Saturday, June 11, 2011

power consumption - blacker the better

Here I present an obvious fact that is easily overlooked.

Having a large screen monitor, it is easy to save on power consumption - just work in terminal more often.

I write this article on a 24 inch Iiyama Prolite B2403WS, which is rated at 65 watts maximum (specification given in the manual)

However that that 65 watts is a peak load when watching a high definition movie.

Running a normal graphical desktop and switching between programs will use nowhere near that amount, and uses 30->45 watts

( measured at the electricity outlet - monitor usage only )

GNU / Linux types who are skilled in command line use, can easily cut that down to 15 watts.

A black background terminal (the sort Linux folks prefer), will see the monitor consume 15 watts under normal use.

That might increase to anything up to 24 watts, when watching fast console output such as strace, or significant compile output.


What about a laptop - can I save there also?

Same principle applies. Particularly for 17 inch or 15 inch laptops.

It is easy to stretch your battery life, as a full graphical display that is being constantly updated, is taking a good dose of your battery and feeding it to the flat panel display half.

Certainly when you get to the last hour of your laptop battery, switch off anything strictly unnecessary, and that includes a graphical display (unless you really need it).

Have 30 minutes of battery time left, and working in terminal but within Xfce or Gnome?

Switch to console using Ctrl+Alt+F1 or Ctrl+Alt+F2 and carry on working there.

Your power management daemon is still sitting in the background, and should shut down when % battery life becomes critical.

But you just doubled your working time remaining from 20->30 minutes to 40->60 minutes, by dropping down the display to almost idle :)


What about the entire system - how much does an oldish desktop use?

In preparation for a newer six-core AMD FX-6110 sometime next year, my desktop parts have been passed on, and gone backwards to an ancient AM2 Athlon, for the next 6 -> 12 months.


It is not very power efficient (by todays standards), but it does okay for a 2GHz three year old.


The third digit of the CPU model number for AMD Athlon processors details the power rating. ADD... or ADO... or ADV... for Athlon 64 dual core processors says 35, 65, 89 watts respectively. Sometime ADA will be used to represent 89 watts.


Not having the model number to hand, but being fairly certain the processor is from the 'Windsor' family, my measurements were as follows:
  • 70 graphical desktop (not enough usually to stress either core above 1Ghz)
  • 85->90 dual cpu compression task - both cores maxed - system hits 90w
  • 70 watts when idle / grub
  • 90 system bootup - cpu is normally stressed during first 30 seconds bootup
Note: These are at plug measurements that exclude the monitor, and include the motherboard, hard drive, and dedicated Ati 3450 graphics, giving total usage 70->90 watts, with 70w being more likely under normal load.


The processor based on my measurements is either 90 watts peak (but overrated in documentation versus real usage), 65 watts peak, or 35 watts peak.

My guess is cpu is 65 watts peak, and see little point in pulling the cooler off the cpu to check.


Power consumption of this system at 70 watts is acceptable in my opinion.


The Samsung Ecogreen hard drive is helping - it uses very little compared to other hard drives > 1TB.


If I were not planning on and upgrade to FX-6110, my other choice would be to replace this entire system with a socket FM1 combined Cpu+Ati graphics.

Such a socket FM1 system, when connected to that Samsung Ecogreen, would probably tick over at less than 30 watts!




Using 1 kilowatt of power and that AM2 system + monitor:


In the UK right now 1 kilowatt of power (for an hour) costs around £0.20 rewritten 20 pence.


Translating that in power terms that could be considered 100 watts for ten hours.


This system is used for business and word processing, and there is very little gaming / movie watching in any 1 month.


System+Monitor uses 110 watts in normal use.

So that says that running that system for 9 hours every weekday would cost £1.


I can easily make an effort to reduce that power consumption further, by using terminal as describing earlier.




Notes and Further Reading:


If you are conscious of your power usage, and are thinking of buying a new larger hard drive, then do consider the Ecogreen or other lower power alternatives.

Sata drives are so fast these days that reducing power by having a larger disk cache, but variable / lower spin speed is an option (Ecogreen)


In 2012 and 2013, a 256GB solid state drive will be much more affordable, so there is an additional option for upgraders there also.

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