Obsolete DOS Functions

 The following INT 21H services are listed in Microsoft literature as not
 being supported by DOS 5.0+:

   18H (undocumented, original purpose unknown)
   1dH (undocumented, original purpose unknown)
   1eH (undocumented, original purpose unknown)
   20H (undocumented, original purpose unknown)
   3700H (undocumented; originally queried command-line switch character)
   3701H (undocumented; originally set command-line switch character)
   61H (undocumented, original purpose unknown)
   63H (undocumented, original purpose unknown)

   Notes: In general, the repeated warnings about using undocumented DOS
          services have been moot.  On all but the most obscure functions,
          Microsoft has maintained upward compatibility since the start.

          With DOS 5.0, Microsoft documented many "new" services and
          labeled them as "available with DOS 2.0 and all later versions."
          Such functions are flagged with â—„wasUndocâ–º in TECH Help!

See Also: Superseded DOS Functions
          DOS Function Index - by DOS Version
          DOS Versions (summary of differences from version to version)
          DOS Functions