A Post about Removable Storage, Removable Batteries and Smartphones
by Anand Lal Shimpi & Brian Klug on November 25, 2013 8:40 PM EST- Posted in
- Smartphones
- Mobile
There's been a lot of talk lately about our position on removable storage and removable batteries in smartphones. Most of the discussion has centered around what we've said in podcasts or alluded to in reviews, so we figured it's a good time to have the complete discussion in one central location.
Let's get through the basics first:
All else being equal, removable storage and user replaceable batteries aren't inherently bad things. In fact, they can offer major benefits to end users.
The key phrase however is "all else being equal". This is where the tradeoff comes in. On the battery front, the tradeoff is very similar to what we saw happen in notebooks. The move away from removable batteries allows for better use of internal volume, which in turn increases the size of battery you can include at the same device size. There are potential build quality benefits here as well since the manufacturer doesn't need to deal with building a solid feeling removable door/back of some sort. That's not to say that unibody designs inherently feel better, it's just that they can be. The tradeoff for removable vs. integrated battery is one of battery capacity/battery life on a single charge. Would you rather have a longer lasting battery or a shorter one with the ability the swap out batteries? The bulk of the market seems to prefer the former, which is what we saw in notebooks as well (hence the transition away from removable batteries in notebooks). This isn't to say that some users don't prefer having a removable battery and are fine carrying multiple batteries, it's just that the trend has been away from that and a big part of the trend is set based on usage models observed by the manufacturers. Note that we also don't penalize manufacturers for choosing one way or another in our reviews.
The tradeoffs are simple with an internal battery, the OEM doesn't need to include a rigid support structure on the battery to prevent bending, and doesn't need to replicate complicated battery protection circuitry, and can play with alternative 3D structures (so called stacked batteries) for the battery and mainboard as well. Personally, I'd rather have something that lasts longer on a single charge and makes better use of internal volume as that offers the best form factor/battery life tradeoff (not to mention that I'm unlikely to carry a stack of charged batteries with me). It took a while for this to sink in, but Brian's recommendation to charge opportunistically finally clicked with me. I used to delay charging my smartphone battery until it dropped below a certain level and I absolutely needed to, but plugging in opportunistically is a change I've made lately that really makes a lot of sense to me now.
The argument against removable storage is a similar one. There's the question of where to put the microSD card slot, and if you stick it behind a removable door you do run into the same potential tradeoff vs. build quality and usable volume for things like an integrated battery. I suspect this is why it's so common to see microSD card slots used on devices that also have removable batteries - once you make the tradeoff, it makes sense to exploit it as much as possible.
There's more to discuss when it comes to microSD storage however. First there's the OS integration discussion. Google's official stance on this appears to be that multiple storage volumes that are user managed is confusing to the end user. It's important to note that this is an argument targeted at improving mainstream usage. Here Google (like Apple), is trying to avoid the whole C-drive vs. D-drive confusion that exists within the traditional PC market. In fact, if you pay attention, a lot of the decisions driving these new mobile platforms are motivated by a desire to correct "mistakes" or remove painpoints from the traditional PC user experience. There are of course software workarounds to combining multiple types of storage into a single volume, but you only have to look at the issues with SSD caching on the PC to see what doing so across performance boundaries can do to things. Apple and Google have all officially settled on a single storage device exposed as a single pool of storage, so anything above and beyond that requires 3rd party OEM intervention.
The physical impact as well as the lack of sanctioned OS support are what will keep microSD out of a lot of flagship devices.
In the Android space, OEMs use microSD card slots as a way to differentiate - which is one of the things that makes Android so popular globally, the ability to target across usage models. The NAND inside your smarpthone/tablet and in your microSD card is built similarly, however internal NAND should be higher endurance/more reliable as any unexpected failures here will cause a device RMA, whereas microSD card failure is a much smaller exchange. The key word here is should, as I'm sure there are tradeoffs/cost optimizations made on this front as well.
