On 2013-01-06 18:13, Lee Gleason wrote: .IF DF L$$SI1 MOVB @(R5)+,-(SP) ;;; COPY CHARACTER FOR WORD MOVE MOV (SP)+,(R4) ;;; (SAVES 85 USECS ON PDT-11) .IFF ; DF L$$SI1 MOVB @(R5)+,(R4) ;;; OUTPUT A CHARACTER .ENDC ; DF L$$SI1 OK, I'll bite. Why is moving a character in the deferred location in R5 to the stack and then, from the stack to the address in R4 faster than just going from the deferred R5 location to the R4 address? -- I'm even more curious what a PDT-11 optimization is doing in an RSX driver...was there at one time an RSX product product planned for the PDT family? I'm not at all surprised to learn that RSX ran on the PDT-11. RSX can run on pretty much any PDP-11, as long as you have atleast around 50K of ram. That's about the lower limit, I'd guess. No other hardware frills or features required. I'm curious if the PDT-11 supported booting over the DUV-11. That would have made it a pretty nice netbooted, diskless RSX machine. Otherwise I'd suspect the most common use was just 11S booted from whatever locally. But an unmapped 11M system is a possibility, I guess. Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol