Common Misconceptions About zIIPs

Regular readers of my posts here know that zIIPs are a type of mainframe specialty processor that augments the general-purpose CPUs. Instead of running all workloads on the general-purpose CPUs, specific workloads are shuttled to the specialty processors for execution.

The zIIP, or Integrated Information Processor, was initially created to process certain types of Db2 workloads, but over time the work that can be processed on the zIIP has expanded. Nevertheless, the primary reason for using a zIIP is to reduce costs. You see, IBM does not currently impose monthly software charges on workloads that run on the zIIP.

When you install and start using zIIPs, some percentage of the relevant workload can be redirected from the general processors onto the zIIP specialty processor. But take note; only some things can run on the zIIP. Only workloads IBM deems zIIP-eligible are permitted to run on the zIIP.

Generally speaking, this is newer workloads, that is, things that will encourage more work to run on the mainframe. That is why you won’t see CICS transactions or batch workload as zIIP-eligible, other than for specific work components that match up with zIIP-eligible features defined by IBM.

Common Misconceptions

And that brings us to the main topic of today’s post. There are several common misconceptions about IBM Z zIIP processors. Let’s examine some of them and dispel the misconceptions.

zIIP Processors are Only Useful for Db2

One of the most common misconceptions about zIIP processors is that they are only useful for offloading Db2 workloads. In reality, zIIP processors can offload a wide range of workloads, including Java processing, XML parsing, and encryption/decryption. Another interesting new capability of IBM Z that is zIIP-eligible is the System Recovery Boost. This enables you to take advantage of all of your processing power when starting or restarting your system. This type of boost enables quicker restart and diminishes downtime.

zIIP Processors are Expensive

Another misconception is that zIIP processors are expensive to purchase and operate. While zIIP processors require a separate license, they are generally less costly than general-purpose processors. Their use can result in cost savings by offloading workloads from more expensive processors.

The cost of a zIIP license can vary depending on the specific terms of the license agreement and the number of zIIP processors being used. IBM typically charges a one-time fee for each zIIP processor license and an annual maintenance fee. The cost of the license and maintenance fees can vary depending on the specific terms of the agreement, the number of zIIP processors being used, and other factors.

As another consideration, using zIIPs can help you to forestall costly system upgrades. Suppose workload can be processed on cheaper zIIPs. In that case, your general purpose processors can be utilized for the additional workload that might not have been possible to support if the workload running on the zIIPs had to still run on the general purpose processors. And that means you might be able to run your existing hardware longer, thereby putting off the cost of an upgrade.

zIIP Processors are Less Powerful than General-Purpose Processors

Some people believe that zIIP processors are less powerful than general-purpose processors. There is nothing special about a zIIP processor that makes it different than a general-purpose processor. It is the same hardware. The difference is that only specific workloads are supported. So zIIPs are just as powerful as general-purpose processors when offloading those workloads.

That said, your zIIPs may actually be more powerful than your general-purpose processors. Depending on the type and model of mainframe system you are running, your general-purpose CPU may be knee-capped, meaning it does not run at the full speed it can run. However, zIIPs are never knee-capped, so for a knee-capped system, the zIIP processor will be more powerful than the general-purpose processor.

zIIP Processors are Difficult to Manage

Another misconception is that zIIP processors are difficult to manage. In reality, zIIP processors can be managed using the same tools and processes as general-purpose processors, and IBM provides tools to help administrators monitor and optimize zIIP usage.

zIIP Processors are Only for Large Organizations

Some believe that zIIP processors are only useful for large organizations with complex workloads. However, zIIP processors can be useful for organizations of all sizes and can help reduce costs and improve performance for a wide range of workloads.

zIIPs Cannot Help with COBOL Workloads

Generally speaking, a basic COBOL program will not likely be able to benefit from zIIPs. But, yes, zIIP processors can be used to offload some portion of your COBOL workloads. And not just COBOL, but any workload that meets the zIIP-eligibility criteria can be run on zIIP processors.

Some of your COBOL workloads can be offloaded to zIIP processors if it meets the zIIP-eligibility criteria. For example, if a COBOL application is accessing a Db2 database, some portion of the workload related to database access can be offloaded to zIIP processors. One such example is SQL that is run as a parallel query. This can be offloaded to the zIIP.

Assuming Everything Will Run on the zIIP

Another misconception is the assumption that everything eligible to run on the zIIP will actually run on the zIIP. Although this may seem like a reasonable assumption, not everything that is zIIP-eligible will actually run on the zIIP.

Some percentage of the relevant workload will be redirected off the main CP onto the zIIP – but not 100% of the workload. When an enclave is created by a product you are using, a parameter can be set to impact the CPU percentage that z/OS can make eligible to run on the zIIP.

Take a look at the Db2 13 for z/OS documentation and you will see that not all zIIP-eligible workloads are 100% eligible. For example, the DRDA workloads using TCP/IP and native REST calls over HTTP are up to 60% off loadable to the zIIP.

Furthermore, if the zIIPs are stressed, based on your configuration choices, it is possible that zIIP-eligible workload can run on the main CPs. So, not everything that is zIIP-eligible will actually run on your zIIPs. But enough to likely make them cost-effective.


Overall, zIIP processors are a powerful and cost-effective tool for offloading specific workloads on IBM Z mainframes. While some common misconceptions exist about zIIP processors, understanding their capabilities and limitations can help organizations make informed decisions about their use.


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