[int_19h]

> windows def allocator

Which one of them? These days it could mean HeapAlloc, or it could mean malloc from uCRT.

[carey]

malloc in uCRT just calls HeapAlloc, though? You can see the code in ucrt\heap\malloc_base.cpp if you have the Windows SDK installed.

Programs can opt in to the _segment_ heap in their manifest, but it’s not necessarily any faster.