Huh, I never knew that particular detail, and I’ve played with Windows quite a bit. But, with my modern OS developer hat on, I’d say it’s a bit lazy, not arbitrary.

> So if allocation granularity were finer than 64KB, a DLL that got relocated in memory would require two fixups per relocatable address: one to the upper 16 bits and one to the lower 16 bits.

…

> Forcing memory allocations at 64KB granularity solves all these problems.

It does, at the cost of silly limitations. A much nicer solution IMO would have been a way to ask for a 64kB aligned allocation for DLLs.