3.2 ISM that uses SMC-D 3.2.1 HiperSockets, SMC-R, and SMC-D The IBM z13 GA2 and IBM z13s™ introduces an Internal Shared Memory (ISM) virtual PCI  function. ISM is a virtual PCI network adapter that enables direct access to shared virtual  memory, which provides a highly-optimized network interconnect for z Systems intra-CPC  communications.  When ISM is used by z/OS Version 2.2 by using Shared Memory Communications - Direct  Memory Access (SMC-D), the combined solution provides improved transaction rates for  interactive (request and response) workloads. This improvement is due to reduced network  latency and lower CPU cost for workloads with larger payloads, such as analytics, streaming,  big data, or web services. The combined solution also preserves the key qualities of services  that are required by z System clusters in enterprise data center networks. Customers who have multiple z/OS instances on a single CPC with z/OS centric workloads  that use TCP communications, such as Db2, IBM WebSpherefi Application Server, IBM  CICSfi, IBM MQ, and IMS among them are the primary beneficiaries of this new support. The target audience of this IBM Redbooks publication are mainly users who work in the Db2  for z/OS area. For the benefit of those users that are not deeply involved in the  communication server and hardware aspects, we provide some background in this section to  where SMC-D fits into the larger picture. Co-location of multiple tiers of a workload onto a single z Systems platform allows for the use  of IBM z Systems internal communications. IBM z Systems HiperSockets™ is an internal  LAN technology that provides low-latency connectivity between virtual machines within a  physical z Systems central processing complex (CPC). HiperSockets is logically represented to the host as a standard network interface controller  (NIC) with access to an IEEE standard LAN. It is implemented fully within z Systems  firmware, so it requires no physical cabling or external network connection to purchase,  maintain, or replace. The performance benefits of HiperSockets when compared to the use of an external LAN  connection over Open Systems Adapter-Express (OSA-Express) are achieved in large part  because the physical layer (Ethernet) processing is avoided. However, for the plethora of applications that use TCP/IP for network communications, the  communications and packet-processing aspects of the software stack remain. Data is formed  into, transmitted, and received in fully compliant TCP/IP packets. Traditional IP routing is also  used.  All standards that are relevant to TCP/IP processing, such as checksum, segmentation, flow  control, reordering, and retransmission, are used when communicating over HiperSockets.  This processing occurs at the appropriate operating system communication stack software  layers. A significant amount of overhead is also incurred with the associated interrupt  processing, memory management, context switching, and thread dispatching. Chapter 3. Synergy with the IBM Z platform  93 IBM z Systems HiperSockets