Yep, used to make heavy use of this back in my first post-college job writing database handlers in Macro11. Each transaction was just a table of subroutine addresses. This was about the last thing I had to do on a non-UNIX platform for years.

On Wed, Sep 13, 2017 at 11:33 PM, Alec Muffett <alec.muffett(a)gmail.com> wrote: A PDP-11 FORTRAN compiler I used back in the day was implemented this way, in part to make overlays easier (though I was young at the time, and never understood this bit). Overlays, as you may recall, were paging for systems that didn't support paging that swapped code (mostly) in/out as needed to fixed locations. The overlay manager was a quite important thing, since it automatically laid out the overlays based on calling sequences. Later versions would use MMU flipping tricks and had them aligned to 8k bounaries, but earlier versions were aligned to 512 boundaries to match the block size on the disk (since code was read-only, the OVL files were used to page code in). The Threading made the Fortran code smaller since the meat of the code was elsewhere, often in an area that wasn't overlaid... At least that's how my brain recalls things from 30-some years ago... Once I went away to college and was on a VAX or DECsystem20 (and later Sun3's and Sun4's), I swapped all this arcania out of my brain, so bit errors may have occurred before I just swapped it back in :) Based on Doug's description, it sure sounds familiar (and somewhat triggering it turns out, but in a good way)... There were also options to get co-routines, which is akin to a primitive 'threads' as we'd use the term today using an instruction that swapped the top of the stack and the PC, but that's different... Warner