---
title: "Logical Partition (LPAR) in Mainframe – Real Purpose"
description: "Logical partition s (LPARs) are, in practice, equivalent to separate mainframes. Each LPAR runs its own operating system. This can be any mainframe operating system; there is no need to run z/OS®, for..."
url: https://srinimf.com/2013/02/10/mainframe-lpar-and-prsm/
date: 2013-02-10
modified: 2026-10-10
author: "Srini"
image: https://i0.wp.com/srinimf.com/wp-content/uploads/2013/02/pexels-photo-7092416.jpeg?fit=1880%2C1253&ssl=1
categories: ["Categories"]
tags: ["LPAR", "Mainframe tips", "PR/SM"]
type: post
lang: en
---

# Logical Partition (LPAR) in Mainframe – Real Purpose

[Logical partition](https://srinimf.com/2013/01/02/oracle-lpar/)s (LPARs) are, in practice, equivalent to separate mainframes. Each LPAR runs its own operating system. This can be any mainframe operating system; there is no need to run z/OS®, for example, in each LPAR.

The installation planners may elect to share I/O devices across several LPARs, but this is a local decision.

- [How to Implement Credit Cards Project Using CICS in Mainframe](https://srinimf.com/2016/06/08/card-payments-and-banking-projects-cics-for-zos-mainframe/)

## How it Works

The system administrator can assign one or more system processors for the exclusive use of an LPAR. Alternately, the administrator can allow all processors to be used on some or all LPARs. Here, the system control functions (often known as microcode or firmware) provide a dispatcher to share the processors among the selected LPARs.

- [How to Learn Mainframe Skills Easily](https://srinimf.com/2017/06/18/next-way-to-move-into-hot-digital-career/)

## Who will specify Processors

The administrator can specify a maximum number of concurrent processors executing in each LPAR. The administrator can also provide weightings for different LPARs; for example, specifying that LPAR1 should receive twice as much processor time as LPAR2.

```
LPAR will be created by DEFINE LPAR lparname CSS01 MIF_id 3
```

In mainframe computing a **PR/SM** (**Processor Resource/System Manager**) is a type-1 [Hypervisor](http://en.wikipedia.org/wiki/Hypervisor) (a [virtual machine](http://en.wikipedia.org/wiki/Virtual_machine)) that allows multiple [logical partitions](http://en.wikipedia.org/wiki/LPAR) to share physical resources such as [CPUs](http://en.wikipedia.org/wiki/Central_processing_unit), [I/O channels](http://en.wikipedia.org/wiki/Channel_I/O) and [direct access storage devices](http://en.wikipedia.org/wiki/Direct_access_storage_device) (DASD). It is integrated with all [IBM System z](http://en.wikipedia.org/wiki/IBM_System_z) machines.

- [Mainframe Vs Docker Top Differences](https://srinimf.com/2018/12/08/undesratnd-docker-useful-for-legacy-programmers/)

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