48H (BX=ffffH) determine largest available block
48H   allocate a block of memory
49H   free an allocated block of memory
4aH   resize (shrink/expand) a memory block

5800H query allocation strategy       5801H set allocation strategy
5802H query upper-memory link         5803H set upper-memory link
3306H See if DOS is in the HMA        INT 2fH 4axxH Suballocate in the HMA

XMS Services XMS memory/HMA control   EMM Services LIM-EMS memory
DPMI Services DOS Protected Mode Interface services

Accessing Upper Memory  how to allocate a UMB 
Program Startup & Exit  memory considerations when a program starts
CONFIG.SYS Commands     (DOS=, DEVICEHIGH=, etc. affect memory)

MCB Memory Control Block layout    PSP fields wNextSeg, et al. are relevant
INT 12H total conventional memory  INT 15H 88H total extended memory

Memory Management Functions