Agility
Agility is determined by the features of the applications themselves, the development environment, and the application infrastructure. If you migrate an application to Windows, your programmers can then use the native capabilities of the Microsoft developer tools and applications like Microsoft SQL Server and Microsoft Biztalk Server, enhancing their productivity and reducing time to market for new applications. Agility improves the more these Microsoft products are used in the application.

Supportability
Migration solves issues around the availability of skilled computer professionals. Migration also enables companies to choose between systems from multiple manufacturers on which to run those applications, and from multiple suppliers. Overall supportability improves the more applications are moved off the mainframe.

Cost Savings
Improved productivity results in reduced labor costs for development, and increased system vendor choice improves procurement prices and terms. Also, Windows software and Intel / AMD systems typically sell for significantly less than their mainframe equivalent. Although a migrated application may result in substantial cost savings, the total cost savings are capped until the fixed overhead of the mainframe system is eliminated.

Rehosting consists of recompiling or converting the mainframe applications to run on Windows Server (for example, running a mainframe COBOL/CICS application in the Windows environment).

Porting consists of using language translation tools to develop identical applications on Windows (for example, using a tool to convert mainframe COBOL to C#).

Replacement consists of replacing existing mainframe applications with available Windows software packages (for example, replacing a custom built CRM or ERP application with SAP running on Windows Server or with Microsoft Dynamics).

Rewriting involves viewing the existing mainframe application as the initial functional specification for a new application on Windows, and then writing the application in Windows using native languages and tools.