Does anyone reading this list still write code to be run under RT-11? When a program has a bug, what do you use to find the problem? For debugging programs, SD: seems the most efficient way, especially when a Mapped Monitor is being used. Alternatively, ODT (VDT when Multi-terminal Support is included in the RT-11 monitor) can be LINKed into the program. Recently, I have been considering enhancements to the SD: variant, SDHX.SYS, which would reduce the Low Memory required along with adding an additional feature which is part of Ersatz-11. Specifically, SET PCLOG ON requests the Ersatz-11 emulator to save the addresses of the last 64 instructions that were executed. The the command SHOW PCLOG displays all 64 addresses at the users request. I would appreciate a response from anyone still writing and debugging programs that run under RT-11 and which debug package is being used along with the advantages and disadvantages that have been found. One big advantage of SDHX.SYS (actually all of the SD: variants) is that the user can request an automatic display of all of the register contents every time that a breakpoint occurs. The display occurs at the top of the screen each time the breakpoint takes place. The VT100 escape codes are then used to scroll down the screen and display each instruction in turn as it is about to be executed. One big disadvantage of SDHX.SYS is that it freezes the system completely, including the clock interrupts. The big advantage of VDT is that other jobs are able to continue running, but no other information is easily available when the program is stopped at a breakpoint. I would appreciate any response. Jerome Fine