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How much electricity does a laptop use compared to a desktop?

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This question is too broad, this depends on the hardware of both. –  Tom Wijsman Jun 19 '10 at 18:52
    
I'm interested in comparing a Macbook Pro to an AMD64 with three hard drives, an external video card installed, and two flat screen monitors. –  Phenom Jun 19 '10 at 21:45
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closed as off topic by random Sep 2 '12 at 1:01

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4 Answers

up vote 2 down vote accepted

In specific, my home-brew gaming rig (Core 2 duo, 8800GTS) runs about 350 watts when running games, and 250 idle (includes monitor). My old Intel Dual Core (not Core 2) laptop using integrated graphics drew around 25 watts when not charging the battery. 45-55 watts when charging. I haven't had a chance to check the draw on the new i5 laptop.

But that's just two datapoints.

Discrete graphics markedly increases power usage on laptops.

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It's really dependant on which specific hardware parts you have but you have to think about the fact that the two main power drains of a normal computer are

  • the cpu
  • the gpu

Just to give you an example a desktop Intel I7 can reach 130W (9XX serie) while the same kind of cpu but designed for mobile I7 820QM just uses 45W.

Of course more processing power usually means more power drain at the same technology level. So you should always take into account the productive process (for I7 it's 45 nm) and the FSB used. Think about the fact that an old P4 3.0ghz with HyperThreading used 150W and had really low flops compared to today's CPUs..

About GPU think about that integrated chips (like Intel GMA serie or similar low-power chips) just drain some tenths of watts while really powerful boards can reach 160-180W when working under full load.

The third kind of CPUs used for netbooks like the Atom CPUs are able to work with just 2-6 watts of power..

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In general, laptops tend to use less power than desktops...

Unless you compare things like the latest gaming laptop against the newest power efficient desktop.

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Here is some data on the relative power usage of different PC models

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