4 ms·

Since the speed-of-light delay for 100 feet is 100 ns, and SSD latencies are on the order of 10-100 us, this shouldn't be a fundamental issue. Maybe it's caused

by uvdiv 14y ago

Since the speed-of-light delay for 100 feet is 100 ns, and SSD latencies are on the order of 10-100 us, this shouldn't be a fundamental issue. Maybe it's caused by the latency to the disk cache (DRAM)? In which case perhaps you could separate that from the disk, and move it closer to the CPU.

Retric 14y ago
100 feet / speed of light = 101 nanoseconds, round trip that's 202 nanoseconds, but electricity is ~66% of speed of light ~= 300 nanoseconds or .3us. (Fiber is also ~1/3 slower than the speed of light both because it's not a vacuum and the path is not strait.) Now 10 us vs 10.3 us might not sound like much but it's still 3% slower. And it get's worse when you look at high end DRAM based SSD's which can be faster than 10 us.
- ghshephard 14y ago
  "but electricity is ~66% of speed of light" According to Wikipedia, it depends on the insulation: == SNIP == Propagation speed is affected by insulation, so that in an unshielded copper conductor ranges 95 to 97% that of the speed of light, while in a typical coaxial cable it is about 66% of the speed of light. == SNIP == For LMR-400 (a very common cable for Ham Radio) - the Velocity Factor is about 85% according to http://www.febo.com/reference/cable_data.html http://www.febo.com/reference/cable_data.html The net-net is, that there are opportunities to get closer to the speed of light if latency is really, really important.
  - marshray 14y ago
    At data rates, transmission lines are used in copper. This is why CAT-5e has higher requirements on the twisted pairs than CAT-3 (or plain old phone line). 66% turns out to be a surprisingly consistent approximation for both copper and fiber.
bradleyjg 14y ago
At 2Ghz the speed of light in a vacuum delay is a clock cycle every 15cm. Current fiber and copper transmission is about 70% of c, so that's a clock cycle every 10.5 cm. A few clock cycle might not matter for bulk storage, but Intel is also talking about separating main memory from individual processors. There individual clock cycles do matter. Witness the rise of low latency premium RAM.
- geon 14y ago
  We are already doing that, in many steps.

by uvdiv 14y ago

Retric 14y ago

100 feet / speed of light = 101 nanoseconds, round trip that's 202 nanoseconds, but electricity is ~66% of speed of light ~= 300 nanoseconds or .3us. (Fiber is also ~1/3 slower than the speed of light both because it's not a vacuum and the path is not strait.) Now 10 us vs 10.3 us might not sound like much but it's still 3% slower. And it get's worse when you look at high end DRAM based SSD's which can be faster than 10 us.

ghshephard 14y ago
"but electricity is ~66% of speed of light" According to Wikipedia, it depends on the insulation: == SNIP == Propagation speed is affected by insulation, so that in an unshielded copper conductor ranges 95 to 97% that of the speed of light, while in a typical coaxial cable it is about 66% of the speed of light. == SNIP == For LMR-400 (a very common cable for Ham Radio) - the Velocity Factor is about 85% according to http://www.febo.com/reference/cable_data.html http://www.febo.com/reference/cable_data.html The net-net is, that there are opportunities to get closer to the speed of light if latency is really, really important.
- marshray 14y ago
  At data rates, transmission lines are used in copper. This is why CAT-5e has higher requirements on the twisted pairs than CAT-3 (or plain old phone line). 66% turns out to be a surprisingly consistent approximation for both copper and fiber.

bradleyjg 14y ago

At 2Ghz the speed of light in a vacuum delay is a clock cycle every 15cm. Current fiber and copper transmission is about 70% of c, so that's a clock cycle every 10.5 cm. A few clock cycle might not matter for bulk storage, but Intel is also talking about separating main memory from individual processors. There individual clock cycles do matter. Witness the rise of low latency premium RAM.

geon 14y ago
We are already doing that, in many steps.