The performance discussion also can't be ignored. Remember that a single NAND die isn't particularly fast, it's the parallel access of multiple NAND die that gives us good performance. Here you're just going to be space limited in a microSD card. Internal NAND should also be better optimized for random IO performance (that should word again), although we've definitely seen a broad spectrum of implementation in Android smartphones (thankfully it is getting better). The best SoC vendors will actually integrate proper SSD/NAND controllers into their SoCs, which can provide a huge performance/endurance advantage over any external controller. Remember the early days of SSDs on the PC? The controllers that get stuffed into microSD cards, USB sticks, etc... are going to be even worse. If you're relying on microSD cards for storage, try to keep accesses to large block sequentials. Avoid filling the drive with small files and you should be ok.
I fully accept that large file, slow access storage can work on microSD cards. Things like movies or music that are streamed at a constant, and relatively low datarate are about the only things you'll want to stick on these devices (again presuming you have good backups elsewhere).
I feel like a lot of the demand for microSD support stems from the fact that internal storage capacity was viewed as a way to cost optimize the platform as well as drive margins up on upgrades. Until recently, IO performance measurement wasn't much of a thing in mobile. You'd see complaints about display, but OEMs are always looking for areas to save cost - if users aren't going to complain about the quality/size/speed of internal storage, why not sacrifice a bit there and placate by including a microSD card slot? Unfortunately the problem with that solution is the OEM is off the hook for providing the best internal storage option, and you end up with a device that just has mediocre storage across the board.
What we really need to see here are 32/64/128GB configurations, with a rational increase in price between steps. Remember high-end MLC NAND pricing is down below $0.80/GB, even if you assume a healthy margin for the OEM we're talking about ~$50 per 32GB upgrade for high-speed, high-endurance internal NAND. Sacrifice on margin a bit and the pricing can easily be $25 - $35 per 32GB upgrade.
Ultimately this is where the position comes from. MicroSD cards themselves represent a performance/endurance tradeoff, there is potentially a physical tradeoff (nerfing a unibody design, and once you go down that path you can also lose internal volume for battery use) and without Google's support we'll never see them used in flagship Nexus devices. There's nothing inherently wrong with the use of microSD as an external storage option, but by and large that ship has sailed. Manufacturers tend to make design decisions around what they believe will sell, and for many the requirement for removable storage just isn't high up on the list. Similar to our position on removable batteries, devices aren't penalized in our reviews for having/not-having a removable microSD card slot.
Once you start looking at it through the lens of a manufacturer trying to balance build quality, internal volume optimization and the need for external storage, it becomes a simpler decision to ditch the slot. Particularly on mobile devices where some sort of a cloud connection is implied, leveraging the network for mass storage makes sense. This brings up a separate discussion about mobile network operators and usage based billing, but the solution there is operator revolution.
I'm personally more interested in seeing the price of internal storage decrease, and the performance increase. We stand to gain a lot more from advocating that manufacturers move to higher capacities at lower price points and to start taking random IO performance more seriously.
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cbf - Tuesday, November 26, 2013 - link
I have to disagree with Anand on this. I have two very simple use cases:1. Quick battery swap. I always keep an extra battery in my charger. **Some nights I forget to plug my phone into the charger**. Next morning I just swap batteries. Plus, when I'm travelling, I take along the extra battery -- sometimes when out and about, spending lots of time in conference rooms, etc., my battery is dying by dinner time -- precisely when I need my phone the most.
2. ** These phones are cameras ** -- for most people their primary and most used camera (still and video!). Would you buy a camera that only had internal storage?? (And as many have pointed out, where the manufacturer charged you $100 for an extra 16Gb!?).
TheWarOnPants - Tuesday, November 26, 2013 - link
I, too, would love to see fast, cheap, abundant internal storage. But until that day happens I'm going to buy Samsung phones.BugblatterIII - Tuesday, November 26, 2013 - link
Why does a slot for a microSD card compromise the build quality but a slot for a SIM card presumably doesn't? If a unibody design can accommodate one it can accommodate the other.As for the battery, I do carry a spare. Also if the battery life starts to degrade over time I can get it back as new with a new battery.
