Why SOI

Article: AMD's Bulldozer Microarchitecture
By: David Kanter (dkanter.delete@this.realworldtech.com), September 6, 2010 5:19 pm
Room: Moderated Discussions
someone (someone@somewhere.com) on 9/6/10 wrote:
---------------------------
>DC (a@b.c) on 9/6/10 wrote:
>---------------------------
>>someone (someone@somewhere.com) on 9/5/10 wrote:
>>---------------------------
>>>DC (a@b.c) on 9/5/10 wrote:
>>>---------------------------
>>>
>>>>Well AMD are using more or less the same process technology as IBM, and IBM have
>>>>been taking the speed racer route recently. If I recall correctly, doesn't SOI reduce
>>>>leakage current?
>>>
>>>There are two major sources of leakage in modern MOS
>>>processess and a dozen or so minor ones. SOI fixes one
>>>of the minor ones accounting for roughly 1% or less of
>>>total leakage, depending on the design.
>>>
>>
>>If the differences is so small, why do IBM and AMD bother with SOI when bulk silicon is cheaper?
>
>The total cost of a MPU is the sum of its incremental
>manufacturing cost and its amortized NRE (the cost to
>design the MPU divided by the total units made).
>
>Intel makes and sells about 4x more MPUs than AMD
>and maybe 250x more MPUs than IBM.
>
>For *equal* design effort SOI may give you 10% higher
>performance than bulk at say 10% higher manufacturing
>cost. With more design effort (higher NRE) you can make
>up for the inherent process disadvantage of bulk with
>more manually intensive critical circuit optimization
>and interconnect tuning.
>
>For IBM the choice is clear, it makes far fewer MPUs
>than Intel and manufacturing cost is dwarfed by the
>amortized design cost. Spending more on making MPUs
>using SOI to save on design costs is a clear win for
>them. Intel on the other hand makes so many MPUs that
>manufacturing costs dominate. Spending more on NRE
>to get top performance in cheaper bulk is well worth it.
>AMD OTOH is in a difficult spot. It can't afford to spend
>as much on design as Intel but it competes against
>Intel largely on price so using SOI hurts.

I think the point about relative volumes are critical. I'd also point out that almost every high volume device (except for the consoles) are done on bulk. GPUs, cell phones, cable modems, routers, etc. all use bulk. Even Bobcat is done in bulk.

One advantage of SOI is that it improves SER immunity. For IBM, that's quite nice and it helps for AMD's server parts...less important for clients.

I think AMD is using SOI because IBM is using SOI (and IBM does most of the manufacturing research, while GF does more of the development). So they kind of have to follow IBM's lead (not that this is a bad thing) unless they want to do a lot of research themselves. Moreover, AMD has already made the investment in tools/training, the performance advantage is nice, etc.

David
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        Dispatch groupsredpriest2010/08/31 08:46 PM
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          Dispatch groups?2010/09/01 10:03 AM
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            Bulldozer versus Westmere single threaded performanceJack2010/09/01 10:08 PM
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          Bulldozer versus Westmere single threaded performanceMark Roulo2010/09/01 09:14 AM
            Bulldozer versus Westmere single threaded performanceRichard Cownie2010/09/01 09:33 AM
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        There is no 20% penalty of two threads compared to single core - it's 10%Azazel2010/09/03 12:35 AM
          There is no 20% penalty of two threads compared to single core - it's 10%?2010/09/03 02:40 AM
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            There is no 20% penalty of two threads compared to single core - it's 10%Azazel2010/09/03 07:31 AM
          There is no 20% penalty of two threads compared to single core - it's 10%MS2010/09/03 06:27 AM
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            Don't read too much into it...DC2010/09/05 11:07 AM
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                    Bulldozer article onlineEduardoS2010/09/06 06:21 PM
                    Bulldozer article onlineanon2010/09/06 06:26 PM
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                        Bulldozer article onlineanon2010/09/06 10:49 PM
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              Bulldozer article onlinesomeone2010/09/06 08:53 AM
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              Bulldozer article onlineJack2010/09/07 10:16 PM
                Bulldozer article onlineslacker2010/09/08 08:05 AM
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                  Bulldozer article onlineJack2010/09/12 08:26 PM
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                    FP ADDs are not that fastEduardoS2010/09/30 01:41 PM
                      FP ADDs are not that fastrwessel2010/09/30 02:41 PM
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    FMACs can be ganged together, confirmed already by JF (link inside)David Kanter2010/09/09 07:32 AM
      FMACs can be ganged together, confirmed already by JF (link inside)Triskaine2010/09/09 07:48 AM
        FMACs can be ganged together, confirmed already by JF (link inside)David Kanter2010/09/09 08:11 AM
          FMACs can be ganged together, confirmed already by JF (link inside)arb2010/09/09 09:22 AM
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          FMACs can be ganged together, confirmed already by JF (link inside)gruehunter2010/09/09 01:08 PM
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              FMACs can be ganged together, confirmed already by JF (link inside)redpriest2010/09/09 09:56 PM
                FMACs can be ganged together, confirmed already by JF (link inside)Anthony2010/09/10 11:59 AM
                  FMACs can be ganged together, confirmed already by JF (link inside)someone2010/09/10 12:11 PM
      FMACs can be ganged together, confirmed already by JF (link inside)Alex2010/09/10 12:04 PM
    FMACs can be ganged together, confirmed already by JF (link inside) -- Oh No JFFritz2010/09/22 04:37 AM
      FMACs can be ganged together, confirmed already by JF (link inside) -- Oh No JFAnthony2010/09/22 11:01 AM
        FMACs can be ganged together, confirmed already by JF (link inside) -- Oh No JFDavid Kanter2010/09/22 11:22 AM
          FMACs can be ganged together, confirmed already by JF (link inside) -- Oh No JFanon2010/09/22 12:19 PM
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          FMACs can be ganged together, confirmed already by JF (link inside) -- Oh No JFredpriest2010/09/23 05:47 PM
      FMACs can be ganged together, confirmed already by JF (link inside) -- Oh No JFAnthony2010/09/22 11:01 AM
  Bulldozer article onlineMarcal2010/09/29 03:13 AM
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