Science Quote by Ken Thompson

A whole philosophy of computing is hiding in that oddly clipped line: "avoid special IO for terminals". Ken Thompson isn’t just reminiscing about an implementation detail; he’s drawing a boundary against a recurring temptation in system design - the urge to treat one privileged device as so important it deserves its own rules.

In early Unix-building context, terminals were the front door to the machine. Giving them "special" input/output would have seemed practical, even inevitable. Thompson’s intent flips that instinct. He’s arguing for a uniform model where a terminal is not a sacred snowflake but just another file-like stream. The subtext is political as much as technical: special cases create priesthoods. If terminals require bespoke pathways, you get code that only a few people understand, interfaces that ossify, and software that can’t travel beyond the room it was born in.

The sentence’s spareness is part of the point. Thompson speaks like a builder who distrusts grand doctrine, yet the doctrine lands anyway: generality beats cleverness; clean abstractions outlast hardware fashions. "Special IO" is also a warning about the hidden costs of convenience. Short-term hacks accrete into long-term constraints, and constraints become culture - what developers assume is "normal."

Unix’s lasting influence owes a lot to this refusal to canonize the terminal. By not enshrining a single interactive device, the system left room for pipes, remote sessions, new UIs, and tools that compose. The future shows up; the special case breaks. Thompson chose not to build the breakage in.