## 1.1 Introduction 

The decision to migrate from JES3 to JES2 can be difficult because of the following factors: 

GLYPH<SM590000> The current staff lacks JES2 skills. 

GLYPH<SM590000> The cost of migration exceeds the reduction in license fee. 

GLYPH<SM590000> High dependency on JES3 features that you cannot give up. 

GLYPH<SM590000> Your organization sees few benefits in a JES2 migration. 

Additionally, some customers face the following questions: 

GLYPH<SM590000> Is JES3 going away? 

IBM announced the JES3 withdraw after the release following the z/OS 2.4 release. IBM remains committed to help the JES3 clients successfully migrate to JES2 and continues to be available to field questions and help clients plan for a successful migration. 

GLYPH<SM590000> Will JES3 feature new functions? 

Unlikely. However, required changes to maintain the current functionality of JES3 will be done. However, functions are being delivered with JES2, such as the Spool encryption and compression, JES2 policies, Disk Reader capability, and enhancements on JES3 JECL support on JES2. 

GLYPH<SM590000> Do I need to (or should I) migrate from JES3 to JES2? 

The migration should be a business decision that is based on the functions that your organization uses. Migration to JES2 is not currently required. However, remember that the z/OS release after z/OS 2.4 will be the last z/OS release that will include JES3. 

GLYPH<SM590000> If I am new to z/OS, which JES should I use? 

Customers are highly encouraged to use JES2 because JES3 will not be available in the near future. 

## 1.2 Job Entry Subsystem 

GLYPH<SM590000> I was considering migrating from JES2 to JES3. Should I? 

IBM recommends that you avoid migrating from JES2 to JES3. 

Job Entry Subsystem (JES) is a required and strategic part of the z/OS operating system. Up to the z/OS release after z/OS 2.4, IBM offers two JES choices: JES2 and JES3. In the past, JES3 was considered to be the premium choice and continues to have license fees today. 

In the early days of JES2 and JES3, the differences between the two were more obvious than they are today. JES3 was originally developed to assist installations that needed to manage multiple IBM MVS™ images. However, JES2 is used by most z/OS customers and became nearly a superset of JES3 functionality. 

Today, JES3 functions, such as multi-system consoles, automatic tape sharing, dynamic initiators, and workload balancing, can be provided by the operating system. Therefore, they are available to installations that run JES2. This difference has left some JES3 installations wondering whether the premium they pay in licensing fees to run JES3 is still worthwhile. 

Also, with the challenges for the use of integrated technologies and digital transformation, JES2 and JES3 must provide functionality, such as high availability, fault toleration, or digital integration capabilities with new environments. 

