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## 7.5 z/OS migration considerations 

Except for base processor support, z/OS releases do not require any of the functions that are introduced with the z15. Minimal toleration support that is needed depends on z/OS release. 

Although z15 servers do not  require any “functional” software, it is recommended to install all z15 service before upgrading to the new server. The support matrix for z/OS releases and the Z servers that support them are listed in Table 7-16. 

<img src='content_image/1009642.jpg'>

a. Server was withdrawn from marketing. 

b. The IBM Software Support Services provides the ability for customers to purchase extended defect support service for z/OS. 

## 7.5.1 General guidelines 

c. See the following z/OS preview announcement: https://www.ibm.com/downloads/cas/US-ENUS219-013-CA/name/ENUS219-013.PDF 

The IBM z15™ introduces the latest IBM Z technology. Although support is provided by z/OS starting with z/OS 2.1, the capabilities and use of z15 depends on the z/OS release. Also, web deliverables$^{12}$ are needed for some functions on some releases. In general, consider the following guidelines: 

GLYPH<SM590000> Do not change software releases and hardware at the same time. 

GLYPH<SM590000> Keep members of the sysplex at the same software level, except during brief migration periods. 

GLYPH<SM590000> Migrate to an STP-only network before introducing a z15 into a sysplex. 

GLYPH<SM590000> Review any restrictions and migration considerations before creating an upgrade plan. 

GLYPH<SM590000> Acknowledge that some hardware features cannot be ordered or carried forward for an upgrade from an earlier server to z15 and plan accordingly. 

GLYPH<SM590000> Determine the changes in IOCP, HCD, and HCM to support defining z15 configuration and the new features and functions it introduces. 

GLYPH<SM590000> Ensure that none of the new z/Architecture Machine Instructions (mnemonics) that were introduced with z15 are colliding with the names of Assembler macro instructions you use$^{13}$. 

GLYPH<SM590000> Check the use of MACHMIG  statements in LOADxx  PARMLIB commands. 

