iron that has already been bought and paid for remains relevant for as long as possible.

This means IBM actively supports and endorses both Linux and z/OS for mainframes. Arguments can be made for the benefits of z/OS vs. Linux systems relative to one another, but is one truly better than the other? In short: no. There isn’t a clear-cut answer for which is always better; however, there are aspects in which one has the edge over the other. Some of the primary factors to consider for deciding which is best for your organization’s goals are efficiency, compatibility, and staffing.

Efficiency of Linux vs. z/OS

Linux wasn’t originally designed as a mainframe OS. This means Linux is typically run on mainframes in virtual environments through the use of z/VM. Due to the nature of virtual environments, mainframes running Linux will see less than optimal usage of computing power resources.

IBM’s z/OS was designed from the ground up over the course of many decades. Linux, on the other hand, began in the early ’90s as a personal project and didn’t see use on mainframes until the 2000s. If your enterprise needs every ounce of power out of the machines and requires the utmost in reliability, z/OS has the edge.

However, it’s unlikely that every application you run on the mainframe has stringent requirements. If this is the case, you can always run the more resource-intensive processes on z/OS natively and then run your less strict applications on Linux via z/VM virtualization.

Compatibility of Linux vs. z/OS

When it comes to compatibility, Linux tends to win out in terms of support for next-gen applications. Conversely, as was mentioned above, z/OS is developed by IBM specifically to provide backward compatibility with older mainframe applications and hardware. If you are using older technology and expect the need for continued support on those systems, z/OS is the better option.

Linux is essentially a server OS and is supported on a wide range of platforms. This makes for easier porting of Linux workloads to other platforms in the future compared to z/OS which can be costly and cumbersome to port. Having said that, porting Linux workloads off of the z mainframe will see a reduction in the quality of service delivered by the reliability, availability, and performance of running Linux on z/VM on the mainframe. It’s difficult to say which option is best without knowing the specific circumstances of the enterprise using the services.

Staffing for Linux vs. z/OS

Speaking of problems specific to each enterprise, let’s talk about the difficulty of finding skilled professionals. One of the primary benefits offered by Linux is the fact that so many budding developers can easily get their hands on the platform. Thanks to the fact that Linux runs on just about everything, it’s easy for educators to teach Linux and for the self-taught to get first-hand experience.

The same cannot be said about z/OS. Mainframe specific development experience can be hard to come by. However, if your organization has plenty of mainframe vets with years of experience working in z/OS, then problem solved — at least until they retire. Therein lies one of the greatest downfalls of the current z/OS platform: availability for training purposes.

IBM provides the ability to take advantage of both Linux and z/OS through the virtualization of z/VM. The decisions between one or the other must be made on a case-by-case basis and the answer may change over time. The pros and cons of Linux vs z/OS aren’t black and white and can only be weighed when taking into consideration the specific needs of the enterprise looking to implement mainframe technology. This means you need an expert in the field that understands your situation and the technology at hand.