As the computer industry knows, the mainframe is “not dead”. That means mainframe software licensing is still alive and people working with mainframes should understand as much as possible about licensing of products on that platform. This is one part of the SAM process for an Enterprise.

A comment I frequently hear is that mainframe software licensing is “too complicated.”  I think software licensing is complicated on all platforms and from all publishers. For the IBM mainframe in particular, there are many license metrics that IBM offers.  When a new metric appears, it does not replace an old metric - it just adds it to the existing list!  

Mainframe teams need to learn the “rules” and “basics” of mainframe software licenses. They do not have to become level 5 experts but should understand enough to: 

   1. know the terminology
   2. formulate reasonable questions when needed
   3. understand answers without having to create a lengthy chain of emails or phone calls

At an introductory level, “computer” people should know that IBM mainframe software products fall into one of two categories:

  • MLC - Monthly License Charge
  • zOTC - zSeries One Time Charge

Here are some “basic rules” for each category:


  1. Monthly License Charge (MLC) means each product is billed monthly, in advance, on the first day of each month. The products are “leased” and not purchased.
  2. The monthly charge includes both the “right to use” and software maintenance for that month.
  3. Products are licensed on a machine basis (by CPU machine type and CPU serial number).


  1. One Time Charge (zOTC) means the products are purchased and not “leased”.
  2. The licenses are “perpetual” and the products can be used forever.
  3. Products are licensed across the Enterprise (within a country).

These basics should be understood by people dealing with mainframe software licensing. Each “rule” above is fairly straightforward by itself. It is important to know each one and how it relates to other “rules” in the category.

I would interested in knowing if this helps clarify some mainframe licensing questions. What do you think? And would you like to hear more about additional “basic rules?”