LocalAlloc took around 11 seconds, but my computer seemed to slow down, HeapAlloc took around 10 seconds

Definitely stick with HeapAlloc for smaller allocations, forget all about Local/GlobalAlloc rubbish, and consider VirtualAlloc if you need huge (several megabytes) allocations, or need the specific alignment/protection stuff VirtualAlloc has to offer.

Oh, there's a very few uses for Local/GlobalAlloc though, iirc the clipboard APIs require it, and CreateStreamOnHGlobal... because when not allocating "FIXED" or "GPTR", even though l/galloc use HeapAlloc internally, they add some extra control structure, and you can end up with corrupted heap structures if you don't play by the rules.

i will be quite clear after you figure out what difference between heap and stack.

My wild wild guess is that HeapAlloc receives by its heap handle s.th. without effort, something that GlobalAlloc needs to look up or create on every call.

kandamun: stop making wild guesses, and disassemble kernel32.{Local,Global}Alloc

No, i'm too lazy and i have my own bugs to disassemble