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## D.3.2 Internal Shared Memory technology overview 

ISM is a function that is supported by the z14, z13, and z13s systems. It is the firmware that provides the connectivity for shared memory access between multiple operating systems within the same CPC. It provides the same functionality as SMC-R, but without physical adapters (such as the RoCE adapter) by using instead virtual ISM devices as SMC-R. It is a HiperSocket-like function that provides guest-to-guest communications within the same machine. A possible solution that uses only SMC-D is shown in Figure D-10. 

<img src='content_image/999017.jpg'>

SMC-D and SMC-R technologies can be used at the same time on the same CPCs. A fully configured three-tier solution that uses SMC-D and SMC-R is shown in Figure D-11. 

<img src='content_image/999018.jpg'>

## D.3.3 SMC-D over Internal Shared Memory 

ISM is a virtual channel that is similar to IQD for HiperSockets. A virtual adapter is created in each OS. The memory is logically shared by using the SMC protocol. The network is firmware-provided and a new device is required to manage that virtual function. SMC is based on a TCP/IP connection and preserves the entire network infrastructure. 

SMC-D is a protocol that allows TCP socket applications to transparently use ISM. It is a “hybrid” solution, as shown in Figure D-12 on page 440. 

