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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.
 
Return Value
 
The return value is zero in the AX register if the Interrupt 31h services
are available. Otherwise, the AX register contains a nonzero value.
 
Comments
 
Both standard- and 386 enhanced-mode Windows support the Interrupt 31h
services. Interrupt 31h services are only supported for protected-mode
programs.
 
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