repoman27 - Wednesday, November 27, 2013 - link
From a handset design perspective, SIM cards are not desirable either, but they are required for GSM devices. There has been a steady push to make them ever smaller and reduce their voltage requirements, which is why we went from full-size SIM, to mini-SIM, to micro-SIM, and now to nano-SIM. microSD card slots require at least 212 mm^3 of interior volume and 137 mm^2 of PCB real estate. Apple's nano-SIM tray has a volume of right around 200 mm^3 and occupies about 148 mm^2 of PCB, so very similar footprint, but that's for an externally accessible tray and receptacle. And if you look at a picture of the logic board, you'll see why this is such an issue—it's actually the single largest component on the entire board: http://d3nevzfk7ii3be.cloudfront.net/igi/UXZEPCS1l...The volume of an iPhone 5 battery is 9207 mm^3. Adding a second tray that could accommodate a microSD card and enough additional logic board to mount it on would consume some 540 mm^3 of internal volume, which is 5.9% of the volume occupied by the battery. By comparison, the volume of the SGS4 battery is ~13681 mm^3 with the microSD slot taking up nearly 600 mm^3, yet only representing 4.4% of the battery volume. Even though the penalty is lesser on a larger device, it is still a significant trade-off.
Hairs_ - Thursday, November 28, 2013 - link
While quoting the numbers looks good, adding an extra few mm to the thickness/width of the device would easily make up for the volume lost to the SD and Sim slots. Furthermore, where do you see these manufacturers jumping for the extra 5.9% battery volume? And assuming they do, gaining a significant real-world advantage in battery life?Fractured and overloaded mobile networks have a much bigger effect on mobile battery life than the loss of volume you're lamenting. For an easy example, switch off mobile data on your device and see how much longer it lasts (don't use any data applications for the same time period for a control test).
The iPhone5 would be far better served by being a little bit wider and accommodating a larger battery that way, than the relatively insignificant size of adding an SD card slot. Who would lose? Nobody. Who would gain? Consumers currently being charged quadruple the going rate for a memory upgrade.
repoman27 - Wednesday, December 4, 2013 - link
I didn't quote those numbers, per se. I actually made some measurements and did a few calculations. If I had quoted them, the volumes probably would have been stated more properly using ml rather than mm^3 for units.And you are absolutely right; adding a few mm to the thickness of a device can create the necessary interior volume for any number of additional features. However, all smartphones could accommodate a battery that could last for 3 days on a single charge if they were just a tad thicker and a bit heavier. Nobody would complain if their smartphone ran for 3 days off a single charge. However, no OEM has shipped a flagship smartphone with a battery that lasts this long. Why is that?
There is a direct correlation between the volume of a battery and the maximum amount of energy it can provide. Using the most power efficient components in a device and tweaking the OS may allow you to get better milage or get by with a smaller gas tank, but the battery size / battery life correlation remains the same regardless. If the battery stays the same, microSD card slots inherently increase the size, weight and cost of a device. If the size and weight stay the same at the expense of battery volume, microSD card slots inherently reduce battery life. Most users of smartphones that ship with an empty microSD card slot never install a microSD card. Therefore most users would suffer from reduced portability or decreased battery life if, for instance, the iPhone 5 had a microSD card slot.
The notion that consumers are simply being charged 4x the going rate for higher capacity storage in smartphones is a bit simplistic. If you took the BOM cost of the NAND flash memory modules shipped in all the current smartphones, and added the average gross margin for their respective OEMs, what sort of price tiers would you expect to see? They would obviously be much higher in terms of cost/GB than the cheapest microSD cards on the market, but also pretty far from the typical $50 or $100 steps we tend to see with smartphone pricing. On the other hand, is it inherently bad that the base model is generally subsidized by the fatter margins on the higher tiers in order to hit that entry level price point? And don't the street prices for the higher storage tiers end up being even more outrageous for smartphones with microSD card slots? The benefits of microSD card slots are that they allow the user to defer spending on additional storage, reuse storage modules for multiple devices, potentially add more capacity than available via configurations offered by the OEM, save money by using lower quality or lower performance memory, buy modules on the open market where sellers might take considerably lower margins, take advantage of pricing opportunities created by the volatility of the NAND flash memory market, and take advantage of Moore's law delivering a halving of price or doubling of capacity every 24 months. The downside is that they can also be a cop out for OEMs looking to reduce SKUs and not build as many devices with more costly, higher capacity NAND flash modules for those customers who are willing to pay for storage that offers higher performance, increased reliability, and tighter integration.
