Until June 1969 (a date known in the IBM mainframe community as "New World") IBM (with a very few exceptions) didn't even copyright its software, and did not charge for it. The price was bundled into the charges for IBM hardware. That's why you can find the source for pre-New World MVS and VM on the Internet, and run them in the Hercules S/370 emulator on a PC.
After New World, the combined pressure of the IBM mainframe clone manufacturers and the Justice Department antitrust lawsuit gave IBM the opening to unbundle software and begin charging what were then extremely high prices. (On the day of the New World announcement IBM released four "program products". A headline in a subsequent issue of _Computerworld_ read "SURPRISE! Software costs as much as a printer!". The reference was to one of the four program products, Generalized Information System (GIS), which had a monthly charge (running forever) of ~US$1200 (in 1969 dollars!), which was about the same as the monthly rental fee for a 1403-N1 1100 lpm printer.
Don't take the above price as exact; it's been 36 years ...
However ... even after New World many of the program products still offered an option for the customer to obtain the (copyrighted) source code. A few years later, however, the PHB contingent at IBM decided that it was a Bad Thing to allow mere customers to see the source code, with the result that IBM implemented the Object Code Only (OCO) policy.
IBM insisted that there was no need for customers to see the source or
*gasp* modify it to meet their organization's requirements because IBM was providing defined interfaces that gave customers all they needed. (Does this sound like the attitude of a certain software vendor in Redmond?)One other consequence of the OCO policy was that the customers could no longer debug the problems that were encountered when using the IBM products. One industry observer (Melinda Varian, I think, but I'm not sure and I've not talked to Melinda in many years) commented that with the OCO policy IBM had fired its most productive systems support staff: the unpaid (by IBM) customers.
Joe Morris