Efficiency Defined

Give Me Efficiency or Give Me an Empty CPU Socket!

You could always just remove your CPU to slash your power consumption, but no cancer gets cured that way.

Hi guys & gals!

Before I start talking the specifics of various computer hardware configurations, let’s get the definition of efficiency out of the way.  After all, computational efficiency is where it’s at!  That is the whole point of this blog.

Warning: Math Time (feel free to skip down a few paragraphs if you know this already):

Efficiency is a numerical ratio of two work or power quantities.  It has the general form of OUTPUT / INPUT.  Basically, it tells you how much desired work you got out of some process for a certain amount of input.  For a true mechanical or electrical efficiency, the units of both the numerator and denominator would be the same.  For example, our microwave at work generates 1200 watts of cooking power inside the machine, but draws 1488 watts at the wall.  Thus, it’s efficiency in terms of cooking power is: 1200 / 1488 = .806.  Multiply this fraction by 100 to get the efficiency percentage, and you see that our microwave is 80.6 % efficient at heating food.  Where did the rest of the energy go?  Well, in this case there was the power required to run the computerized guts, spin the turn table, spin the fan, light the light, etc.  There are also electrical losses in the circuits that get dissipated as heat into the microwave’s chassis.

Another good example is light bulbs.  In this case, we are looking at something called efficacy, not an electrical efficiency (but it is directly related), because the units in the numerator and denominator are going to be different.  It is possible, but less intuitive, to convert into a true efficiency ratio (visual power out / electrical power in), but I’m not going to go there because it hurts my brain.  Anyway, the good old 60 watt light bulb uses 60 watts (gosh) to create about 800 lumens of light.  By comparison, compact fluorescent bulbs use about 12-14 watts, and the new CREE LED bulbs use 9.5 watts.  Thus, the luminous efficacy of a 60 watt light bulb is 800 lm / 60 w = 13.3 lumens per watt.  On the other hand, the luminous efficacy of the awesome CREE LED bulbs (I have them everywhere in my house now) is 800 lm / 9.5 w = 84 lm/watt.  That is over 6 times more efficient than the old-fashioned tungsten filament bulb!  (Aside: you really should change out any 60 watt or 100 watt bulbs you still have in your house with CFL or CREE LED bulbs.  This is a great step towards negating your F@H carbon footprint! PLUS, IT  SAVES YOU MONEY!)

So, how does this relate to folding?  While, with F@H there is an accepted definition of work done, called Points.  The more work units complete, the more points you get.  Also, the faster your computer does the work units the more points you get (big time…it is exponential.  More on Stanford’s Points scheme later…).  So, to make this a power quantity (work done over time), we need to divide the # of points your computer is generating by the number of days it took to get those points.  Thus, we get to the most common rating of Folding@Home performance: The Points per Day unit (PPD).

We can obtain a rough “efficiency” of a F@H computer by dividing the PPD (scientific work output) by the electrical power (input) of the computer.  Note that this is really more of an efficacy rating (how effective something is at producing a desired output) but everyone on the interwebs calls it an efficiency so I will suppress the engineer in me and go with the flow of electrons on this one.

So, our F@H efficiency is PPD/Watt.  This is so central to this blog that I am going to say it again, for those skimmers who don’t like reading.

F@H efficiency is measured in Points Per Day / Watt!!!!

This is what we are concerned with.  Slow computers from 5 years ago still use a similar amount of electricity as today’s modern ones, but they are bricks when it comes to processing.  The amount of slow, crappy computers that are still running F@H is insane, and it is growing!  This is one of the main reasons why Folding gets a bad rap…the overall efficiency of the supercomputer as a whole is terrible.  We need to fix this!  Thankfully, Stanford & Sony have already ditched F@H on the Playstation 3.  This partnership was once one of the greatest boons to the F@H network, as back in the day the PS3’s were some of the fastest machines on the planet.  But, as computers got faster and the years went by, PS3’s became a poor choice relative to the new, super-efficient desktop processors and graphics cards.  Thus, F@H was removed as an option for Playstation users (much to their annoyance).  However, there is less management going on with the computer side of the F@H network (which is currently all of it).  If I want to, I can pull out my old Pentium 4 machine and get 100 PPD / 150 watts of power = 0.67 PPD/Watt!  But why would I want to spend money & kill the planet for that measly amount of performance?

I get the sense that you are likely getting the point by now, and thus I probably can stop rambling.  I can talk efficiency and specs all day (much to my wife’s annoyance).  The key takeaway is this:  Computers are always getting faster and more efficient.  F@H is as well, but is hindered by the amount of old computers that are stuck in yesteryear’s levels of efficiency.  We need to fix this.  We want to make our electrical contribution worth something.  WE WANT TO GENERATE AS MANY PPD/WATT AS POSSIBLE!  And that is exactly what we are going to do.  Over the next few posts, we’re going to talk in slightly less general terms about two things: how to Maximize PPD and how to Minimize Computer Power Consumption.  The latter is especially relevant to any computing project, even gaming or home computer use, so please feel free to read on even if you don’t plan to fold yourself.  Saving the planet and saving money by not using any more electricity than you need to accomplish a task is a worthy goal.  Tune in next time for the first hardware article: PC Power Supplies!


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