I have used TECO on and off for 30 years (mostly off for the past 15 years). The latest version that I can find which was released for RT-11 is TECO V36. This version was released with V04.00 of RT-11 in 1980. The TECO command "EO=" confirms that the version is V36. About a year ago, I found some source code for TECO V36 which assembles to V36 when asked via "EO=", but the TECO.SAV file is significantly different from the version released with V04.00 of RT-11 in 1980. The version based on the source code that I found is 51 blocks long and it uses more memory. The version from RT-11 V04.00 is just 50 blocks long and has a much smaller root section. Probably most of the code is the same, just that some of the code that is in the root of the version for which I have the source has been moved to an overlay. Does anyone have or know where I might find the actual source code for TECO V36 that was released with V04.00 of RT-11 in 1980? If it is just almost identical, that would be sufficient since it is usually possible to easily make a few modifications to obtain the identical TECO.SAV when the differences are minor. Often, the differences seem major since they can be the result of a single extra word (plus or minus) which shifts the rest of the code and makes an exact comparison impossible. But those changes are easy to find and correct if the knowledge and experience of what to do is available. Since the TECO V36 released with V04.00 of RT-11 is now 31 years old and I have not heard of any bugs, I have much more confidence in its reliability as opposed to the version for which I have the source code. Jerome Fine