ask | dr. root

We know that a doubling of processor speed (frequency) does not result in a doubling of system performance. Why? Beacause improvements in memory latency have not kept pace with improvements in processor speed - in fact processor speeds are doubling every 2 years but memory speeds are doubling only every 6 years or so.

Throughput is impacted by both processor and memory speed; Sun recognised that having multiple threads in a processor could allow for greater throughput - as one thread is waiting for RAM, a second thread could execute and thus the waiting for RAM downtime is productive.

CMT - Chip Multi Threading allows for thread level parallelism to achiece unparalled scalability... within a chip.

Sun's CoolThreads technology, just announed this month, combines chip multi-processing (upto 8 cores per processor) and hardware muti-threading (upto 4 threads per core) . This is SMP on a single chip.

For more on this, please read this whitepaper - it's good!