The z/OS zEDC capability is a software-priced feature that is designed to support  compression capable hardware. With z15, the zEDC Express (hardware) PCIe feature is  replaced by the on-chip compression accelerator unit, but the software (z/OS) component is  required to maintain same functionality without increasing CPU costs. All data interchange with existing (zEDC) compressed data remains compatible as z15 and  zEDC capable machines coexist (accessing same data). Data that is compressed and written  with zEDC will be read and decompressed by z15 well into the future.  The on-chip compression unit has the following operating modes: Functionality support for the IBM Integrated Accelerator for zEDC is listed in Table 7-3 on  page 260 and Table 7-4 on page 262. For more information, see Appendix C, “IBM Integrated Accelerator for zEnterprise Data  Compression” on page 503. In this section, we describe the coupling and cluster features.  Coupling facility (CF) connectivity to a z15 is supported on the z14, z13, z13s, or another z15.  The CFCC levels that are supported on Z servers are listed in Table 7-15. Consideration:  Because coupling link connectivity with z14 does not support InfiniBand,  introducing z15 into an installation requires extra planning. Consider the level of CFCC. For  more information, see “Migration considerations” on page 200. Table 7-15 IBM Z CFCC code-levels GLYPH<SM590000> Synchronous execution in Problem State, where user application starts instruction in its  virtual address space, which provides low latency and high-bandwidth  compression/decompression operations). This mod does not require any special  hypervisor support, which removes the virtualization layer (sharing the zEDC Express  PCIe adapter among LPARs requires virtualization support). GLYPH<SM590000> Asynchronous optimization for Large Operations under z/OS. The authorized application  (for example, BSAM/QSAM) issues I/O for asynchronous execution and SAP (PU) starts  instruction (synchronously as described in the previous paragraph) on behalf of  application. The on-chip accelerator enables load balancing of high compression loads  and low latency and high bandwidth compared to zEDC Express, while maintaining  current user experience on compression. 7.4.3 Coupling and clustering features and functions Coupling facility and CFCC considerations 288  IBM z15 (8561) Technical Guide IBM Z server Code level z15 CFCC Level 24 z14 M0x and z14 ZR1 CFCC Level 22 or CFCC Level 23 z13 CFCC Level 20 or CFCC Level 21 z13s CFCC Level 21