NAND Performance

The $199 Nexus 7 ships with 8GB of NAND on-board in the form of a standalone eMMC 4.41 package from Kingston. The single package storage solution features NAND and controller, although as you can guess there's no room for DRAM. The NAND in use is MLC although it's not clear whether we're looking at 2 or 3-bits per cell. This basic architecture shouldn't be all that unfamiliar to long time AnandTech readers - the cacheless design is exactly what plagued some of the early MLC SSDs for PCs a few years ago.

More recently users have been noticing very poor performance with ASUS Android tablets whenever there's substantial background IO going on, particularly multitasking while writes are taking place (e.g. downloading a torrent and browsing the web). The slowdowns range from multi-second long pauses to sluggish response time. The video below shows you what can happen on a Transformer Pad Infinity while downloading a bunch of large files in the background:

Even though downloading a large file is a largely sequential write operation, any other action performed while that download is in progress will effectively turn the IO stream from purely sequential to pseudo-random. Most of these eMMC and other cheap MLC NAND flash controllers are really glorified SD cards, primarily optimized for reading and writing large images as if they were used in a camera. What they're not designed for is to run and be used in a full blown multitasking OS. Some manufacturers seem to do a better job of picking their storage solution, and the Kingston eMMC in the Nexus 7 is faster than the Hynix e-NAND ASUS has used in previous tablets. Neither is perfect however. There's a tangible impact on simple multitasking if you're downloading a lot of files or installing apps in the background. Even operations in memory are quite negatively affected by background IO. Take a look at how SunSpider performance is hurt by a background file download:

SunSpider 9.1 Performance
  Default With 2MB/s Background Download
Google Nexus 7 (8GB) 1665.9 ms 1984.9 ms

To put all of this in perspective, I turned to Androbench, a storage benchmark that allows an ok amount of flexibility in configuring the test environment. At its default settings the benchmark varies a bit too much for my liking, but if you up the buffer sizes to 100MB it helps smooth out some of the variance.

Here we're looking at both sequential and random IO, the two sides we pay attention to in our SSD reviews as well. It's not clear to me whether or not Androbench is clamping the random IO to a particular range of addresses or not, but the results are telling nonetheless:

Androbench (100MB read/write)
  256KB Sequential Read 256KB Sequential Write 4KB Random Read 4KB Random Write
ASUS Transformer Pad Infinity (64GB) 15.9 MB/s 7.13 MB/s 4.90 MB/s 0.22 MB/s
Google Nexus 7 (8GB) 23.1 MB/s 8.43 MB/s 4.77 MB/s 0.32 MB/s
Samsung Galaxy Nexus (16GB) 26.8 MB/s 7.29 MB/s 7.46 MB/s 0.23 MB/s

Sequential read/write speed isn't bad, but it's the random write speed that's really a problem. We're talking about write speeds of a couple hundred KB/s. Remember what I said earlier about how multitasking can take an otherwise sequential IO stream and make it look fairly random? I suspect the low random write performance is one reason we're seeing significant slowdowns with background IO. Not all NAND controllers do well with concurrent reads and writes, which could be another contributing factor to poor performance.

Note that for light usage this isn't a problem. Similar to the first generation of affordable MLC SSDs for PCs, as long as you're doing a lot of reading you'll be ok. It's really for the heavier usage models that this is a problem. On a tablet however, simple background installation or downloading of files counts as heavy these days.

The real solution to this problem is to integrate better NAND flash controllers on-board, or even onto the SoC itself. Tablet makers are still mostly focused on cost cutting, but eventually we'll see real SSDs with good controllers in these things. Windows 8 tablets, at least the high end ones due out later this year will be among the first to incorporate real SSDs.

WiFi Performance, NFC

The Nexus 7 includes support for single spatial stream 802.11b/g/n on 2.4 GHz only. That ends up being a PHY rate of 65 Mbps (single spatial stream with no SGI). ASUS has been using AzureWave modules for basically every single one of its tablets, and the Nexus 7 is no exception. Thanks to the FCC test reports, you can see an AW-NH665 module alongside the new NXP PN65 NFC controller. The AW-NH665 includes a BCM4330 inside - remember there are different vendors who will sell you a completed module.


NXP PN65 NFC, AzureWave AW-NH665 (Source: FCC Internal Photos)

If you're looking for a cost cutting measure, the lack of 5 GHz WLAN support is most definitely one. In fact, the lack of 5 GHz WLAN made for probably one of my most memorably hilarious Google I/O experiences, since the event had multiple signs noting that only devices with 5 GHz WLAN would work well (or at all - 2.4 GHz is unuseable at any major event) on the conference WiFi. To mitigate this, Google hooked up USB OTG to MacBook Air ethernet adapters for its Nexus 7 demo stands, which I of course hijacked for my Galaxy Nexus at one point. More and more, having 5 GHz WLAN in a tablet is an expectation, and soon we'll even start seeing 2x2:2 antenna configurations.

The resulting performance is pretty par for the course when it comes to WiFi speeds among single spatial stream 2.4 GHz only devices. I tested using iperf the same way I do smartphones. 

WiFi Performance - iPerf

Unlike some of the other ASUS tablets of note, there are no reception issues with the Nexus 7 either. I have no problem getting good reception and see the Nexus 7 fall off the network where I expect it to in my area. I think it's worth being explicit about where the antennas are located since wireless connectivity issues have been a recurring issue for just about every product. 


