The Impact of SSD on Battery Life

One advantage of solid state storage is lower power consumption thanks to not having any motors or moving heads to drive; spinning anything 4200 times a minute is going to be more power hungry than a solid state solution. The SSD vs. mechanical HDD power debate would normally be a clear cut one but we're comparing to one of the lowest power HDDs on the market here.


Power Consumption 80GB 4200RPM HDD 64GB SSD
Read/Write 0.9W 0.24W/0.36W
Idle 0.30W 0.035W
Standby 0.07W 0.035W
Sleep N/A 0.015W


The power savings are dramatic; idle power is reduced by nearly a factor of 10, standby power is cut in half and read/write power is at worst a third of the mechanical drive. The 10x idle power reduction is important since that's where your drive should be spending most of its time, and if the average power savings is somewhere in the 0.25 - 0.5W range you're looking at improving battery life on the order of tens of minutes.

To find out the impact on battery life we ran through three different scenarios:

I scripted together three tests: wireless web browsing, DVD playback and a multitasking workload.

The wireless web browsing test uses the 802.11n connection to browse a series of 20 web pages varying in size, spending 20 seconds on each page (I timed how long it takes me to read a page on Digg and came up with 36 seconds; I standardized on 20 seconds for the test to make things a little more stressful). The test continues to loop all while playing MP3s in iTunes. This test is designed to simulate the intended usage of the MacBook Air: something you can carry around with you to class, work, on the train, etc... to comfortably and quickly browse the web, take notes and generally be productive all while listening to music. It's like a big iPhone...without the phone part.

Despite the lack of an internal optical drive (I've never been so tempted to use the f-bomb in a review before), the MacBook Air will play DVDs. You just kind of need to have them on your hard drive and I'll just assume you have the original disc safe at home. This test is simple: I play Blood Diamond in a loop until the battery runs out.

The final test is the multitasking workload, and this test isn't really that intensive for a normal system but thanks to the terribly slow iPod hard drive in the Air - it's quite stressful. For this benchmark I'm downloading 10GB worth of files from the net (constant writes to the drive), browsing the web (same test as the first one) and watching the first two episodes of Firefly encoded in a 480p XviD format (Quicktime is set to loop the content until the system dies). There's nothing too extreme about this workload, I could definitely come up with worse - but this would be light to moderate usage on a MacBook or a MacBook Pro, and it'll show how the Air stacks up.

The system was set to never shut off the display and never go to sleep, although the hard drive was allowed to spin down when possible. The display brightness was set at 9 blocks (just over 50%), which I felt was comfortable for both day and night viewing.


Battery Life Test (H:MM) 80GB 4200RPM HDD 64GB SSD % Improvement
Wireless Internet + MP3 4:16 4:59 16.8%
DVD Playback 3:25 3:56 15.1%
Heavy Downloading + XviD + Web Browsing 2:26 2:42 11.0%


As expected, the impact on battery life isn't huge but it's definitely noticeable. With the 64GB SSD installed we're actually able to hit Apple's 5 hour battery life claim with the MacBook Air. Our wireless browsing test actually saw the biggest improvement in battery life, increasing a full 43 minutes from a simple drive swap.

The DVD playback test got the next largest boost of 31 minutes or 15.1%, followed by the multitasking scenario that saw a more meager 16 minute increase in battery life.

With an average increase in battery life of 30 minutes, you're paying an extra $33 per minute of battery life based on present day SSD upgrade pricing from Apple. If you look at it that way, the improvements stop being as exciting - but the takeaway point is that the technology is useful and down the road, when SSD prices drop, you can look forward to an upgrade that does improve the overall experience.

MacBook Air Performance: SSD vs. Mechanical HDD The SSD Discussion
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  • aliasfox - Thursday, February 14, 2008 - link

    It may be 50% faster than the 1.2 GHz ULV processors in most other ultraportables, but that also means it's also about 50% slower than most mainstream high end CPUs (2.2 GHz and up).

    Slow hard drive doesn't help either.
    Reply
  • sprockkets - Wednesday, February 13, 2008 - link

    I don't get it. I can use my Pioneer laptop slot loading burner on an external enclosure and it be powered solely via the one usb port and works just fine, even while writing to dvds.

