The price ($230 USD) is surprisingly tame and the Class 10 speed promises sufficiently aggressive performance

After decades of declining costs and soaring capacities, flash smartphones have finally reached a crucial milestone, with microSDXC solid state storage capacity finally topping the mechanical hard disk drive (HDD) solutions found antiquated, but beloved personal music player (PMP) models of years past.

I. A New Record in Commercial Mobile Flash Storage

True to its teaser at the 2015 Mobile World Congress (MWC) in March, SanDisk Corp. (SNDK) launched its 200 GB, Class 10 "Ultra" microSDXC card before the end of Q2.  What's perhaps most surprising is the price.

SanDisk 200 GB

Currently retailing for $239 USD on, Inc. (AMZN) ($249.99 USD MSRP), the card won't break the bank.  The card comes with a solid spec that includes:
  • 10-year-limited warranty
  • SD slot adapter
  • waterproof, temperature-proof, shockproof, X-ray-proof, and magnet-proof certifications
Sandisk hardy
  • 90 MB/s read speeds (or as SanDisk puts it, roughly 1,200 pictures/minute)
  • Automatic backup options
  • 200 GB of storage (enough to store 20 hours of 1080 (1,920x1,080 pixel; aka "full HD" or FHD) video)
That's pretty impressive.


The storage firm's marketing VP, Dinesh Bahal, comments:

We continue to push technology boundaries to deliver record-breaking solutions that transform the way consumers use their mobile devices.  By focusing on achieving new capacity and speed milestones, we are able to deliver trusted mobile memory solutions that give consumers the freedom to never stop capturing, saving, or sharing – with the benefit of fast speeds to transfer it all quickly.

SanDisk is currently leading the industry in terms of stacking NAND flash into high-capacity microSD storage.  It was the first to introduce a 128 GB microSDXC card, doing so back in Feb. 2014.  

II. Under the Hood -- The Technology Driving This Record Holder

SanDisk's success is largely in its strategy.  Intel Corp. (INTC), Toshiba Corp. (TYO:6502), and Samsung Electronics Comp., Ltd.'s (KRX:005930) (KRX:005935) having reach the limits of planar NAND flash at around 128 Gigabits (Gb) (16 Gigabytes (GB)) per die on a 20 nm process, have been pushing hard to develop vertical-NAND -- special 3D NAND structures that pack twice or three times the bit-levels per die in the stack.

Toshiba's current v-NAND stacks are 128 Gb (16 GB) based on a 32-die layer stack of single cell flash.  Samsung's designs are a bit more advanced w/ 256 Gb (32 GB) and 384 Gb (48 GB) 32-layer designs, based on two- and three-bit multi-layer cell (MLC) designs.  While this technology has crept into high end solid state drives (SSDs) for the PC, Intel, Samsung, and Toshiba have yet to successfully downsize it to smaller form factors while retaining the number of layers and bits per cell as in the larger SSD-destined chips.

Sandisk new chip relies on repurposing older planar dies in a similar spirit.

Rather than trying to print a single monolithic 3D flash chip with dozens of layers, Sandisk instead cobbles together 128 Gigabit (8 GB) planar dies via internal interconnects.  This approach has challenges of its own in the real world, however thus far it seems to be serving Sandisk quite well.


Samsung also uses this approach, as this Chipworks blog explains.  However, it appears to be struggling to scale it to taller stacks.

The Chipworks blog from 2010 hints that one key cause of SanDisk's growing lead in the small form factor capacity is thanks to its superior die thinness.  SanDisk's 2009-era stack from a 16 GB microSD card had a mere 30 µm in thickness.  By contrast, Samsung's 32 GB stack for the iPhone 4 in 2010 reported struggled to achieve anywhere near that level of thinness -- and was relatively inconsistent to boot.  It had chips that varied from 55-70 µm in thickness.  As the number of chips in the stack grew, Samsung has been unable to keep up with SanDisk's proprietary razor-thin stackable dies.

 That said, it hasn't been all smooth sailing for SanDisk either.  After Apple, Inc.'s (AAPLdecided to tap SanDisk's tri-level cell (TLC) based stacked NAND, rather than Samsung's MLC stacks for use in the 128 GB iPhone 6/6+ flagship device SKUs, it was forced to fall back to Samsung and other suppliers after a batch of SanDisk chips proved defective, causing devices to get stuck in fatal bootloops.  (Further Kbench test results showed that Samsung's 64 GB chips significantly outperformed the 128 GB SanDisk TLC chips, as well.)


SanDisk's v-NAND stack of multilayed BiCS2 cell is pictured.

That embarassment, aside the stacked-thin die approach has allowed SanDisk to keep cost down and rapidly deploy small form-factor storage solutions, including multi-die stacked NAND-based microSD cards.  Last Feb. SanDisk introduced the world's first 128 GB microSD car.  That design was based on 16 stacks of 64 Gb (8 GB) NAND.  Assuming this is a similar design, SanDisk is likely using a 25 chip stack of 64 Gb (8 GB) NAND dies for the 200 GB microSD card.

That said, SanDisk is only relying on this approach -- well done as it may be -- on the high end of mobile storage.  It has announced plans of its own to have commercial v-NAND deployed by next year.

Like Toshiba, SanDisk describes its technology as BiCS2 (bit-cost-scaleable second generation).  Both have 48-layer solutions in the works for 2016.


Toshiba BICS

Toshiba sandisk

SanDisk's lead may be short lived.  A company called Microdia Ltd. -- based out of the Kowloon of Hong Kong and San Jose, Calif. -- plans to begin offering 256 GB and 512 GB "Xtra Elite" microSD cards next month.  However, SanDisk will almost certainly still have Microdia beat on volume and price.  The Microdia Xtra Elite cards are expected to be low volume, retailing for as much as $1,000 USD for the 512 GB model.

Microdia's cards do offer "Ultra High Speed" (UHS) bus support, which adds an extra row of pins to boost chip speeds as a high as 300 MB/s for reads (theoretically).

III. What This Means for the PMP Market

Some may wonder why we should all care about microSD storage in the first place?  One key target is the PMP market.  While cloud storage capacities have lessened the utility of large capacity MP3 players, for audiophiles and music enthusiasts with large libraries, there's still a good deal of demand for local storage.

To date the best solid state storage capacities are found in a handful of smartphones with 128 GB of internal NAND flash.  Those include SKUs of Samsung Electronics' flagship Galaxy S6/S6 Edge smartphones and Apple's iPhone 6/6+ devices.  (Or alternatively, get an Android flaship model with 32 GB of internal storage and a 128 GB card for a grand total of 160 GB.)

It's taken flash memory more than half a decade to catch up with HDD based PMP.  For that reason there's still a relatively lively demand for the 160 GB Apple iPod Classic, which debuted in 2009.  The PMP recently has been averaging around $200 USD used on eBay, Inc. (EBAY) (if you have the original packaging, etc.) and $300-400 USD for new units.
iPod Classic
The iPod Classic 160 GB model remains a popular seller.

Other options included the recent 256 GB/500 GB/750 GB/1 TB "Hyper" line of PMPs from Fremont, Calif.-based Sanho Corp.  Players that used SD cards have become another compelling iPod alternative for audio enthusiasts in the past several years (ever since 128 GB SD cards started popping up around 2011).

While some solutions are supposedly in the works -- e.g. the "Saygus V2" smartphone -- their chance of making it to market is more questionable.  Saygus, for example, has yet to deliver its high-capacity smartphone, which was original rumored to debut earlier this year.  Instead Saygus bumped the spec from 320 GB of NAND storage to 486 GB and took the project to IndieGogo.  The fact that it raised $1M USD, reflects how much Android users want high-capacity storage solutions.

For those who want more of a surefire possibility, and perhaps something with substantially better sound quality, the new 200 GB microSD cards offer a lot of possibilities not just in Android and Windows Phone devices, but also in premium PMP devices, many of which are based on expandable microSD storage.

Two examples I would recommend checking out are include:

FiiO X1
$100 USD
1x microSD (* 128 GB @ $180 USD; 200 GB @ $330 USD)

FiiO X1

FiiO X3
$200 USD
1x microSD (* 128 GB @ $280 USD; 200 GB @ $430 USD)

FiiO X3

FiiO X5
$200 USD (* 400 GB @ $760 USD; 256 GB @ $460 USD)
2x microSD slots

FiiO X5

*given the retail prices of SanDisk's 128 GB ($80 USD) and 200 GB ($230 USD) cards.

Both of those units should sound significantly better than your old iPod Classic as they pack high end audio processing components.  I suggest those interested also check out QLS's HI-FI QA350 V2 PMP ($257 USD), which is based on SD (hence somewhat cheaper) and is built with similar high-end quality audio components as the FiiO units.
QLS Hi-Fi QA350 V2
And remember, SanDisk and Microdia's cards are just the start; the microSDXC standard supports capacities of up to 2 TB.  When it debuted in 2004, microSD's initial capacity was a mere 128 MB.  In the decade since, that capacity has grown more than 1,000-fold.  Hence history would suggest it'll only be a matter of time before 1 TB and 2 TB microSD cards come a-knocking.

Sources: Amazon [product page], SanDisk

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