The Allocate Descriptors function (0000h) can allocate an array of contiguous
descriptors, but only return a selector for the first descriptor. The value
returned by this function can be used to calculate the selectors for subsequent
descriptors in the array.
In:
AX = 0003h
Out:
always successful:
carry flag clear
AX = selector increment value
Notes:
The increment value is always a power of two.