In part one of our "SSD Revolution" series , we covered the basics of flash memory in solid state drives, walking through lots of important but esoteric details such as the difference between NAND flash and NOR, or how SSD reads and writes work. We also talked about the techniques used to make SSDs faster and to prolong their lives. But SSDs don't just exist in a vacuum—the state of solid state, such as it is, has had a significant effect on the shape of the modern mobile device landscape, which we explore now in part two.

Not long ago, flash-based MP3 players occupied the low end of the capacity spectrum and, while some brave souls were using PCMCIA compact flash cards in their laptops, you still needed a real hard disk drive to effectively boot and use Windows or OS X. Not anymore—not only are flash-powered, high-capacity MP3 players and laptops standard, but modern operating systems are quickly adapting to SSDs as the norm.

An entire class of ultrabooks—which, in spite of what the name suggests, do not contain hyperdrives, organic CPUs based on alien DNA, or anything else truly deserving of the "ultra" prefix—are now built around the MacBook Air's design philosophy of being durable, thin, light... and stuffed full of NAND flash. Laptops of this form factor seem poised to deliver on most of the promises that netbooks once made (especially portability and battery life) without falling prey to the same set of compromises that ultimately doomed netbooks to hobbyist devices.

Tablets, too, are on the rise. The tablet segment of the mobile device market didn't even meaningfully exist prior to 2010—say what you will about the iPad, but it truly sparked a revolution. Since their rise to prominence, all mainstream tablets have been exclusively flash-powered devices; there's not a hard disk to be found anywhere in the lot. While the SSD craze might be sweeping the "real" computer segment as flash storage becomes more common on desktops and laptops, the place where NAND flash most truly empowers consumers is in mobile devices.

But things were not always thus, and flash wasn't always the best choice for mobile devices to store data.

CmdrTaco's gaffe

One of the most-parodied comments in the history of the Internet appeared on October 23, 2001 on tech blog and aggregator site Slashdot. Apple had just announced something called an iPod, with which they it hoped to take on the already-crowded portable music player market. In the news post about the iPod launch, Slashdot editor and founder Rob Malda (known by his net handle CmdrTaco) famously wrote, "No wireless. Less space than a Nomad. Lame."

At the time, he had a point. That initial iPod contained a 1.8" hard disk drive (the discontinued MK5002MAL) manufactured by Toshiba, which provided 5GB of space to store music (or anything else, really, since the iPod's FireWire connection meant it could be used as a fast and relatively cheap external hard disk drive). Though CmdrTaco was certainly correct that the competing Creative NOMAD Jukebox had more usable capacity, he swung and missed on which player would win the market because he made the common geek mistake of believing that a device's laundry list of features will tell the story of its success. Even though it had less space and didn't do wireless syncing (a feature that wouldn't show up on iOS devices until 2012!), the iPod was a heck of a lot easier to put in your pocket.

A look through the comments attached to that old Slashdot story paints a scene utterly foreign to most folks today. Yes, flash-based portable music players existed back in 2001, a time so long ago that a big chunk of today's hipster digerati were still in junior high, but those flash-based players had capacities measured in the dozens, or at best hundreds, of megabytes. A 64MB music player couldn't carry around much more than a CD or two of songs; the biggest 256MB players weren't that much of an improvement. Flash just wasn't ready for such uses, and if you wanted to take a substantial chunk of your music collection around with you, you needed a player with a hard disk drive.

I've said more than once that hard disk drives are miraculous machines, manufactured to incredibly tight tolerances and requiring extreme precision. Putting a spinning hard disk drive into a portable device which is going to bounce around clipped to your hip while jogging, therefore, is just about the worst possible thing you could do to the drive. Hard disks work best and most reliably when they're placed flat and don't move, since even tiny vibrations can bounce the drive heads around as they sit suspended on an air cushion just a few nanometers above the spinning platters, trying to focus on data tracks that are themselves only a few nanometers wide. The hard drives used in portable devices had to be treated carefully and used in very specific ways.

That first-gen iPod, for example, didn't keep its drive spinning constantly like a desktop or laptop computer does. In addition to saving on battery power, keeping the drive spun down when not needed kept the heads safely parked in their landing zones rather than hovering over the data surface of the disk, into which they might crash if sufficiently jarred. When music was played, the drive would quickly spin up, read as much of the current song and the next song into the iPod's RAM as it could, and then spin down again. Assuming you were listening to a playlist and not rapidly clicking through your library, the disk spent most of its time spun down and the iPod just played data out of RAM.

Flash-based players don't require such an approach. Flash media is solid state, so it doesn't have a motor; it also doesn't particularly care whether or not it's being vibrated to death. It's entirely possible to take a hard disk player like an iPod Classic or a Creative Nomad and cause them to freak out by shaking them vigorously while changing tracks; flash doesn't care. If only it could be produced with higher capacities...

Moore's Law marches on

Times change, progress happens, and every couple of years or so the amount of transistors you can cram into a given amount of space tends to double. Hard disks fit the bill for portable devices for quite some time after the portable music player market began to explode, with 1.8" disks giving way to even smaller "microdrives" (Toshiba's 2004 press release about its 0.85" hard disk makes for a fun read, predicting that the drive will soon be used in "handhelds and smart phones"—which was true, though not for very long). Even as late as 2005, it seemed certain that the smart phones of the future would be powered by a teeny-tiny little hard disk drives, with Samsung and others proceeding full steam ahead with production plans.

Teeny-tiny little hard disk drives are amazing in their own right, but in the last half of the 00s (the Aughties? Is that what we're supposed to call them?), their capacity and their speed was surpassed by solid state. Flash has always been a better choice for portable devices because of its lower power consumption and insensitivity to vibration; so as flash capacity ramped up, hard drives for portable devices lost their one remaining advantage. Any future that microdrives had in the mobile space was quickly stomped flat by the 2007 release of the first-generation iPhone, which used 4 and 8 GB of NAND flash as its medium of choice for storing music, pictures, videos, and later apps and ringtones. Within a year, every other smartphone manufacturer in the world began to release something that looked, sounded, and smelled like an iPhone; designers abandoned all thoughts of using anything other than NAND flash.

It became like a closed feedback loop: as more manufacturers demanded to use flash in their devices, more flash needed to be produced; as more flash needed to be produced, it became worthwhile to accelerate research and development efforts in order to figure out how to make it better and cheaper, so more could be sold. From 2007 on, the mobile device market skewed exclusively in the direction of flash.

These days, portable devices with 32 or 64 GB of flash can be found everywhere. Tablets like the iPad are powering their way into homes and businesses, and solid state disks in laptops are becoming as common as spinning hard disk drives. Ultrabooks, driven by the sales success of the 2010 and 2011-generation MacBooks Air, all have flash in some form or another; some have hybrid disks, others are SSD-only.

It's certainly safe at this point to say that flash has won the war in the mobile space—I don't think we'll ever see another tablet or phone based on anything other than solid state storage. The war for the proverbial desktop (which includes most laptops) is far from over, with hard disk drives still outnumbering SSDs in most traditional computers. Still, SSDs are in enough places doing enough things that modern operating systems have changed to accommodate them.