The mainframe has several kinds of engines as processors in addition to the central processor (CP). Today, there are several flavors of processors that perform various functions, but early mainframes had only one—the CPU. As the mainframe industry evolved over the past few decades, mainframes began to have a central processor complex (CPC) consisting of several kinds of processors. Each processor type is used for a specific purpose. Technically, all processors are the same out of the box, and they’re configured as specific engine types during installation. Unlike CPs, which can be configured to run at a lower speed for software cost reasons, specialty processors usually run at full speed.
Specialty processors are typically configured and used for two main reasons: To lower software costs and to process eligible new workloads. To understand how a specialty processor can lower software costs, we need a clear understanding on how software costs are billed on the mainframe. The main point to note in the mainframe software billing world is that workloads running on specialty processors don’t count toward software costs—but workloads running on CPs do. You can still run these workloads on CPs that otherwise could run on specialty processors. But when these workloads run on CPs, they could contribute to your monthly software costs.
Mainframe customers are often charged for software that runs on a mainframe based on peak millions of service units (MSU) usage through a monthly software license charge (MLC). To determine the MLC, the mainframe OS generates monthly reports that determine a customer's system usage (in MSUs) during every hour of the previous month using a rolling average (e.g., a 4-hour rolling average) recorded by each LPAR or a capacity group. The hourly usage metrics are then aggregated together to derive the total monthly and hourly peak utilization, which is used to calculate the monthly bill.
Processor Types and Functions
Central Processor (CP): This is a general-purpose processor used by z/OS and other software applications. Work executed on this processor counts towards a software bill. This processor can run at lower speeds to reduce software costs.
Integrated Facility for Linux (IFL): IFL is used for Linux OSs running on mainframe. Linux can run on CP processors as well, but running Linux over IFL would lowers software costs because workloads on IFL don’t contribute to your bill.
Integrated Coupling Facility (ICF): ICFs are used with a coupling facility, which is a special LPAR that provides functions like caching, locking and listing in a sysplex.
System Assistance Processor (SAP): SAP engines are used with I/O Subsystems, and each system could have several SAPs. SAPs can help with translation of device numbers and channel path identifier, managing multiple paths to control units and more.
IBM zEnterprise Application Assist Processor (zAAP): zAAP processors run eligible Java workloads. If zAAPs are configured, then z/OS will direct eligible Java workloads to run on the zAAP. As mentioned earlier, if you don’t have zAAP engines configured, you could still run these workloads on CPs but that could contribute towards your software bill. The main purpose of a zAAP engine is to offload some of the workloads (e.g., Java code) from CPs to lower software bills. Note that new z13 machines and zIIP specialty engines will also run workloads that are eligible to run on zAAP specialty engines. zAAP engines will no longer be supported beginning with the z13.
IBM z Integrated Information Processor (zIIP): zIIPs are specialty processors that run eligible database workloads. Similar to zAAPs and IFLs, zIIP processors offload specific workloads that otherwise run on CPs, thereby reducing software costs. Beginning with z13, zIIP processors are able to run zAAP eligible workloads.
Hemanth Rama is a senior software engineer at BMC Software. He has over 11 years of experience in IT. He holds two patents and one pending patent application. Hemanth works on BMC Mainview for z/OS, CMF Monitor and Sysprog Services product lines and has also led several projects. He recently began working on Intelligent Capping for zEnterprise (iCap), a product which optimizes MLC costs. Hemanth holds a master’s degree in computer science from Northern Illinois University. He writes regularly on LinkedIn pulse, BMC communities and his personal blog.