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Another Limit: Speed of Light!

1 Tflop/s, 1 Tbyte sequential machine

r = 0.3 mm

  • Consider a hypothetical 1 Tflop/s sequential machine:

    • Data must travel some distance, r, to get from memory to CPU.

    • To get 1 data element per cycle, this means 1012 times per second at the speed of light, c = 3x108 m/s. Thus r < c/1012 =

      • 0.3

        mm.

  • Now put 1 Tbyte of storage in a 0.3 mm x 0.3 mm area:

    • Each bit occupies about 1 square Angstrom, or the size of a small atom.

  • No choice but parallelism

COMP 422, Spring 2008 (V.Sarkar)

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