Can someone explain the 64-bitness of these new Xeons?

Posted:
in Current Mac Hardware edited January 2014
I haven't followed much about 64-bitness has been implemented in the x86 world for quite a while. I seem to remember that Intel's Itanium didn't seem to be going much of anywhere, that it wasn't very compatible with the 32-bit x86 stuff, and the AMD's 64-bit offerings sounded a whole lot more appealing.



I also remember that the G5 does 64-bit data and addressing very well, quite seemlessly dealing with both 32-bit and 64-bit code.



So what's going on with the new Xeons in the Mac Pro? Has Intel emulated AMDs 64-bit ISA? Done their own new thing? Is there true 64-bit addressing, or is it some ugly sort of hack like the "segment registers" from the x86 past?

Comments

  • Reply 1 of 13
    chuckerchucker Posts: 5,089member
    Intel has licensed AMD's 64-bit, so x86-64 (working title) == AMD64 (AMD official name) == x64 (Microsoft name) == EM64T (Intel official name).



    So, Merom, Conroe, Woodcrest all have EM64T, which works the same as AMD64.



    This is not a clean 64-bit implementation like for PowerPC-64 or IA64 (Itanium), but it works well enough. It does, however, have some drawbacks. I won't get into details.
  • Reply 2 of 13
    AMD64 can run 32 apps at full speed. Itanium ran 32 bit a lot slower.
  • Reply 3 of 13
    placeboplacebo Posts: 5,767member
    Yeah well Itanium doesn't exist any more and Core 2 Duo whips AMD's ass, so I guess your attempts at injecting AMD fanboyism into this thread pretty much failed, huh?
  • Reply 4 of 13
    mdriftmeyermdriftmeyer Posts: 7,232member
    Quote:
    Originally Posted by Placebo


    Yeah well Itanium doesn't exist any more and Core 2 Duo whips AMD's ass, so I guess your attempts at injecting AMD fanboyism into this thread pretty much failed, huh?



    Perhaps, but you do a better job and sucking Intel's knob with your response.
  • Reply 5 of 13
    gene cleangene clean Posts: 3,481member
    Quote:
    Originally Posted by Placebo


    Yeah well Itanium doesn't exist any more and Core 2 Duo whips AMD's ass, so I guess your attempts at injecting AMD fanboyism into this thread pretty much failed, huh?



    Itanium does exist - it's called Montecito - and Core 2 Duo is a very nice processor, but "whips AMD's ass" is a little too far.
  • Reply 6 of 13
    thttht Posts: 3,114member
    AMD and Intel have a cross licensing agreement enabling them to implement each others x86 instruction sets, like Chucker said. Hence, AMD can implement Intel MMX/SSE instructions and Intel can implementent AMD's x86-64 implementation (Intel EM64T).



    EM64T is a 64-bit implementation capable of addressing 2^64 bits of memory with most hardware implementations supporting 2^36 to 2^48 bits of memory. That is, most hardware have obvious practical limitations and only support 64 GB to a lot more for clustering environments but usually less than 2^64, not the full 2^64. Woodcrest only goes to 2^36, 64 GB, and a vast majority of non-clustered machines will only have enough memory slots for 16 to 32 GB anyways.



    For a mixed 32/64 bit environments, most of the hit will likely come from increased memory requirements for running the required libraries to support both 32 and 64 bit applications. It shouldn't be a big issue with systems capable of 4 GB. I have to believe that the operating system emulates the 32 bit environment by up-chunking 32 bit apps to 64 bit, not like the mix-mode environment on the G5, which I believe runs 32 bit apps with true blue 32 bit ops. Don't really know for sure how it is precisely done, but you won't be seeing any performance deffiencies when running 64 bit for the vast majority of ops.
  • Reply 7 of 13
    cubitcubit Posts: 846member
    Thank you THT for answering Shenline's question. It helped some of the rest of us too.
  • Reply 8 of 13
    Quote:
    Originally Posted by Placebo


    Yeah well Itanium doesn't exist any more and Core 2 Duo whips AMD's ass, so I guess your attempts at injecting AMD fanboyism into this thread pretty much failed, huh?



    no but intel is useing amd64 in there chips
  • Reply 9 of 13
    kim kap solkim kap sol Posts: 2,987member
    Quote:
    Originally Posted by Gene Clean


    Itanium does exist - it's called Montecito - and Core 2 Duo is a very nice processor, but "whips AMD's ass" is a little too far.



    Well, people have different definitions of "whips" but I think it's safe to say that when you get 30% more performance *and* for much less power, you're "whipping" the competition. Show me a quad AMD system without a massive cooling system?
  • Reply 10 of 13
    shetlineshetline Posts: 4,695member
    Quote:
    Originally Posted by THT


    AMD and Intel have a cross licensing agreement enabling them to implement each others x86 instruction sets, like Chucker said...



    Thanks for the explanation (Chucker too).



    And no, I certainly wasn't and won't be expecting any system with 64-bit addressing to have a full 64-bit address bus anytime soon! I take 64-bit addressing to mean anything more than 32 bits, "capable of directly addressing more than 4 GB of memory." Few of us will be needing 2^64 bytes, or 16 exabytes, anytime soon. You could store several thousand copies of Google's entire database (on the order of around 2 petabytes of late) in 16 exabytes.



    16 exabytes, composed of $200 DDR 5300 1 GB modules, would cost $3.4 trillion. At 1.87 W of power consumption per module, total power needed would be 32 gigawatts. Combined US/Canadian power output from hydroelectric generators at Niagara Falls is currently around 4.6 gigawatts, so you'd only need around 7 Niagara Falls to power the 16 exabytes of RAM -- not counting power for a cooling system, but I suppose you could just let the water from one of the Falls you're using run through the system.



    If we allow 4.5 cubic inches per module (6" x 0.5" x 1.5") the RAM could be assembled into a cube 355 ft. (about 108 meters) along each side, which would make an impressively massive and squat 35-story building, even without any space added for hallways and elevators (or cooling pipes and cooling pumps for that matter).



    As the farthest corner of this cube would be about 256 ft from the center of the cube, even at the speed of light round-trip access time would be 520 nanoseconds, a terrible performance hit compared to the nanosecond-level access and per-byte transfer rates the RAM is capable of. Optimizing into a spherical rather than cubic arrangement would hardly make a difference.



    So, um, to make a long story short... I'm not holding my breath for the appearance of 16-exabyte PCs. I think we all might have to wait a while, and Moore's Law will likely run into a bit of trouble along the way.
  • Reply 11 of 13
    Nice post shetline



    Quote:
    Originally Posted by shetline


    You could store several thousand copies of Google's entire database (on the order of around 2 terabytes of late) in 16 exabytes.



    just a small typo correction - google's database is around two "petabytes"
  • Reply 12 of 13
    shetlineshetline Posts: 4,695member
    Quote:
    Originally Posted by Power Apple


    just a small typo correction - google's database is around two "petabytes"



    Noted and corrected. Thanks.
  • Reply 13 of 13
    placeboplacebo Posts: 5,767member
    btw, I made a thread about this but maybe it can be answered here, will Windows XP64 install on the Mac Pros do you think?
Sign In or Register to comment.