In the 1970s, interacting with computer systems through display terminals became common. In small systems and technical computing, the RS232 serial interface with asynchronous, ASCII based protocols became the standard. Business systems based on IBM mainframe technology, in contrast, relied on high-speed synchronous communication over coaxial cables.

Nowadays, connecting an asynchronous serial terminal to a modern computer can easily be done using a readily available USB RS232 adapter. A 3270 style mainframe terminal, on the other hand, requires special hard- and software infrastructure to be brought to life. This presentation examines how terminals communicated with computers, how IBM mainframes implemented these interactions differently, and how a 3270 terminal can be used today to access both virtual and physical mainframes over the Internet.

Session Outline:

• Terminals, time sharing and interactive computing
• How one mainframe CPU served thousands of users in the 1980s
• The 3278 Terminal
• Implementing the coax protocol in a PIO state machine
• Using MicroPython to forward frames through WiFi
• The OEC virtual cluster controller written in Python
• Full circle - How the RP2xxx is a mainframe on a chip

https://github.com/lowobservable/oec https://github.com/hanshuebner/coax-tcp/tree/interface3/interface3