Offset Size Contents
+0       4  pfData       address of the instance data (or 0000:0000 if
last record in the list)
+4       2  wSize        size of the instance data, in bytes
6               size of an SwInstanceItemRec structure

pfData  this is the address of a data area which needs to be saved on
each task switch and restored when that task is reactivated.
SwInstanceItemRec structures are organized as a sequential
list.  When pfData is 0000:0000 it indicates the end of the

wSize  the size of the data area, in bytes. Note that the maximum
size is 64K; but you can create two or more of these
structures to identify a region that is larger.

This structure is pointed to by the pfarInst field of an SwStartupInfoRec
used in INT 2fH 4b05H (identify instance data).    It is part of the
system that allows programs to be reentrant across multiple tasks by
reserving memory areas for buffers and variables.

INT 2fH 4bxxH (switcher functions)
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