The IBM System z Integrated Information Processor (zIIP) is a specialty engine designed to offload eligible database workload from a GCP (general central processor) to a zIIP.
Offloading workload to a zIIP helps optimize resource capacities and expand the use of a GCP for new workloads, while lowering the mainframe TCO (total cost of ownership). In contrast to the expensive GCP which may even run throttled, the zIIP is inexpensive and always runs at full speed.
For detailed information on the zIIP, refer to the appropriate IBM literature.
The simple graphic below illustrates the purpose of the zIIP: