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Flash storage in post-PC devices advances

Flash storage in post-PC devices advances

Size, power consumption and durability helped to make tablets and smartphones possible

Solid-state storage has helped to raise the wave of portable PC alternatives that has hit the market over the past few years, and 2011 is likely to see that technology become more affordable and better performing.

All the major tablets that have been announced or shipped this year use flash chips in place of a spinning hard disk drive (HDD) for storage. All smartphones also use NAND flash, as do many netbooks. Just as these types of devices won't wipe PCs out of the market in the next five years, flash won't displace HDDs in the foreseeable future. But what happens to flash storage affects a growing proportion of the digital tools used for work and play.

A move from spinning disks to flash chips brings benefits in three areas that are key to mobile devices: size, power consumption and durability. It also tends to reduce heat, which makes fans less necessary, and cut down on device startup time. The biggest downside of the technology is cost: A gigabyte of flash storage costs approximately eight times as much as the same amount of space on an HDD, according to Forward Insights analyst Gregory Wong.

That's one reason why Apple's iPad, which can cost as much as some Windows laptops, has a puny built-in storage capacity (in PC terms) ranging from 16GB to 64GB. Samsung's Galaxy Tab Android tablet comes with 16GB or 32GB of storage, with a port for expanding its capacity by another 32GB. The biggest HDDs are now advancing from 2TB to 3TB.

Yet buyers are willing to pay a per-gigabyte premium for these devices, partly because of svelte design, relatively long battery life and freedom from the long startup processes of full-fledged PCs. They also get storage that is less likely to fail if a device is banged or dropped, because it has no moving parts. Another justification may be that these consumers plan to use their new devices as adjuncts to the PC, where their main stores of data still reside.

Though HDDs themselves continue to get cheaper per gigabyte, coming advances in flash storage may help post-PC devices to take more ground from PCs, industry analysts say.

For one thing, flash is getting more dense. Following the same principles that are at work in ever-faster microprocessors, makers of flash chips continue to use tighter manufacturing processes. For example, in early 2010, Micron Technology began commercially shipping flash chips made with a 25-nanometer process, said Glen Hawk, vice president of the company's NAND Solutions Group. Without being more specific, Hawk said Micron expects to ship its next-generation chips about 18 months after the 25-nanometer introduction.

Samsung Semiconductor says it is using a process below 30nm and progressing toward one in the "low twenties," according to Steve Weinger, director of marketing for flash technology. "Things will happen this year," he said.

As with microprocessors, smaller means not just faster but less expensive for a given performance. Currently, Micron's 64GB SSDs (solid-state drives) sell for about US$130, but within about 18 months, prices will probably drop to about $100 for an SSD twice as big, at 128GB, Hawk said.

But as the technology gets more dense, it also gets harder to manage. Flash stores data by using a high-voltage pulse to alter the charges on individual cells, and the more tightly those cells are packed, the harder it is to "write" the correct charges to the right ones. This is a bigger problem in the type of flash that ships in consumer gadgets and client devices, which has multiple bits on a single cell. There's a limit to the number of times the cells can be modified, so the capacity of a storage device can decline over time.

The flash storage in today's client devices will last five years or more with the typical rate of writing by consumers, vendors and analysts said. That is longer than most people keep their client devices, but the challenge is to maintain that durability as components get more packed in.

"As we shrink our dies, the endurance basically tends to shrink with it," Samsung's Weinger said. However, there are ways to make this work without slowing down the flash, he said.

So far, vendors have been addressing this problem with smarter software in flash controllers, which manage the writing and reading of data, said Henry Baltazar, an analyst at The 451 Group. Earlier controllers would write the same data multiple times until it was written correctly, which accelerated the chip's decline, he said. In the past year, controller vendors such as SandForce have developed more efficient controllers that write the data correctly the first time, Baltazar said.

In 2011, vendors will start to add DSPs (digital signal processors) to improve the accuracy of the data being written to flash, Baltazar and others said.

That would mark a further step beyond correcting errors that have been made, toward preventing data-writing problems in the first place, Micron's Hawk said. Actual DSPs, which have so far been used in voice processing and other applications, are just one tool for doing signal processing, he said.

"We are doing some fairly light things today, as are most people. But very quickly we will be deploying very, very advanced algorithms and techniques in signal processing," Hawk said. He expects those advances to come in the company's next generation of flash, due in about a year.

The interfaces between devices and flash storage are also accelerating, according to Samsung. The company's products recently advanced form SDR (single data rate) interfaces, which could execute transfers at 40M bps (bits per second), to DDR (double data rate), at up to 133M bps, Weinger said. The next step will be to 400M bps, allowing users to get to their data even faster.

Successive generations of chips are also more power-efficient. Samsung expects the voltage of its flash to move from 3.3 volts to 1.8 volts, giving system manufacturers a tool to extend the battery life of their devices, Weinger said.

All these factors should translate into tablets, smartphones, netbooks and other devices that are more appealing and less expensive, or that offer more for the same price. But this doesn't necessarily mean post-PC devices will be better able to displace laptops, analysts said. For one thing, some laptops already come with SSDs. And while SSDs improve, HDDs will also offer more capacity for less money.

"It's a moving target. Hard drives aren't just sitting around," Baltazar said.

However, the way users store data is shifting from keeping it all on one PC to a more distributed approach, analysts said. They may keep a large amount on a central platform such as a home or corporate server, a small amount on a highly portable device with flash, and an increasing amount in the cloud, said analyst Roger Kay of Endpoint Technologies Associates.

"If you have lots and lots of very cheap storage available that's online ... then the need to carry it around is a lot less," Kay said. Given the other alternatives, anything over 100GB of storage is probably adequate for the device the user always carries around, Kay said.

So between stationary storage capacity and cloud storage, there may be an opportunity for various devices with smaller amounts of flash storage, rather than a large HDD, to become the mobile user's companion, analysts said.

But whether users will migrate to post-PC devices, which generally lack complete file systems and some other features, will depend at least as much on other factors, they said.

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