I'm surprised they need so many bits.. you really just need to know if the item is an object (so the type can be embedded in the object), or a primitive type.

I'm surprised they need so many bits.. you really just need to know if the item is an object (so the type can be embedded in the object), or a primitive type. But there are not so many primitive types. Some dynamically typed systems put the tag at the beginning of a page: so all items of a particular type are allocated out of a page tagged with that type. You don't waste any bits from the pointer or data, but you do have to do some masking and worse, a remote memory access to get the type. Probably safest and fastest to do something like: struct { int type; union { char *s; int n; double d; }};