SanDisk has found a way to squeeze 128GB of flash storage into an external drive that's smaller than our smallest coin. Forget the thumb drive; this is a thumbnail drive.

The SanDisk Ultra Fit isn't a new form factor; it debuted last fall in 16GB, 32GB, and 64GB varieties. But 128GB in a pebble-sized drive represents a significant capacity-to-size breakthrough. That is, after all, the same amount of storage you'll find in a baseline MacBook Air (or, for that matter, top-end iPhone). It's enough space to fit up to 16 hours of full HD video, or over 18,000 standard MP3s.

The way SanDisk pulled off the pint-sized drive, according to director of product marketing Phillippe Williams? Thinking tall, not wide, and being able to take advantage of every last centimeter.

"Using proprietary technologies, our memory die are vertically stacked—each of which is shaved to be thinner than a strand of hair," Williams explains over email. "Fitting more memory into the same form factors is one of our in-house skill sets... While Moore's Law allows us to regularly increase capacity, the work we do on packaging and product design accelerates this."

The stacking of flash memory calls to mind Intel and Samsung's recent 3D NAND approaches to flash-based solid state drives, just in a form factor that's more appropriate for a keychain or, more realistically, permanently housed in your laptop's USB slot. The Ultra Fit is intended as a "plug-and-stay" device, acting as an ever-present storage boost rather than a portable solution. Just as well; the more you have to keep track of something this minuscule the more likely you are to lose it in the couch cushions, or find it in the front pocket of a pair of freshly washed jeans. It's never been easier to misplace $120 worth of gadget.

SanDisk

The idea of a small form factor bestowing big storage gains on an existing notebook has plenty of appeal, too, as newish formats like hi-definition audio and 4K video and endless smartphone photographs saddle us with more GB of data than we know what to do with. The cloud is a great option, but it's both costly and often burdened by slow streaming or download times.

"You could see this as being particularly attractive in emerging markets, where price is an even more important consideration," says Williams. Although given the cost savings, that may actually undersell the appeal. Stepping up from 128GB to 256GB on otherwise identical MacBook Airs costs $200, a full $80 more than just buying the base model and augmenting with an Ultra Fit. If you're comfortable with a decent drop-off in read speed for non-essential files (an 11-inch 2015 MBA SSD notches 315 MB/s, versus the Ultra Fit's 130MB/s), it's a no-brainer. Even more so when you consider less traditional gadgets that have USB ports these days; plopping one of these in your car would give you enough onboard music to road trip your way to Siberia.

The potential downside, other than the fact that you'll almost certainly misplace it the first time you remove it from its port of call? While USB 3.0 remains the industry standard, it's increasingly giving way to the smaller USB-C in products like the new MacBook. Since USB-C isn't backwards compatible, there's a chance that this flash drive's lifespan is destined to be only as long as your current computer. And when USB-C finally does eclipse USB 3.0 entirely, there's some question as to whether plug-and-stay devices will be feasible at all, since you'll also use that port for charging your device, hooking up to external monitors, and, well, pretty much everything else.

That's still a few years away though. For now, you can feel comfortable in marveling in a flash drive that feels more like a tiny data-packed TARDIS; small and unassuming on the outside, but containing larger worlds than you ever thought possible.