[saagarjha]

Actually, Objective-C's tagged pointers mostly rely on malloc's alignment guarantees.

[dan-robertson]

This is the case for most tagged pointer systems. Indeed most of them come from a time when 32 bit support was required.

[esmi]

Sure. Some software has to exist to make use of this system, for example something has to create the tag in the first place, and mall ic is a part of that, but the large address space is what makes them possible.