---
title: "Mainframe -OS/390 and ZO/s difference"
description: "This question asked for many mainframe programmers. They are unable to tell correct answer. For your benefit I am giving the basic difference. https://srinimf.com/2015/12/18/the-linux-mainframe-emulat..."
url: https://srinimf.com/2015/11/11/mainframe-os390-and-zos-difference/
date: 2015-11-11
modified: 2026-10-10
author: "Srini"
categories: ["Categories"]
tags: ["OS/390 and ZO/s difference"]
type: post
lang: en
---

# Mainframe -OS/390 and ZO/s difference

This question asked for many mainframe programmers. They are unable to tell correct answer. For your benefit I am giving the basic difference.

Related[Mastering VSAM: A Comprehensive Guide](https://srinimf.com/2016/10/20/the-excellent-vsam-free-tutorial-presented-in-simple-way/)

OS/390:

This architecture runs under 32 BIT address space

Z/OS:

This architecture runs under 64-BIT address space.

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