A mainframe has a large number of CPUs. The CPUs can be configured in different modes, called specialty engines.
In this post I will discuss what these specialty engines are, and how they are used.
This post appears as part of a number of articles in the category “Don’t Be Afraid Of The Mainframe”.
General purpose CPUs versus specialty engines
The normal setup to use a CPU is as a general purpose CPU, and alternatively CPUs can be configured as so called specialty engines. This is a special sort of setup that only an IBM engineer can do because the CPU configuration is agreed when you acquire mainframe hardware. We will see why this is.
A general-purpose CPU can be used for, well, everything. But to make it easy, in reality a general-purpose CPU is used only for traditional workload types, like your COBOL and PL/I programs.
When a CPU is configured as a specialty engine, the CPU can only be used for a special function. So a specialty engine is not special in the sense that it is designed for a particular function. Rather, it is a regular CPU that is configured so that it can be used only for a particular function.
The purpose of specialty engines is to make it cheaper for organizations to run particular functions on the mainframe. For traditional workloads the run on the general-purpose CPUs you pay your normal software bill based on MSUs, as we have seen in section Understanding the cost of software on z/OS, MLC and OTC. Functions that run on a specialty engine, however, are not accounted for in the MSU numbers. Therefore, it is up to your software vendor therefore decides whether to enable software to run on a specialty engine. IBM has enabled certain functions for speciality engines, and other vendors have done so similarly for selected mainframe software components.
What is also important to realize, is that even though the general purpose and the specialty engines are using exactly the same hardware, the acquisition cost of a specialty engine is significantly lower than the price for a general-purpose CPU.
Types of specialty engines
The most important types of specialty engines are called zIIP and IFL. I will spare you what the abbreviates mean – they are never used.
A zIIP is a specialty engine that is only usable in a z/OS environment. The special functions you can run on a zIIP are: all Java programs, certain Db2 functions, and z/OS Containers (more on that in separate posts). There are a number of other mainframe software vendors that also enable their software for zIIPs, and they have special conditions for these software products.
An IFL is a specialty engine used to Linux on the mainframe. IFLs have nothing to do with z/OS. The CPUs configured as IFLs can only be used for Linux applications in LPARs running Linux. I will discuss Linux on the mainframe in a separate section Linux for the mainframe.
ICF and SAP
The other types of specialty engines enable the use of the pool of processors in a mainframe for computing needed to support “real” business workloads. These run “technical processing” tasks. The CPU usage is therefore also not accounted for in the software bill. These processor types are the following:
The Integrated Coupling Facility (ICF) processor is used with a Coupling Facility. A coupling facility is a special LPAR that provides special operating system functions in a sysplex. We will discuss the Coupling Facility concepts briefly in section Special sysplex components: the Coupling Facility.
The System Assistance Processor (SAP) specialty engine is used to run I/O operations independently from your central CPUs, in a mainframe component called the IO Subsystem. This type of processors is used when moving data from memory to storage. This not only makes sure that this processing does not add to your software bill, but the IO Subsystem construct also gives the mainframe its extremely fast, high-volume IO processing capability.