Correct sizing of the TLB is subject to complex statistical modeling to find the optimal tradeoff  between size and performance. Main storage is addressable by programs, and storage that is not directly addressable by  programs. Non-addressable storage includes the hardware system area (HSA).  Main storage provides the following functions: Main storage can be accessed by all processors, but cannot be shared between LPARs. Any  system image (LPAR) must include a defined main storage size. This defined main storage is  allocated exclusively to the LPAR during partition activation. The HSA is a non-addressable storage area that contains system LIC and  configuration-dependent control blocks. On z14 servers, the HSA has a fixed size of  192 GB and is not part of the purchased memory that you order and install. The fixed size of the HSA eliminates planning for future expansion of the HSA because the  hardware configuration definition (HCD)/input/output configuration program (IOCP) always  reserves space for the following items: The HSA has sufficient reserved space to allow for dynamic I/O reconfiguration changes to  the maximum capability of the processor. IBM Virtual Flash Memory (VFM, FC 0604) is the replacement for the Flash Express features  that were available on the IBM zEC12 and IBM z13. No application changes are required to  change from IBM Flash Express to VFM. 124  IBM z14 (3906) Technical Guide 3.6.4 Virtual Flash Memory 3.6.3 Hardware system area 3.6.2 Main storage GLYPH<SM590000> Data storage and retrieval for PUs and I/O GLYPH<SM590000> Communication with PUs and I/O GLYPH<SM590000> Communication with and control of optional expanded storage GLYPH<SM590000> Error checking and correction GLYPH<SM590000> Six channel subsystems (CSSs) GLYPH<SM590000> A total of 15 LPARs in the 5 CSSs and 10 LPARs for the sixth CSS for a total of 85 LPARs GLYPH<SM590000> Subchannel set 0 with 63.75-K devices in each CSS GLYPH<SM590000> Subchannel set 1 with 64-K devices in each CSS GLYPH<SM590000> Subchannel set 2 with 64-K devices in each CSS GLYPH<SM590000> Subchannel set 3 with 64-K devices in each CSS