Power

Closely related to battery life is the topic of system power draw. After all, a system that requires more power to run will typically provide less battery life. We used a Kill-A-Watt device with the batteries removed in order to record system power requirements. We also tested with minimum and maximum display brightness to show how that particular setting affects power draw, except on the maximum load where we used the brightest display setting. Please note that these are most definitely not equivalent configurations: the ASUS has a larger LCD, faster GPU, and a larger 7200 RPM hard drive, all of which should increase power use. Here are the results.

System Power Draw (Watts)
Boo! Scared you! Idle 100% CPU Maximum
ASUS A8JS 26-32 47-52 71
MSI TL-50 2x512MB 17-21 43-48 58
MSI TL-50 2x1024MB 17-22 45-50 61
MSI TL-60 2x1024MB 19-24 50-56 66

The MSI configuration with the slower TL-50 processor clearly consumes the least power. However, what's interesting is when we get to the "equivalent" configurations. The ASUS laptop still has a faster graphics processor, but what's particularly interesting is that it's the idle power consumption that really seems to affect battery life of the ASUS laptop the most. When the CPU is under full load, the ASUS system actually uses less power than the TL-60 MSI configuration. Adding graphics work to the CPU load results in the ASUS using slightly more power, but considering the higher performance it offers the extra 5W is a reasonable sacrifice. The problem comes in idle power draw, where the ASUS laptop consumes 7-8W more power than the MSI TL-60.

This leads us to an interesting conclusion in regards to battery life and power requirements. First, at maximum load the GeForce Go 7700 really doesn't apprear too bad, all told. At idle, the GPU seems to hurt the ASUS in power draw, although it could also be that the Core 2 Duo chip isn't dropping to as low a power state relative to the Turion X2. The likely explanation has to do with the old topic of AMD's integrated memory controller, along with CPU clock speeds. Both the Core 2 Duo and Turion X2 regulate processor speed by changing the CPU multiplier, but the final result is different.

First, the Turion X2 has a lower minimum multiplier of 4X with a HyperTransport bus speed of 200 MHz, resulting in a CPU speed of 800 MHz. That might seem like a relatively slow processor these days, but if your system is just sitting idle you don't need a lot of unused clock cycles. In contrast, Core 2 Duo has a minimum multiplier of 6X with a bus speed of 166 MHz, resulting in a minimum clock speed of 1000 MHz. Right there, Core 2 Duo is running 25% faster (proportionately) in its lowest sleep state.

Going back to the integrated memory controller, AMD also reduces your memory performance along with the slower CPU speed in order to further conserve power. AMD bases your memory speed off of the CPU speed, and in the case of the TL-60 using DDR2-533, at maximum CPU speed the memory is running at CPU/8 or DDR2-500. When the CPU goes into sleep state, the memory divider is also modified. In the sleep state, the memory runs at CPU/5 or DDR2-320. Memory and CPU voltages are also reduced, so the net result is that AMD is able to use less power when the system is in an idle state.

Does that make the Core 2 Duo worse at power saving than Turion X2? Without equivalent setups (i.e. both using IGP or both using discrete GPUs), we can't say for certain. We can say that an ASUS W5F with a T2300 chip (1.67GHz 2MB cache) that we had at one point bottomed out at 19W in idle mode, so Core Duo and Turion X2 appear close in low power states, with Turion X2 perhaps holding a slight 1-2W advantage. Our testing of Core Duo vs. Core 2 Duo showed the CPUs to be nearly equal in power draw, so it appears AMD is equal or slightly better than Intel at minimum power draw. At maximum power draw by the CPU, Turion X2 is definitely using more power than Core 2 Duo, as even with higher performance/power components the ASUS A8JS still uses less power than the MSI TL-60 at 100% CPU load.

Temperatures

So with the information on power requirements and performance, some of you are probably wondering how hot these systems get. Are they truly "laptops", or would they be more at home on the top of a desk or table instead? We checked temperatures over the surfaces of both systems in their maximum configurations at full load. The systems were placed on a flat, hard table surface with an ambient temperature of 23°C.

System Temperatures (Celcius)
Trick or treat? Palm Rest Keyboard Bottom Exhaust
ASUS A8JS 25-32 31-36 25-39 46
MSI TL-60 2x1024MB 27-31 31-38 29-41 48

There are several factors at play here. First, from the power requirements we know that the ASUS laptop is only consuming slightly more power. This is counteracted by the fact that it has a larger surface area, resulting in overall lower temperatures. We didn't tear apart the ASUS system in this article, but the cooling configuration is also slightly different, and there are more vents on the bottom of the ASUS A8JS. Both systems remained quiet during use even under maximum load (right around 30 dB, which is the limit of our SPL meter), but the ASUS was slightly (< 2 dB) louder during gaming sessions where the GPU and CPU are both active. More fan noise means more cooling power, which can also account for the lower temperatures on the ASUS system.

The surfaces of both laptops range from just slightly higher than room temperature up to moderately warm. Neither gets extremely hot, and most people would be okay with placing these systems on your legs, even with direct skin contact (don't mind the sweat). The only real problem we have with using either system on your lap is that this would tend to block the system fan intake, which could lead to higher temperatures and possibly even stability problems. We did use both systems in less ideal situations where the fan intake was at least partially obstructed, however, and didn't encounter and issues.

Battery Life A Quick Look at Gaming/Graphics Performance
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  • JarredWalton - Tuesday, October 17, 2006 - link

    I don't have it any more, but it was a 1.66 GHz Core Duo with 512MB RAM and IGP and an 80GB 5400 RPM HDD I believe. So at that speed it was still using aroung 18-19W at idle with minimum display brightness. I'm trying to get the owner of that laptop to run some power tests for me (our old Kristopher Kubicki has one now). Reply

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