A Custom Form Factor PCIe SSD

In the old days, increasing maximum bandwidth supported by your PATA/SATA interface was always ceremonial at first. Hard drives were rarely quick enough to need more than they were given to begin with, and only after generations of platter density increases would you see transfer rate barriers broken. Then came SSDs.

Not only do solid state drives offer amazingly low access latency, but you can hit amazingly high bandwidth figures by striping accesses across multiple NAND Flash die. A 256GB SSD can be made up of 32 independent NAND die, clustered into 8 discrete packages. A good controller will be able to have reads/writes in flight to over half of those die in parallel. The result is a setup that can quickly exceed the maximum bandwidth that SATA can offer. Today that number is roughly 500MB/s for 6Gbps SATA, which even value consumer SSDs are able to hit without trying too hard. Rather than wait for another rev of the SATA spec, SSD controller makers started eyeing native PCIe based controllers as an alternative.

You can view a traditional SSD controller as having two sides: one that talks to the array of NAND flash, and one that talks to the host system’s SATA controller. The SATA side has been limiting max sequential transfers for a while now at roughly 550MB/s. The SATA interface will talk to the host’s SATA interface, which inevitably sits on a PCIe bus. You can remove the middle man by sticking a native PCIe controller on the SSD controller. With SATA out of the way, you can now easily scale bandwidth by simply adding PCIe lanes. The first generation of consumer PCIe SSDs will use PCIe 2.0, since that’s what’s abundant/inexpensive and power efficient on modern platforms. Each PCIe lane is good for 500MB/s, bidirectional (1GB/s total). Apple’s implementation uses two PCIe 2.0 lanes, for a total of 1GB/s of bandwidth in each direction (2GB/s aggregate).

The move to a PCIe 2.0 x2 interface completely eliminates the host side bottleneck. As I pointed out in my initial look at the new MacBook Air, my review sample’s 256GB SSD had no problems delivering almost 800MB/s in peak sequential reads/writes. Do keep in mind that you’ll likely see slower results on the 128GB drive.

Users have spotted both Samsung and SanDisk based PCIe SSDs in the 2013 MacBook Airs. Thankfully Apple doesn’t occlude the controller maker too much in its drive names. An SM prefix denotes Samsung:

My review sample featured a Samsung controller. There’s very little I know about the new Samsung controller, other than it is a native PCIe solution that still leverages AHCI (this isn't NVMe). Within days of Apple launching the new MBAs, Samsung announced its first consumer PCIe SSD controller: the XP941. I can only assume the XP941 is at least somewhat related to what’s in the new MBA.

The Samsung controller is paired with a 512MB DDR3 DRAM and 8 Samsung 10nm-class (10nm - 20nm process node) MLC NAND devices. 

New PCIe SSD (top) vs. 2012 MBA SATA SSD (bottom) - Courtesy iFixit

Despite moving to PCIe, Apple continues to use its own proprietary form factor and interface for the SSD. This isn’t an M.2 drive. The M.2 spec wasn’t far enough along in time for Apple to use it this generation unfortunately. The overall drive is smaller than the previous design, partially enabled by Samsung’s smaller NAND packages.

Absolutely Insane Battery Life PCIe SSD Performance
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  • ananduser - Monday, June 24, 2013 - link

    I believe this is the first time a company has actually released a slower product than the previous gen. On principle at least Apple should be penalized in the review.

    Anand may I suggest a battery testing feature ? Count the time it takes to finish one iteration of the looping test. Maybe the battery lasts longer on a certain device but it may also take longer to finish the task. After that "normalize" the results to really measure the improvement.
  • Paapaa125 - Monday, June 24, 2013 - link

    MBA 2013-mid is not really that much slower. It has a lot faster SSD, it has a lot faster WLAN. CPU equal or slower than previous and GPU is faster than previous models. For most usages the net result is a equally fast if not faster computer. Mostly because SSD.
  • captainBOB - Tuesday, June 25, 2013 - link

    Instead of going the typical route and using all the extra power savings to increase performance while maintaining the same battery life of last year's model, Apple decided to increase battery life while maintaining performance with last year's model. Its an ultraportable.

    If you want more juice, get a Macbook Pro, the Macbook Air is all about the ultraportability.

