The 'V6' at MIT (actually, PWB1) never had an issue, but then again, its TTY driver (here: http://ana-3.lcs.mit.edu/~jnc/tech/unix/mit/dmr/tty.c if anyone wants to see it) was heavily re-written. But from the below, it's almost certainlynothing to do with the TTY code... Good test. If you all want to chase this down (I can lend V6 expertise, if needed), I'd say the first step is to work out whether it's the application, or the system, losing the characters. To do that, I'd put a little bit of code in write() to store a copy of data sent through that in a circular buffer, along with tagging it with the writing process, etc. Once you figure out where it's getting lost, then you can move on to how/why. Yeah, but it's super-trivial to add /23 support to V6: http://gunkies.org/wiki/Running_UNIX_V6_on_an_-11/23 The only places where change is needed (no LKS register, no switch register, and support for more than 256KB of main memory - and that one one can get by without), it's hard to see how they could cause this problem. No, we never ran than on a /23 BITD (no need, no mass storage); and I have yet to bring the V6+ system up (although I have all the bits, and intend to, at some point, to get its TCP/IP running). I've been using stock (well, hacked a bit, in a number of ways - e.g. 8-bit serial line output) V6. Noel