Conversational Monitor System
CMS runs as a "guest" operating system in a private virtual machine created by the VM control program.This approach has remained consistent through the years, and is based on: More details on how CMS interacts with the virtual machine environment can be found in the VM and CP/CMS articles.Personal customization is done by a standard shell script file named "PROFILE EXEC", which sets up user-specified environmental defaults, such as which disks and libraries are accessed.The 3270 played a strategic role in IBM's product line, making its selection a natural choice for large data centers of the day.Commercial time-sharing users, an important segment of early CP/CMS and VM sites, relied on such devices because they could connect via 300- or 1200 bit/s modems over normal voice-grade telephone circuits.These asynchronous terminal controllers assembled a line of characters, up to a fixed maximum length, until the RETURN key was pressed.However, these devices rarely competed for 3270 users; IBM maintained its dominance over mainframe data center hardware purchase decisions.This approach, preferred by IBM, led to the development of entirely different user interface paradigms and programming strategies.The difference is apparent when comparing the atomic transaction approach of dominant CICS with the interactive, stream-oriented style of UNIX.It was not uncommon to have hundreds (later: thousands) of concurrent CMS interactive users on the same VM mainframe, with sub-second response times for common, 'trivial' functions.