> 2 bits of tags, and they're thinking general purposes (e.g. GC) as well as security. That's big, something we haven't seen in hardware since Lisp Machines, to my knowledge.

The IBM AS/400 or whatever it is called this week uses tags too for security. (A bit is flipped if a pointer is written too thereby preventing changing pointers.) The PowerPC chip has optional support for tags because of this.

Source: http://www.amazon.com/Inside-AS-400-Second-Edition/dp/188241...

The apps and most of the OS are distributed as the equivalent of high level byte code using 128 bit pointers. Once run it gets translated into the local machine code.

For anyone unfamiliar with the AS/400 and predecessors I highly recommend the expensive book by Frank Soltis who is largely the architect of it. Many things were done very differently than other operating systems and applications. http://www.amazon.com/Inside-AS-400-Second-Edition/dp/188241...

Indeed, OS/400 is just wonderfully advanced under the hood. Get one of the cheap used copies of this book for a lot more: http://www.amazon.com/Inside-AS-400-Frank-Soltis/dp/18824196...