(→PCM and IBM: more detail on peripheral PCM)
==PCM and IBM==
The term PCM was originally applied to manufacturers who made replacements for [[IBM]] peripherals and later IBM mainframes.
The original example of PCM mainframes was the [[Amdahl Corporation|Amdahl]] [[Amdahl 470|470]] [[mainframe computer]] which was plug-compatible with the [[IBM]] [[System 360]] and [[System 370|370]], costing millions of dollars to develop. An IBM customer could literally remove the 360 or 370 on Friday, install the Amdahl 470, attach the same connectors from the peripherals to the channel interfaces, and have the new mainframe up and running the same software on Sunday night. Unfortunately, system status indicators for operators of the new system were very different, which introduced a learning curve for operators and service technicians.