Well, at least you have the binary. Dis-assembly time! :-) Ha-ha-ha-ha-HAH! You _are_ an optimist! I'm not joking about the dis-assembly. Not to worry, it's not too bad (I had to do it to retrieve the source for the V6 RL bootstraps - and you've got symbols too), and you've got the V6 alloc.s to guide you - with luck, it did not get re-written between V5 and V6, and you may have minimal (no?) changes to deal with? I don't know which debugger V5 has (db or cdb); if neither, you can spin up a V6 and do the disassembly there. Do "db alloc.o > alloc.s" and then type '0?<RETURN>' followed by a whole bunch of RETURNs. (You can do plain 'db alloc.o' first, to see about how many CR's you need.) Next do a "nm alloc.o" to get as many symbols as you can. At that point, I would extract your prototype alloc.s from the emulated machine so you can use a real editor to work on it. (You should have a way to get files in and out of the simulated machine; that was one of the first things I did with my V6 work: http://www.chiappa.net/~jnc/tech/V6Unix.html although if you're using SIMH I don't know if that has a way to import files - a big advantage to using Ersatz-11, although one I didn't know about when I picked it.) You may need to go back and do a "xxx/" {with appropriate value for "xxx"} plus a few CR's to get static constants, but at that point you should have all the raw data you need to re-create the V5 alloc.s. Obviously, start by having your proto-allocV5.s in one window, and compare with the allocV6.s in another... like I said, you may luck out. The final step, of course, is 'as alloc.s', and then 'cmp a.out alloc.o'. Noel