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If I want to maximize the battery life on my laptop, where should I store my programs: my magnetic hard drive or my 16GB SD card?

  • If you say hard drive, does a card reader draw significantly more power when a card is inserted (but not accessing it) vs. left empty?

  • If you say sd card, are there significant power consumption differences between SD cards, Memory sticks, micro, mini, xD, etc? (My laptop has a multi-card reader and I should pick the most energy-efficient kind.)

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4 Answers 4

up vote 4 down vote accepted

Short answer: Programs should go on Hard Drives not SD cards even though the SD card pulls significantly less power. A majority of power is used by an SD card reader is used to power the SD card itself.

Explanation:

Simply having a hard drive plugged in can pull anywhere from 6-10 watts. When reading data, an additional 3-5 watts are used. SD cards use about 1 watt at max load and are much slower than a normal hard drive. The performance hit you are going to take by putting your programs on the SD card is not really worth the power savings of 2-4 watts. That of course assumes that the hard drive remains idle while the program runs. If anything accesses the hard drive, the power saving is lost since the drive has to spin up to fetch the data.

The better way to lower your power consumption is to switch a spinning disk (6-10 Watts) to an SSD (2 Watts). This reduced the power load but doesn't sacrifice performance.

But you don't have to take my word for it, you can test this yourself. All you need is a power monitor like a Kill-A-Watt. Use the Kill-A-Watt like a power strip and run your laptop off of AC power. Capture the amount of power used in each scenario over the course of at least an hour. The lower number wins the test.

[EDIT]

I did some digging and found two interesting sources:

MSDN Blog entry on power consumption - This page shows the power usage breakdown by component. Written in 2009, it shows that a hard drive takes up about 5% of the total load of a system. That math puts hard drive consumption at 1.5W at 30W load and 4.5W at a 90W load. Knowing what we know about hard drive, that is a very generous number that probably takes an average of power usage over multiple idle events. The cart is still good to understand the general power consumption.

uiuc.edu research paper hosted at PSU - This PDF document has a component by component breakdown of power consumption. This is working with an old Pentium M, but it backups up the ratios of power draw. The hard drive is a minor part of total power consumption. This ranged from 3% to 15% of total power depending on what was going on. That 15% only happened when the system was doing a hard drive stress test. The total wattage at this high percentage was still only 3W out of 18W total draw.

So what does this mean? That trying to idle your system will only save on average only 5% of your total power draw. Even though you are technically right when it comes to power usage, it will slow down you machine and the power savings is minor.

[End EDIT]

Hope this helps

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Class 10 SD cards beat hard drives in read and seek times, right? That's why ReadyBoost was invented. Going by what you're saying, if I can somehow keep the drive idle and low power while the program runs (e.g., no pagefile, ram disks), then programs ought to go to the SD card. What do you think? –  William C May 13 '11 at 23:46
1  
In seek times, a hard drive can't compete with flash chips. But that advantage is nothing when compared to raw throughput. A Class 10 SD card is at the speed hard drives were in the 90's. Nowadays, a Hard drive is anywhere from 4-10 times faster. You should test your own drive to see what the max throughput (read/write) speeds are. hdtune.com is a good tool to test this. After looking at the numbers you can figure out what is best. –  Doltknuckle May 16 '11 at 15:12

Wikipedia's article about Secure Digital (SD) says this :

The power consumption of microSD cards varies by manufacturer, but appears to be in the range of 66-330 mW (20-100 mA at a supply voltage of 3.3 V). Specifications from TwinMos technologies list a maximum of 149 mW (45 mA) during transfer.[21] Toshiba, on the other hand, lists 264-330 mW (80-100 mA).

In the article Hard Disk Drive Power Consumption Measurements: X-bit’s Methodology Indepth the consumption of a hard disk was very carefully measured to be :

the multimeter reported the following: 1.06A average consumption, 1.13A maximum consumption. The oscilloscope data reads: 1.04A average consumption and 2.71A maximum consumption. As you can see, the multimeter managed to get the average value pretty closely, but failed to catch any of the consumption peaks.

Any hard disk review will normally claim between 6-10 W, which is an order of magnitude more consumption than the SD card.

Regarding SSD, there is a surprise in the artice SSD hard drives tank laptop battery life which shows that :

not only are they not as energy efficient, SSDs actually use more power than conventional hard drives.

That said, although SD cards are much more energy efficient, it is not recommended to use them as hard disks. SD cards are much more prone to failure than hard disks, and should really be used with great caution. Their performance also is quite abysmal.

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-1 for just dumping Google search results. While the SD information is good, the hard drive information misses the point. Power consumption is based off of Watts, which is derived by both amps and volts. A Hard disk will pull anywhere from 6 to 10 Watts not Amps like you stated. What really gives you the -1 is the SSD article from 2008 dealing with 32GB SSD drives. That article is so out of date that it is irrelevant to the discussion. You need to realize that SSD's have been around since the 1970's but only recently have advanced to take the place of hard drives. –  Doltknuckle May 11 '11 at 19:58
    
tomshardware.com/reviews/windows-7-ssd-trim,2705-19.html <- this 2010 article gives you a much better idea of what current day SSD power consumption is. An Intel 25-M is between .1 Watts and 1.4 Watts. –  Doltknuckle May 11 '11 at 20:01
    
Looking back over the Hard Disk article I notice that it is about the difference between using a multimeter and oscilloscope for measuring power consumption. While the information is still relevant, the article is dated 2007. The new western digital green drives idle at 5.5 watts and are rated 6 Watts under load. The advice is still good though. –  Doltknuckle May 11 '11 at 20:12
    
@Doltknuckle - " You need to realize that SSD's have been around since the 1970's" - Citation please. Core memory was still in wide-spread use in the 1970s. DRAM would be impractical for a storage device, as VLSI was still an emerging technology. Battery-backed SRAM could be the viable, but very expensive and bulky. –  sawdust Nov 19 '12 at 2:30
    
@sawdust en.wikipedia.org/wiki/Solid-state_drive - Anything that uses integrated circuits is a solid state drive. In the 70's it was highly impractical for most storage scenarios. This technology has evolved over the last few years and if you look at the specs of an SSD sold today, it is a different story than an SSD available in 2008. Which was the year the comparison was made between a magnetic hard drive and an SSD. –  Doltknuckle Jan 10 '13 at 17:39

You may want to take a look at the reviews on StorageReview.com. These include power consumption numbers near the end of each review.

Unfortunately I don't think I have every seen a SD card reader on there, but it may still help you find a low draw device, and to get a feeling for the behavior of SSD / HDD power consumption.

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someone has been misinformed. SSD's use 1/10th the power of a traditional HD and do not put out the heat that a regular drive does. Remember, the laptop has to remove that extra heat at some point and therefore uses more power to do so. This was not factored into the load test/overall power consumption.

SSd are fast and therefore you can get more done faster. If you get done faster than you can shut down earlier and save energy that way.

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1  
SD card, not SSD. :) –  Ƭᴇcʜιᴇ007 Nov 20 '12 at 4:57

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