Yes, that's correct. (Bob's office was right around the corner from me - although I had very little knowledge of what his group was up to; I was too busy with other things.) I have this vague memory that his version was actually written in CLU? Can that be correct? It would make sense, since that group was so focused on CLU - but maybe not, see below. X must have been done after LCS got the 750 farm (on which we ran 4.1c, to start with) - although I don't know what kind of terminals they were using to run X on - we didn't have any bit-mapped displays on them, I'm pretty sure. Although maybe it was later, once Micro-Vaxes appeared? I have this vague memory that it was based (perhaps only in design, not code re-use) on a window system done at Stanford {looks}; yes, W (hence 'X'): https://en.wikipedia.org/wiki/W_Window_System The X paper listed there: https://dl.acm.org/doi/pdf/10.1145/22949.24053 doesn't say anything about the implementation, so maybe that vague memory/assumption that I had that it was originally written in CLU is wrong. Liskov's 'History of CLU' paper, which lists things done in CLU, doesn't mention it, so I must have been confused? Do any of the really early versions of X (and W) still exist? Noel