    As for the lack of 1080p, on all those other ultrabooks with a 1080p screen, the DPI scaling is upped to 150% by default because people were complaining that text on the screen was too small, Windows still can't handle DPI scaling very well, and I doubt Windows 8.1 will change things because it will most likely be an API and still be up to the developer to update their programs to support higher resolutions. Given the "stellar" track record of the Windows desktop development community and Microsoft itself in actually USING the awesome new APIs that Microsoft creates. The situation isn't going to change the moment 8.1 comes out, it may not change for several years.

    Retina may be in the Air's future, but for now the Retina display is what clearly separates the Pro from the Air.

    If there is one criticism that is valid, its that the display should've been at least IPS.
  • ananduser - Tuesday, June 25, 2013 - link

    Spare me the marketing talk please...I never mentioned anything about the screen. Why do you feel the need to explain me Apple's motives for that ?

    They could have very well provided a 9 hour machine with a tangible increase in performance, but hey, Apple fans don't care, everything is perfect in camp Cupertino.

    PS: Since you brought it up, the Windows desktop development community is pretty stellar indeed; it's why the best software on the planet, from virtually all categories you wish to name, is made to run on Windows first and foremost. Windows(the software) always handled scaling very well, and having options like 125% or 150% is pretty nifty. Since the display pissing contest just started it will take some time until devs start to obey proper guidelines.
  • Paapaa125 - Tuesday, June 25, 2013 - link

    It's always a tradeoff. Apple went now for maximal battery life with acceptable performance. Most likely they'll focus on performance with rMBP. Sounds logical to me. I think there are many users to whom MBA has enough CPU power and they really need all day battery life. MBA now barely delivers that. Lower battery life would've meant that it will not last all day.
  • ananduser - Wednesday, June 26, 2013 - link

    So...we Anandtech readers... we who are the most pretentious of most users... can't we provide criticism ?
  • jmmx - Monday, June 24, 2013 - link

    What would like to know is this...

    I assume that turbo boost speeds will more likely occur when the unit is plugged in - i.e. it will not be draining the battery. Do any of these tests take this into account? (or did I jut not read far enough yet?)
  • Laststop311 - Monday, June 24, 2013 - link

    I totally despise apple and yes it looks like they are making a lot of mistakes with the 2013 refresh. Staying with low res screens and lower clocked processors that are actually a nudge slower than in 2012. But with the the lower clock speeds and massive battery life improvements of the haswells the macbook air is poised to be the longest running ultrabook on battery this year, especially with the larger battery that adds no weight.

    When you combine the fact that this is haswell, they stayed with low res screens added a larger battery and lowered the cpu frequencies we are in for a real treat with an ultrabook with an insane battery runtime that still has enough power to do everything an ultrabook is used for 99% of the time and do it it with performance in the mid the to midhigh pack with Top battery scores. Not to mention the thermals are probably so much cooler on this air. If Apple left it at 50% would would or probably seen 15 hour idle numbers from apple. And once OSx integrates the power management optimizer feature from haswell those battery life numbers will only go up. Eve more.

    I hate apple. But if battery life i you're #1 concern and want to routinely pull 10 hour workdays from your machine without charging the macbook air 13 model 2013 is the ultrabook for you.
  • KPOM - Thursday, June 27, 2013 - link

    All notebooks are about design compromises. Apparently Apple decided to tweak this one for battery life rather than use Haswell as an opportunity to put in a faster processor or better screen. Hopefully they'll find a way to shave a few ounces off the weight of the 13" rMBP. I have one and like it, but miss the portability of the Air.
  • Laststop311 - Monday, June 24, 2013 - link

    I wish sata would just completely die off and intel increased in PCI lines by double 80X on enterprise 32x on consumer and have all new HDD and SSD connect via PCI 3.0 1GB/SEC bi directional. Can just use 1x lanes for all the storage devices maybe a few 2x lane connections for super high performance ssd;s. But probably won't see this wish till 2GB/sec bi directional pcie-e 4.0. Where we can easily stack up 8 SSD's on 1s lanes while still providing enough lanes for full GPU use. I hope pci 4.0 brings the full death of sata and its outdated ways. Even if we have to call it sata express. The Use of SATA needs to be fully dead by pci-e 4.0. Yea that includes even having to run a practically obsolete blu ray burners off a 1x line but who knows by then there may be a disc much puerior yo blu ray that can actually use the extra bandwidth. Would simplify computers no longer having to have all that data hardware on there too.

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