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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  • Sprchkn - Thursday, July 26, 2012 - link

    Except that Flash isn't supported on Jelly Bean... I know, mine arrived yesterday and I tried that. Amazon either needs to release an Android app or move to HTML5.

    But, I've already cancelled the auto-renewal on my Prime account due to their use of Flash DRM which requires a workaround to install the deprecated HAL package under Gentoo so it's not like I'm married to them. Google actually seems to be the only one that supports both Linux and Android, so I'll just start purchasing my video content from them.
    Reply
  • Impulses - Friday, July 27, 2012 - link

    Flash works fine on Jelly Bean under Firefox and other browsers, just need to side load it. Reply
  • RamarC - Thursday, July 26, 2012 - link

    will allow usb tthumb drive/sd cards to be used with the Nexus 7. Reply
  • WolvenSpectre - Thursday, November 08, 2012 - link

    The problem is that it doesn't give you any write capability. Reply
  • Pino - Thursday, July 26, 2012 - link

    "213 pixels per inch in a 7 inch display is unique for an Android tablet"

    Lenovo´s S2007 tablet has such a display and was launched way before the Nexus 7:

    http://appserver.lenovo.com.cn/Lenovo_lepadSeries_...
    Reply
  • eaanders@cox.net - Thursday, July 26, 2012 - link

    The primary advantage of the Nexus 7 is price. If a tablet is so small you need to zoom, the sweet spot is the Galaxy Note. It's half the weight of the 7, fits in your shirt pocket, and combines the features of a phone, a camera, and a small tablet in one unit with the possibility of adding an additional 32 Gb of storage. The Note 2 will be even faster.

    My netbook will be replaced by a Windows 8 hybrid eventually for full computing power. This and the Galaxy Note are all I will need to do everything mobile.
    Reply
  • Sprchkn - Thursday, July 26, 2012 - link

    I think it depends on what you're using it for. I bought the Nexus 7 so that I can leave my phone docked up to my stereo and then look up recipes, check email, etc. while I'm in the kitchen cooking. The speakers are a bit weak, but it will probably also see some duty playing movies, again, while I'm cooking or perhaps when I'm on my treadmill. The missing storage hasn't been a problem for me with the way I use my phone and I always have my iPod available for music duty. Besides, for whatever reason, I've always had trouble with the micro SDs and corruption when copying large amounts of data onto them - so I'm actually relieved that Google Play means I no longer have to deal with that. Reply
  • MadMan007 - Thursday, July 26, 2012 - link

    An unlocked Galaxy Note is over twice as expensive as the Nexus 7. It's only fair to compare unsubsidized vs unsubsidized pricing. Everyone's needs and wants are different, but the 'if you're going to zoom anyway' point is valid if one were going to get a subsidized phone anyway and can deal with the size of the Note as a phone. Reply
  • hackbod - Thursday, July 26, 2012 - link

    Great stuff on the NAND performance, as well as the commentary on the screen configuration. Your reviews are consistently the most detailed and technically accurate I see.

    One thing that would be interesting to do is NAND performance comparisons with the 16GB model. I believe this uses a different NAND controller, so you should see some different interesting behavior. And since the 16GB model is likely more popular than the 8GB one, this would be relevant to many people.
    Reply
  • risa2000 - Friday, July 27, 2012 - link

    I would like to see similar tests (flash throughput) done also with smartphones. There has been rumors that there are some significant difference between some (e.g. iPhone and some Androids) and it would be interesting to know also for new WP devices. Reply

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