RE: 64-bit Architecture

["Al" <arl@q7.net>]

>> Are we talking difference like 68K -> PowerPC and VAX->Alpha?

>>Yep.  Arguably even more so, since IA-64 is a VLIW architecture,
>>IIRC.

It has been a while since some of the folks at HP and Intel explained this
to me but what I understand makes the design fast is that the compiler
supplies the CPU with information on the instruction stream so that better
choices can be made when executing instructions out of order and making
branch predictions.

If memory servers each 16 instructions are prefixed with a 8-bit context
tag. If two groups of instructions are examined by the CPU and their tags
are different then the CPU knows that the second group has no dependencies
on the first and could be executed at the same time the first group is still
being processed.