Johnny Billquist <bqt at softjar.se> writes: {...snip...} Well, this code runs on any Qbus, so all Qbus machines "benifit" from the code, not just the PDT-11. It's proably that on the Unibus, the speed penalty for a read-modify-write is less than reading a byte and pushing it on the stack, and then popping the stack and writing the word to the bus. Also, the DU-11 might respond much faster than the DUV-11. The buses are asynchronous, so the time for the execution is totally dependent on the speed of the device to respond to the bus cycles. OK. That wasn't clear from the choice of the symbol in the conditional. -- VAXman- A Bored Certified VMS Kernel Mode Hacker VAXman(at)TMESIS(dot)ORG Well I speak to machines with the voice of humanity.