Posts by Randall Churchill

Google goes after 3 billion with super satellite

Questionable math on latency figures

I am wondering how the author came up with latency figures of 1/2 second for geostationary and 1/20th of a second for low earth orbit? A round trip to geostationary orbit (36,000 km) should take 1/4 second rather than the 1/2 second the author claims it would take for a one way trip. A round trip for a low earth orbit sat (200-2000KM) assuming it was overhead at the time and taking the high end of the orbit range of 2000 KM would require roughly 1/75th of a second rather than a twentieth.

If starvation is something we might like to mitigate, perhaps we ought to stop subsidizing food production in wealthy nations so third world people can actually earn a living growing food. BY law, when the US ships food aid around the world, it is mainly food grown in the US, subsidized by taxpayers. Perhaps if we paid third world farmers to produce food rather than force them out of business via subsidies for wealthy nation farmers, starvation might not be such an issue?

Half-petaflop IBM BlueGene supercomputer plan announced

turing machine versus von neumann machines

I don't believe there was a turing machine built in 1942. In fact, turing machines/universal turing machines are merely artificial constructs, theories more or less. The work Alan Turing was involved with at Bletchley Park with the Enigma machine used equipment that was not general purpose and thus is not considered to be a programmable computer. It was not until 1948/49 than the Manchester Automatic Digital Machine (MADAM) was created and that was the first working example of the Universal Turing Machine. A standard instruction time of 1,800 microseconds, means it executed on average less than 600 instructions per second.

The so called von neumann machine is a computer design model implementation of a universal turing machine so really, there is no difference in architecture. As for WOW's assertion that a turing machine outperforms a von neuman machine....it really doesn't make sense nor is there much historical accuracy. The only machine one could compare the brit MADAM machine is with the EDVAC (Electronic Discrete Variable Automatic Computer) since ENIAC was not a stored program machine and would not be classified as a universal turing machine architecture. EDVAC required 2.9 milliseconds to perform a multiplication but only .864 milliseconds for an addition. Assuming only additions were performed one could expect a bit more than 1000 ops per second. A von neuman machine running 100s of megahertz in 1942 as WOW asserted just never happened. And thats all I have to say about that :-)

R