① Explainer · Licensing concepts
The zIIP, zAAP and IFL are processors dedicated to specific workloads on IBM Z. Their licensing power is simple: work they execute does not count toward the general purpose MSU that drives Monthly License Charge software bills. Here is what each engine offloads, how the consolidation of zAAP into zIIP changed the picture, and a worked MSU example.
Processors that work off the meter.
A specialty engine is a processor on an IBM Z machine dedicated to a defined class of work rather than to general z/OS workload. The zIIP, or Integrated Information Processor, offloads eligible work including portions of Db2 for z/OS, Java, XML System Services, and selected system tasks. The zAAP, or Application Assist Processor, was the original engine for Java and XML; IBM folded its function into the zIIP starting with the z13, a setup commonly called zAAP on zIIP, so current estates plan around zIIP capacity. The IFL, or Integrated Facility for Linux, runs Linux and z/VM and underpins the LinuxONE platform.
What ties the three together for a buyer is the meter. Monthly License Charge software is billed on the Rolling 4-Hour Average MSU consumed on general purpose processors. Work that runs on a zIIP, zAAP or IFL does not add to that general purpose peak, and the engines do not raise the MSU rating of the machine. So eligible work moved onto a specialty engine lowers the billable number while the total work done is unchanged. This explainer pairs with our MSU optimization service, where finding unoffloaded eligible work is a standard first pass.
What each specialty engine runs and why it matters to the bill
| Engine | Runs | Status today | Licensing effect |
|---|---|---|---|
| zIIP | Eligible Db2 work, Java, XML System Services, selected system and ISV tasks | Current; absorbed zAAP function | Offloaded work does not count toward general purpose MSU |
| zAAP | Java and XML processing | Consolidated into zIIP from z13 onward | Same MSU exclusion; now delivered via zIIP |
| IFL | Linux and z/VM workloads | Current; the basis of LinuxONE | Outside MLC MSU; Linux work licensed per IFL core |
| General purpose CP | z/OS production workload | Current | This is the MSU that MLC software bills against |
Same workload, a smaller peak.
Take a production LPAR whose Rolling 4-Hour Average peak is 600 MSU, all landing on general purpose processors. Analysis of the SMF data shows that 120 MSU of that peak is zIIP eligible Db2 and Java work that is currently running on general purpose engines because zIIP capacity is constrained. Add zIIP headroom and redirect that eligible work, and the general purpose peak that drives the MLC bill falls to 480 MSU. The total work is identical; only the engine it lands on has changed, and only the general purpose portion is billable MSU.
The figures are illustrative, but the mechanism is exact: only general purpose MSU is billable under MLC, so moving eligible work to a zIIP removes it from the peak. The engine carries a hardware and support cost, which is why the right question is how much eligible work is currently unoffloaded and whether the MSU saved across the term outweighs the engine.
The SMF data shows zIIP eligible work that is still running on general purpose processors, usually because zIIP capacity is short. That gap is billable MSU you could remove. Quantify it before you size anything.
Eligible but unoffloaded is money on the meter.
If eligible work spills onto general purpose engines because zIIP is saturated, adding zIIP capacity pays for itself when the MLC MSU removed across the term outweighs the engine cost. Model both sides.
A saturated zIIP is a tax on the wrong meter.
Many ISV products are written to exploit zIIP. Where a competing product offloads more work to specialty engines, that difference is a real licensing lever at renewal, not just a technical footnote.
zIIP exploitation is a procurement criterion.
Workloads suited to Linux belong on IFL, outside the MLC MSU entirely. Consolidating distributed Linux onto IFL or LinuxONE moves whole workloads off the general purpose meter.
Linux work on IFL never touches the MSU bill.
Specialty processors on IBM Z dedicated to specific work. zIIP offloads eligible Db2, Java and XML and system tasks; zAAP was the original Java and XML engine; IFL runs Linux and z/VM. Work they run does not count toward general purpose MSU.
Not as a separate engine on current machines. IBM folded zAAP function into the zIIP, the zAAP on zIIP arrangement, from the z13 onward. Java and XML work now runs on zIIP, though the term still appears in older contracts.
MLC software bills on general purpose R4HA MSU. Work on a zIIP, zAAP or IFL does not add to that peak, and the engines do not raise the machine MSU rating. Moving eligible work to them lowers the billable peak with the same work done.
IBM and ISVs set eligibility. Common cases are parts of Db2 query and utilities, Java under the z/OS JVM, XML System Services, certain communications and encryption tasks, and ISV products built to exploit zIIP. Measure your own eligible but unoffloaded work first.
Related: licensing concepts hub · sub-capacity vs full capacity · software pricing on LinuxONE · IBM licensing hub · MSU optimization
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