In my previous post, I mentioned that we need to understand the distinction between model number and capacity setting.  We’ll take a look at that now, but it may help if I first explain a few things.

1. What is a PU?  It stands for processor unit (because that’s what it is – a processor).  We sometimes call it an “engine.”  It’s basically analogous to a “core,” for those of you from a PC background.  On a mainframe, it’s called a PU.

2. The PUs of which I’m going to speak are engines that are (potentially) configurable by the customer.  In other words, the PUs are processors that are available to the customer for use in running their workload.

Now, here’s the deal.

If I order a z10 model Enn, that z10 has nn PUs physically present.  For example, if I order a 2098 E10, there are 10 PUs available in the machine.  Do I get to use all ten for my workload?  Only if I purchased ten.   If I purchased only four PUs, then I can use those four and I have six inactive PUs left over.

Let’s revisit something from the previous post and look at the real numbers.

We identified the following z10 models:

The z10 BC has one model: the E10.

The z10 EC has five models: the E12, E26, E40, E56, and E64.

So, from this you see that a z10 BC (machine type 2098, model E10) has ten PUs available.

The larger z10 EC (machine type 2097) has the following models:

2097-E12 with twelve PUs.

2097-E26 with twenty-six PUs.

2097-E40 with forty PUs.

2097-E56 with 56 PUs.

2097-E64 with 64 PUs.

How does knowing this help me?

Okay, that’s a fair question.  Let’s consider an example.  Suppose I have a z10 EC 2097-E12 and I’m running it as a ten-way server.  If I need to scale it up to an eleven-way or a twelve-way server, to meet my growing workload, I can do so by turning on one or two additional engines.   The engines are there, physically present – I just need to pay for them and have them activated.   This can be done via a microcode update without having to bring the machine down.  If I need to turn on more than two engines, then I will need to move to the next model, the E26.  That’s not complicated, but it involves a little more time and expense than just activating some dormant PUs with a microcode change.

So now where are we?

Well, we’ve discussed z10 classes, machine types, and model numbers.  We’ve also shown that the model number tells you the number of PUs present in the machine.  Here’s a recap:

z10 BC is the Business Class offering.

It’s sized for entry-level up to mid-sized businesses.

It has machine type 2098 and one model, the E10.

z10 EC is the Enterprise Class offering.

It’s sized for mid-sized to high-end businesses.

It has machine type 2097 and models: E12, E26, E40, E56, and E64

Why do I call this the model mystery?  Because I suspect that most mainframe users cannot tell you the model of their machine.  But they can tell you their capacity setting.  We’ll cover that in the next post.