It’s a consequence of making the proof of work computationally intensive.
If computation is minimized in favor of random access to gigabytes of memory
(incurring long latencies), then mining will require large investments in RAM
but relatively little power.
Bitcoin mining is all computation and no memory.
Litecoin mining requires 128KB of memory per scrypt instance but only 1024
random accesses, with negligable latency.
Primecoin mining has a sieving and a modular exponentiation component, the latter of
which is pure computation, while the former requires a few megabytes of memory
(with non-random access).
Protoshares mining with Momentum requires 512MB but performs at least one complex SHA512
computation for each memory access, with a choice of algorithms some of which avoid random access.
The memory requirements above are not absolute but allow a trade-off between time and memory.
Guess which proof-of-work system achieves the following:
1) it performs only one very cheap hash computation for several random accesses to memory,
2) its memory requirement can be set arbitrarily and doesn't allow for any time-memory trade-off.
3) verification of the proof of work is instant
Runtime is completely dominated by memory latency. It promotes the use
of commodity general-purpose hardware over custom designed single-purpose hardware,
making mining more sustainable.
Fine, but you need to explain your last point. Why does it make mining more sustainable?