BT/WLAN (red), NFC (blue), GPS (green)

I've gone ahead and marked where the antennas are for BT/WLAN, NFC, and GPS on the case from the FCC teardown photos. Knowing exactly where the NFC coil antenna is located is actually hugely important for correctly positioning the device for beaming or reading tags. It ends up being right behind the "nexus" recessed lettering on the back, but until I saw the antenna in the FCC teardowns I wasn't completely sure. With a smartphone the size makes it relatively forgiving, but tablets are less forgiving about positioning not being exact thanks to the larger size. 

GPS

The Nexus 7 uses a monolithic Broadcom BCM4751 GPS receiver, which we've seen in other devices like the iPad 2. This isn't the absolute newest broadcom GPS/GNSS, and again I'm sure ASUS was able to secure great pricing for this since the newer GNSS (GPS+GLONASS) modules are making their way into devices right now. 

That said, I had no problems with GPS locking quickly from cold and warm starts. I walked around San Francisco with the Nexus 7 using Google Maps (tethered to an SGS3) and saw pretty good performance in the urban canyon scenario. With no occlusions to the sky, performance is excellent, and locks indoors are possible too. 

 

GPU Performance Battery Life
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  • bennyg - Tuesday, July 31, 2012 - link

    Maybe Google saw the gobs of cash Apple make from crazy high markups on storage once you lock your userbase out of choice in the matter.

    I'm glad Android has internal competition in the smartphone area for this reason. Time will tell if my decision to opt for 8gb is a bad one, but really since it has no camera I'll only ever run out of space when copying something onto it which puts me firmly in control and I'm fine with that.
    Reply
  • fmcjw - Thursday, August 02, 2012 - link

    Applaud mentioning that Google is charging $50 for $4 of NAND. Wondering why Apple is not reviewed with such analytic words.

    Brian's and Anand's writing are the only knowledgeable content on this site, with the rest being filler material. That said, still not lowering my ad-block on Anandtech, since Anand drools praise on Apple products, throwing money at a 117b dollar rich company which is:
    monopolistic (in behavior if not absolute terms),
    dictatorial (imposing business-driven restrictions on technology), and
    unimaginative (riding wave of state of the art tech manufacturing, always at the cusp of killing established business models with many players for its sole profit)

    IMO Anand is single minded and is narrow in his views. Yes, he appreciates "the best" tech, but is eager to distance himself from less obvious virtues and legacy concerns. It's also apparent he feels no responsibility and vision towards diversity, choice, and the underdogs in the industry, preferring the elite wherever possible, Intel over AMD, Apple over the rest. By being "objective" and focused on what he deems palatable and suitable, he is no different from Monsanto: technology in a vacuum, umbilical cord as leash.

    And once he is happily on Apple's leash, you can see how his values get whipped around.
    Reply
  • NoNeedForMonkeys - Saturday, August 04, 2012 - link

    I have not had to pay for cloud storage. The N7 is a play store front-end for media streaming. Google is heavily pushing streaming services over local storage.

    The USB port on this thing is compliant to MHL specs and future software should be able to enable HDMI adapters, but the software is not allowing full functionality yet. The USB port is also hardware compliant with USB OTG, it is just not enabled in software.
    Reply
  • EnzoFX - Thursday, July 26, 2012 - link

    What is there for a reviewer to talk about besides simply stating it doesn't have one? Which they all do. It doesn't have one, this you know already, you're either ok with it, or it's not for you. They know what they did and they still chose to do it. Get over it? Reply
  • Sined - Thursday, July 26, 2012 - link

    To be honest, it's a bit unfair to knock on any Android Device for the lack of MicroSD card storage.

    Dan Morrill of Google's Android Team explains why:
    http://www.androidpolice.com/2011/11/18/impromptu-...

    It has to do with how USB Mass Storage works and how Apps and Media mingle in the same storage when dealing with internal storage only.

    Ideally, ALL Android devices should have SD Cards but Android hasn't matured in that department enough to have them on the Nexus Line.
    Reply
  • Death666Angel - Thursday, July 26, 2012 - link

    As I read that, he says they don't have a microSD slot because it would make settings up things harder ("where does the camera save pictures, where should that app be installed?"). I am glad that I only have android devices with microSD slots. I don't agree with the dumbing down of options he wants. If I wanted that, I'd go with iOS. :-) Looks like I won't get any Nexus device any time soon. Reply
  • leexgx - Saturday, July 28, 2012 - link

    Samsung seem to do it right, the as the main 16gb mem (for example) is split norm 2gb and 12gb (that shows as an SD card)

    and ones with an SD card slot are shown as an second SD card slot
    Reply
  • robinthakur - Tuesday, July 31, 2012 - link

    Yes, a shame that the phone slows down so much when you start filling up the internal memory though, its like it doesn't ring-fence enough for the OS. Reply
  • Impulses - Friday, July 27, 2012 - link

    Yeah, I don't think they've omitted the expandable storage slots for any one particular reason but more a combination of them... Usability + cost cutting + working out some technical aspects. Still, it's a compromise and he admits as much.

    I think the best compromise is what HTC did with the EVO LTE and what I believe Samsung did with the SGS3: internal storage is all MTP so apps, media, and the OS can share the space without strict partitions and you don't need to unmount from theOS to sync content, and the external storage is still good old UMS so you can work around MTP sync issues and/or have expandable storage for media.

    It's still a compromise tho, what Morrill states is true, not all apps are built to scan external storage or handle the disconnect of it elegantly. The OS handles it just fine in the case of music/photos IMO (since there's a media scanner) but other stuff can be hit or miss.
    Reply
  • Shadowmaster625 - Thursday, July 26, 2012 - link

    Anyone who buys a device like this with no storage option is just a fool. Let it burn. Reply

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