No Program counter just means the next location to execute does not default to P+1. The current micro-location is known and can be pushed on a stack with a "subroutine return" address bit flipped to create a return address when the subroutine returns. Many Prime Computers used the same tactic in their firmware next address units. Requires good software to allocate the firmware efficiently. Can't have two subroutine calls in a row without additional creativity unless you want to ping-pong forever.
You know, a decade or so back there was a phenomena of naming every one-researcher lab a "Center of Excellence" in this, that or the other thing. As though anyone ever started a "Center of Good Enough" or "Center of Mediocrity". This trend seems to have diminished. Thank heavens: many of these Centers weren't much more than a letterhead.
Precisely... if you are going to take up real estate with wide busses, then you may as well get everything you can for it. And that's more than addressing, branching, vector fields, and so on. There's only time, and space... if we are pushing the timing limits at the moment, then we can push out the space envelope as well.
128 bits isn't all about memmory addressing. Many fields like Cryptography and GPS can certainly benefit from wider registers, particularly a true 128 bit, quad precision floating point capability. But simple, everyday operations can also benefit as well. High clock rates and multiple cores aren't the only roads to performance increases. Just think about string matching 16 bytes at a time!
In addition to SIMD and vector operations, a wider instruction word allows you to build-in hardware n-way branches, where n might be 4 to 256. The wider word, ultimately, allows you to trade off space for time.
Why do you want 128-bit address widths?
32 bits only gives you 4Gbytes which is too small for servers.
64-bits gives you 1.8x10^19 bytes. That's more than 2Gbytes for every person on the planet and is probably more than is needed to address all the RAM in existence.
It is going to be a long time before we need a bigger address bus and it certainly is not worth the overhead for the foreseeable future.
NASA's Orion Flight Software Production Systems Manager Darrel G. Raines joins Planet Analog Editor Steve Taranovich and Embedded.com Editor Max Maxfield to talk about embedded flight software used in Orion Spacecraft, part of NASA's Mars mission. Live radio show and live chat. Get your questions ready.
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