7.5 z/OS migration considerations 7.5.1 General guidelines 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. a. Server was withdrawn from marketing.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. 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. Table 7-16 z/OS support summary z/OS  Release z10 EC z10 BC WDFM a z196  z114 WDFM a zEC12 zBC12 WDFM a z13  z13s WDFM a z14 z15 End of Service Extended Defect Support b V2R1 X X X X X X b 09/2018 09/2021 V2R2 X X X X X X 09/2020 b 09/2023 b V2R3 X X X X 09/2022 b 09/2025 b V2R4 c X X X - - 12 For example, the use of Crypto Express7S requires the Cryptographic Support for z/OS V2R1 - z/OS V2R3 web  deliverable. 13 For more information, see the Tool to Compare IBM z15 Instruction Mnemonics with Macro Libraries IBM  Technote. Chapter 7. Operating system support  321