INT 21 - DOS 2+ internal - CREATE CHILD PSP
AH = 55h
DX = segment at which to create new PSP
SI = (DOS 3+) value to place in memory size field at DX:[0002h]
Return: CF clear if successful

Notes:  creates a "child" PSP rather than making an exact copy of the current
PSP; the new PSP's parent pointer is set to the current PSP and the
reference count for each inherited file is incremented
(DOS 2+) sets current PSP to DX
(DOS 3+) marks "no inherit" file handles as closed in child PSP
SeeAlso: AH=50h

See also: 2126

2155 - DOS 2+ internal - CREATE CHILD PSP