    For that matter, I can do the same with notebook laptop drives. Rarely do I need both usb ports connected in order for it to work.
    Reply
  • sprockkets - Wednesday, February 13, 2008 - link

    Only about 16mbits per second on the xfer rate on wireless? Wow. Were you using n? Reply
  • JarredWalton - Thursday, February 14, 2008 - link

    I don't know what Anand used, but I've seen everything from 3MBps to 12MBps on an 802.11n network... all with laptops in the same room, and many using the same chipset (Intel 4965AGN). Overall, N tends to feel about half as fast as 100Mbit Ethernet - or about twice as fast as 802.11G. Router choice unfortunately still has a major influence on 802.11N performance. Reply
  • Imaginer - Wednesday, February 13, 2008 - link

    It is what the overall feel and message of the article indicates to me. It is a bit expensive, non-expansive, lacks most utility to be used in most mobile situations, and it is purely for computing on the bare minimum.

    Kind of like that so called weekend car. I don't think I myself will have ANY need for such a device. Give me a powerful desktop and a versitle yet remaining non cumbersome notebook anyday.

    Most people in the market for a laptop usually would use it like their normal away from home computer and because of this, the air really disappoints. (not that I would invest in a new computer anytime soon).
    Reply
  • jedmitchell - Wednesday, February 13, 2008 - link

    hey, so good review overall -- kept it very even handed considering the difficulty of reviewing a niche product like this. one hardware point I'd like to mention though is the info you give on the X3100. certainly the idea behind it is that as an integrated controller it won't provide very fast graphics, but there's a trick here: most of the things it's not rated to run... run. at least on the older macBook (santa rosa). final cut pro, maya, and photoshop actually all run pretty seamlessly on the X3100, both in OSX and windows (fcp is more memory/drive limited there than GPU). the only small problems are in windows where the X3100 drivers by intel are actually lacking several openGL 2.0 features present in apple's version.

    the X3100 even plays older games on windows without much trouble -- I can run the Orange Box games at 1024x768 with high quality settings and see a fairly regular 30fps, less a few texture memory glitches. anyway, it would be interesting to see how that performance in the same chipset scales from the macBook to the air.
    Reply
  • jdwango - Wednesday, February 13, 2008 - link

    However I wish you had also tried to install Windows XP/Vista via boot camp and reported your thoughts. Reply
  • joey2264 - Wednesday, February 13, 2008 - link

    This would be a fairly good review if you would just mention the fact that most of the sacrifices Apple made to create the Macbook Air simply weren't necessary. If you look like at a notebook like the Fujitsu Lifebook S6510 of the Lenovo X300 this becomes clear. Looking at these two notebooks, it is obvious that each of the manufacturers could have come up with a 13.3 in, 1 spindle notebook that didn't make hardly any other compromises (decent keyboard, decent port selection, replaceable battery, upgradeable memory, standard 2.5" hard drives (Lenovo could have probably fit a 2.5" hard drive in there if they had used a 13.3" screen, with the requisite larger footprint, although it would have been a little heavier), etc). Reply
  • michael2k - Wednesday, February 13, 2008 - link

    The S6510 you mention is heavier (by a pound) and nearly twice as thick! It is much more comparable to a MacBook (5 pounds and an inch thick vs 4 pounds and 1.42 inches thick).

    The X300 is also not available yet, so a comparison will have to wait until we find out about price and build quality.
    Reply
  • mlambert890 - Thursday, February 14, 2008 - link

    OK, so then the Sony TX, the Fujitsu P7k, the Toshiba Portege, the Dialogue Flybook, the Panasonic Toughbook, the Dell XPS1210, the Sony SZ, The LG XNote....

    There's a pretty long list of notes that are smaller and ligher or as light or slightly heavier with a lot more features than the MBA.

    The MBA is THINNER. Last I checked thinner is a BS feature. When someone can explain to me WHY thinner means ANYTHING beyond looking cool at Starbucks, maybe Ill be interested.

    The Sony X505 was pretty much the same situation as the MBA except it had a removable battery and more ports and that was 3 years ago. I think the MBA was like .2" thinner than the Sony *at its thinnest point* and about the same at the thickest.

    The MBA is big news for the cult of Mac which lately is including PC sites like this.
    Reply

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