INT 2F - PCED/VSTACK - INSTALLATION CHECK
AX = 48C1h
BL = 00h
Return: AX = 0000h if installed
BX = VSTACK resident segment
Program: VSTACK is a resident backscroll utility included as part of the PCED
package by Cove Software
Note: chains if BL <> 00h on entry
SeeAlso: AX=48C0h,AX=48C2h