Re: The real history of computer architecture: the short form

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Special-purpose compute engines are unavoidably rather expensive; gives a couple of interesting
directions to look in for the technology level that's actually
close to affordable.

The second-biggest Spartan3 chip has 96 18x18->36 multipliers, which gives
you eight 54x54 and a 72x72 to work with.  A medium-sized XC2VP50
Virtex2 Pro has 232 of the 18x18 multipliers, and a pair of PPC440
CPUs -- and sixteen Hypertransport links -- but probably costs as much
as a Madison 1300MHz/3MB (IE $2000 or so).  But I don't know what
speed you can clock that great array of multipliers at.

[note I've cross-posted this to comp.arch.fpga in case they know the
speed and cost details off the top of their heads; the idea is to
implement an array of double-precision FMA units on an FPGA, to see
how they'd compare to the few much-faster-clocked FMAs on high-end
CPUs.  I don't know how exotic the Spartan3/4000 or the XC2VP50 are]


Re: The real history of computer architecture: the short form
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I've done some back-of-the-enveloping.  It looks reasonable to make a
vector procesor that is about 1/2 to 1/4 the throughput of the Earth
Simulator vector processor in a large FPGA (eg, V2Pro), eg 8 lane, 8
FP MAC/cycle, but only ~250 MHz.

The interesting parts really come in not in the computation but in the
communication: how do you do a low latency, high throughput, flexible
network to connect a whole BUNCH of computing elements.  This is where
the FPGAs get interesting, with 3 Gbps SERDESes being standard and 10
Gbps SERDESes on the near-term horizon.  With a cut-through routing,
the latency per hop is fairly low (~20-30 cycles at the 3 GHz stream
clock), so a network could be made that isn't full connectivity like a
crossbar, but is rather fast and routed.

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Nicholas C. Weaver                       

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