Interrupt 2Fh Function 1686h

mov     ax, 1686h   ; Detect Interrupt 31h Services
int     2Fh         ; multiplex interrupt

or      ax,0
jz      int31_avail ; ax is zero if interrupt 31h services available

Detect Interrupt 31h Services (Interrupt 2Fh Function 1686h) determines whether a set of protected-mode functions are available for use by protected-mode applications. Applications use the Interrupt 31h services to allocate and manage protected-mode memory.

This function has no parameters.

• The return value is zero in the AX register if the Interrupt 31h services are available. Otherwise, the AX register contains a nonzero value.

Both standard- and Windows support the Interrupt 31h services. Interrupt 31h services are only supported for protected-mode programs.