Virtualization, Hypervisors and Mainframe!

Vikas Pujar
4 min readMay 28, 2022

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Introduction

Mainframe celebrated its 58th birthday on April 7, 2022. Mainframe technology has evolved over six decades and still remains an important part of the ever-changing IT landscape. Mainframe workloads are expected to grow in the coming years, as per the latest survey¹.

Not many know, that the origins of virtualization can be traced back to the 1970s, when it was initially introduced on the mainframe. This blog post will touch base on the virtualization, hypervisor offerings on the mainframe.

Chapter 1 : Virtualization and Hypervisors

Before we get into the details of mainframe virtualization, let’s understand virtualization and hypervisors.

Virtualization is a technology that lets you use a single physical hardware system to create many virtual environments called “Virtual Machines” — VM’s”

Hypervisor is software that creates and runs virtual machines (VMs). Hypervisors are classified as Type 1 or Type 2 based on their architecture.

Type 1 hypervisor

A Type 1 hypervisor runs directly on the underlying computer’s physical hardware, interacting directly with its CPU, memory, and physical storage. For this reason, Type 1 hypervisors are also referred to as bare-metal hypervisors. Note that, a Type 1 hypervisor takes the place of the host operating system. Example (x86}: Microsoft Hyper-V hypervisor, VMware ESX/ESXi etc.

Type 2 hypervisor

A Type 2 hypervisor doesn’t run directly on the underlying hardware. Instead, it runs as an application on an operating system. Note that, a Type 2 hypervisor runs on top of the Host OS. Example (x86): VMware Workstation, Microsoft Virtual PC etc.

Below image depicts Type 1 and 2 hypervisors.

Image 1 — credit: vembu.com

Chapter 2 : Virtualization and Hypervisors on Mainframe

As mentioned, virtualization is not new to the mainframe. In 1972² !!, IBM released VM/370, which was the first commercially available operating system with built-in virtualization capabilities. It was in 1999 that VMware released the virtualization solution for x86 hardware named VMware Workstation³.

On mainframe also, the hypervisor offerings can be categorized as Type 1 (Hardware Based Virtualization) and Type 2 (Software Based Virtualization).

Type 1 Hypervisor : Hardware-based virtualization on the mainframe

Processor Resource/Systems Manager (PR/SM) is a Type 1 hypervisor that operates directly on the mainframe’s bare metal, is at the heart of all virtualization on the z platform. Since it runs directly on top of the z hardware, it is categorized as a Type 1 hypervisor.

On z, you can create up to 85 LPARs⁴ — Logical Partitions. LPARs can be loosely compared to a single physical server. Each LPAR has its own operating system, logical processor and memory capabilities.

Type 2 Hypervisor : Software-based virtualization on the mainframe

z/VM is a Type 2 hypervisor that can operate multiple virtual machines, each with its own operating system. Since z/VM does not run directly on z hardware, it is categorized as a Type 2 hypervisor⁵ *.

With the help of z/VM, a single mainframe can run hundreds of thousands of virtual machines and a diverse set of workloads without being tied to a particular operating system. For example, refer to image 2, where LPAR 3 runs three operating systems. (For more information on the operating systems that run on IBM z, refer to my blog https://vikaspo.medium.com/is-mainframe-available-on-cloud-5bdae6c7d489)

Also note that apart from z/VM there is another software-based virtualization known as KVM. KVM is also a Type 2 hypervisor that provides open-source virtualization capabilities. Red Hat, SUSE and Ubuntu all offer Linux distributions that include a KVM module optimized for the z platform.

Below is an example of hypervisor(s) Type 1 an 2 running on IBM z.

Image 2
  1. The PR/SM runs on top of hardware and in turn manages multiple LPAR’s. In this example, it’s running 5 LPAR’s (recall that z supports up to 85 LPAR’s)
  2. LPAR 1 runs the core mainframe operating system z/OS
  3. LPAR 2 runs the z/TPF operating system
  4. LPAR 3 runs the software-based hypervisor z/VM and in turn, z/VM runs guest operating systems z/VSE and Linux on z
  5. LPAR 4 runs Linux on z
  6. LPAR 5 runs the software-based hypervisor KVM and in turn, KVM runs guest operating systems like Linux on z

*It’s important to note that the lines between z/VM being categorized as type 1 and type 2 hypervisors are blurred; I’ve seen it labeled as Type 1 in some articles, but the reference I have provided lists it as Type 2⁵. z/VM does not fall into the description of a Type 1 hypervisor because it operates on top of Type 1!! Ah, I know it’s a bit puzzling. It would be interesting to hear your thoughts on this subject.

Chapter 3: Conclusion

Virtualization technology has been crucial in the growth of cloud computing, and the fact that it has its roots connected to the mainframe indicates that the mainframe was never conservative. The new z16, released in April 2022, includes features such as AI on Chip and Quantum Safe, making it future-proof and technology to look out for (should I say another 5 decades :-))

As I write this blog, Broadcom has announced the acquisition of VMware, and Broadcom acquired the mainframe focused company Computer Associates a few years ago. As a result, it will be interesting to see what the future holds for the mainframe community in the coming days in terms of virtualization offerings.

References

[1] https://www.bmc.com/info/mainframe-survey.html

[2] https://vicominfinity.com/it-trends/Mainframe-Virtualization.php

[3] https://en.wikipedia.org/wiki/VMware

[4] https://techchannel.com/Trends/02/2020/z15-leap-for-ibm-z

[5] https://www.redbooks.ibm.com/redbooks/pdfs/sg248147.pdf

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Vikas Pujar
Vikas Pujar

Written by Vikas Pujar

Mainframe Modernization and Cloud Architect

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