The IBM Type-III Library (also: Type-III software, Type-III product) was software provided by IBM to its customers, available without charge, liability, or support, and typically (perhaps always) in source-code format. Well-known examples are for mainframe software; IBM may have also used this same classification on smaller systems.

IBM also distributed other systems in source code form. Most early operating systems were shipped in this way. Source distribution of the VM family of operating systems continued for several decades after it supplanted CP/CMS from the Type-III Library, and TPF was always distributed in source form, apparently continued today with z/TPF. Unlike Type-III software, such systems were supported by IBM.

Uncertain scopeEdit

Conflicting descriptions of Type-III software are found in otherwise credible sources.

  • An IBM publication on CP/CMS characterized IBM's Type-III products as "IBM employee contributed" and further characterized them as follows:
[The software] has not been submitted to any formal test. Type III Programs are provided by the IBM Corporation as part of its service to customers, but recipients are expected to make the final evaluation as to the usefulness of the programs in their own environment. There is no committed maintenance for Type III Programs, nor does IBM make any warranty, expressed or implied, as to the documentation, function or performance of such programs.[1]
  • Another source on early CP/CMS history describes Type-III software as "customer contributed" and states that CP/CMS "was 'snuck' into the Type-III library": "the public release was officially submitted by Lincoln Labs because IBM was no longer allowed to make it freely available."[2]

A possible inference is that both employee-submitted and customer-submitted software wound up in the Type-III library, and that the significance of the list was to define IBM's responsibility in regard to maintenance and support, rather than to identify the original submitter of the software.

The Type-III library was eventually replaced by several different product designations. Programs contributed by customers were known as "Installed User Programs" (IUPs) and those developed by IBM employees as "Field Developed Programs" (FDPs). The "field developed" moniker was something of a misnomer, as quite a few FDPs were written by employees in the IBM programming groups rather than by field personnel.


Some of the many Type-III programs offered by IBM include:


  1. An introduction to CP-67/CMS, IBM Cambridge Scientific Center Report 320-2032, May, 1969. [as quoted in M. Varian, VM and the VM community: Past, present, and future, available on-line here
  2. T. Van Vleck, The IBM 360/67 and CP/CMS
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External linksEdit

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