• issued by DOS during keyboard poll loop
• indicates DOS may be carefully re-entered by TSR
• used by TSR programs to popup and make DOS disk I/O calls
• supported by OS/2 compatibility box
• default behavior is to simply perform an IRET
• any DOS functions above 0Ch may be called while in this handler
• INT 21,3F and INT 21,40 may not use a handle that refers to CON while in this handler

see also INDOS (int 21h,34h)