Specialty Processors on the Mainframe
If you use an IBM z Series mainframe you've undoubtedly heard about zIIPs and zAAPs and other specialty processors. But maybe you haven't yet truly examined what they are, what they do, and why they exist. So, with that in mind, let's take a brief journey into the world of specialty processors.
Over the course of the past decade or so, IBM has introduced several different types of specialty processors. The basic idea of a specialty processor, is that it sits alongside the main CPUs and specific types of "special" workload is shuttled to the specialty processor to be run there, instead of on the primary CPU complex. Why is this useful or interesting to mainframe customers? Well, the specialty processor workload is not subject to IBM or ISV licensing charges...and, as every mainframe shop knows, the cost of software rises as capacity on the mainframe rises. But if capacity can be redirected to a specialty processor, then software license charges do not accrue-at least for that workload.
Another benefit of the specialty processors is that they are significantly cheaper to acquire than standard CPUs. A standard mainframe CP costs a quarter of a million dollars, whereas a specialty processor can costsless than $50,000. That is less than one-fifth the price of the standard processor. But there is a catch. The specialty processors can only run certain types of workloads-at least that is so as configured by IBM "out of the box."
There are four types of specialty processors:
- ICF: Internal Coupling Facility-used for redirecting coupling facility cycles in a data sharing environment
- IFL: Integrated Facility for Linux -used for processing zLinux workload on an IBM mainframe
- zAAP: Application Assist Processor-used for the Java virtual machine
- zIIP: Integrated Information Processor-used for processing certain, distributed database workloads
When you activate any of these processors, some percentage of that type of workload can be redirected off of the main CP onto the specialty processor-but not 100% of the workload. Indeed, one of the frustrating issues, particularly with the zIIP, is that it is difficult to understand exactly what is redirected exactly when and exactly how much of it. In general, distributed DB2 for z/OS workload and XML processing can be redirected to zIIP processors.
Additionally, to run on a zIIP, the workload must run under an enclave SRB. So, code written to execute under a TCB usually will be unable to execute under an SRB without major changes. But the point of this article is not really to explain "how" to redirect work to a specialty processor, but to examine the pros and cons.
So what is the point of specialty processors? In other words, why is IBM doing this? It seems to me that IBM is promoting specialty processors to extend the life of the mainframe platform. I am a big mainframe proponent and have argued that it is not a dying platform. Nevertheless, some organizations have abandoned (or are trying to) the mainframe for more modern workloads: Java, XML, Linux, web development, etc. By offering inexpensive specialty processors for the mainframe that run this type of workload, IBM is hoping to encourage more modern workloads to be built for, and run on, the mainframe.
Longtime mainframers are skeptical, as they should be. The big question many have asked is "Why doesn't IBM just decrease the price of the hardware instead of introducing new processors that only run certain workloads?" And that is the correct question to be asking-at least from the customer perspective. But I believe IBM's goal is not to reduce overall mainframe prices ... why would they when there is almost no competition? Lowering prices would not protect the large revenue stream IBM earns from mainframe hardware and software.
It would seem that the specialty processor approach has the desired effect of keeping mainframe shops running their legacy batch and transaction processing workload on the expensive hardware (because there is little competition), while reducing the price for new workload (because there is stiff competition).
But the bottom line is this: Specialty processors can help to reduce the cost of mainframe computing. And there are software alternatives from ISVs to help organizations more effectively utilize specialty processors for more and varied types of workloads.