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 ────────────────────────────────────────────────────────────────────────────── TSR/Popup Functions Service Groups DOS Functions