[quasque]

It's interesting to see the real specification for this system call, as only the device availability subfunctions were widely known outside of Microsoft [1].

I wonder if many other hidden or deprecated functions are present in these releases.

[1] http://www.delorie.com/djgpp/doc/rbinter/id/65/27.html

[peteri]

At the time I seem to recall this was documented as being the SWITCHAR in config.sys certainly by MSDOS3.x this was well known and I seem to recall trying it out on MSDOS 2.x on a commodore pc clone (in Sweden) this would have been around 1985ish