Hairs_ - Monday, December 9, 2013 - link
"However, no OEM has shipped a flagship smartphone with a battery that lasts this long. Why is that?"Because OEM's are
a) Nickel and diming on parts
b) Using artifically limited battery capacities to make a killing on "optional" extras like charging stations/"battery covers" etc.
c) Not very focused on what consumers actually ask for.
Pick any or all of the three. All are far more likely than an OEM saying "Oh woe is me, if only I didn't have to let users replace their batteries, I could save that huge rectangular space and fit in some extra battery that I couldn't possibly get anywhere else, especially not, say, by increasing the overall depth of the device by a single millimetre."
"The notion that consumers are simply being charged 4x the going rate for higher capacity storage in smartphones is a bit simplistic."
Good thing it's not easily demonstrated by publicly available facts, then.
"The downside is that they can also be a cop out for OEMs looking to reduce SKUs and not build as many devices with more costly, higher capacity NAND flash modules for those customers who are willing to pay for storage that offers higher performance, increased reliability, and tighter integration."
Did you miss the many, many, many posts which pointed out the easily researched fact that microSD cards are actually *faster* than the storage in top of the range premium phones/small tablets? And have higher capacities? Are you just ignoring these easily verifiable facts?
repoman27 - Monday, December 16, 2013 - link
You shoulda) look at the effect on the BOM cost that a larger battery would make and weigh that against the impact of battery life on unit sales
b) look at the balance sheet of any handset OEM to see how that "killing" on optional extras compares to the profit from sales of the primary device
c) not even joke about focus groups being a good idea
Why don't you take a minute to click on the "Bench" link up at the top of this page and take a gander at the Android smartphone storage benchmarks.
Let's start with the Samsung Galaxy Note 3, which posts sequential reads of 107.24 MB/s, which is faster than the UHS-I interface. In fact, everything released in the past year is north of 48 MB/s. Then let's look at the 4 KB random read performance, which across the board shames every microSD card on the market because they simply aren't designed for it. Then let's look at 4 KB random writes, where the Galaxy Note 3 and Moto X both exceed 500 IOPS, something that no microSD card can boast. And finally you come to the sequential writes, which are in fact disappointing on most smartphones, however this is one of the metrics that is targeted for optimization on SD cards.
Feel free to compile a list of 32 and 64 GB microSD cards that exceed the performance of the NAND modules in flagship smartphones in any metric other than sequential write speed. Make sure to note the retail price of those cards as well. What is the rated endurance of the NAND they use? How robust are the wear leveling algorithms or encryption protocols they incorporate?
I own Sandisk Extreme and Lexar 600x cards, so I'm pretty familiar with both the performance and pricing of the fastest microSD cards on offer. My last 3 phones all came with 64 GB of integrated storage, but I've yet to come across a 128 GB microSDXC card, and only recently has the performance of 64 GB microSDXC cards caught up with what you've been able to get in phones for years.
stop-a - Tuesday, November 26, 2013 - link
Since this is Anandtech, all opinion from Anand/Brian must have been right.Wait, Samsung is still selling phones with fully swappable micro-sd & batteries and they are the no.1 Android phone maker in the world. So Samsung must listen to Anand because only Anand could be right.
Message to Moto, modular phone idea is stupid according to Anand, you must stop your project right now, cause all phones must be uni-body design.
solipsism - Tuesday, November 26, 2013 - link
Yes, Anand and Brian's opinions are right BECAUSE THEY ARE OPINIONS, just as if you stated your opinion was preferring SD-cards, dual-headphone jacks, and having an eInk display on the backside of your device. Since it's an opinion you have a right to it no matter how silly it is, but for you to sarcastically suggest that Anand and Brian's opinions mean they are wrong to have factually shows you don't quite understand what an opinion is.