Some Moore’s Law data points
I’m not a hardware guy, but here are some data points around the subject of Moore’s Law, quasi-Moore laws, and their bearing on random access times to disk and RAM. This line of inquiry is central to my argument favoring memory-centric data management.
Human-Computer Interaction cites 10 nanoseconds for RAM access time, 7 milliseconds for disk, and those figures are a couple of years old — that’s pretty supportive of my figure, namely the 1,000,000:1 ratio.
Don Burleson asserts that RAM speed has been 50 nanoseconds for decades. Hmm. I’m not sure what that means, since I’d think that RAM access speeds are bounded by clock speed. Of course, 20 megahertz is 50 nanoseconds per cycle, so some multiple of 20 megahertz would suffice to allow true 50 nanosecond access.
EDIT: I looked again, and he says that the 50 nanosecond limit is based on “speed of light and Proximity to CPU.” I’m even more confused than before, since light travels about 30 centimeters per nanocecond (at least in a vacuum).
A summary of a February, 2000 Jim Gray article makes some interesting points and claims in the same general subject area. One that stands out:
Storage capacity improves 100x / decade, while storage device throughput increases 10x / decade. At the same time the ratio between disk capacity and disk accesses/second is increasing more than 10x / decade. Consequently, disk accesses become more precious and disk data becomes colder with time, at a rate of 10x / decade.
Also, the disk capacity analog to Moore’s Law is sometimes named after Mark Kryder, and the network capacity version is attributed to George Gilder.
And finally — the fastest disks now made seem to spin at 15000 RPM. Those would take 2 milliseconds to spin halfway around, for the most naive estimate of their average random access time. And the naive estimate seems not to be too bad — depending on the exact model, they’re actually advertised with 3.3-3.9 millisecond seek times.
Comments
Leave a Reply