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Flash storage in post-PC devices advances

Stephen Lawson | Dec. 22, 2010
Size, power consumption and durability helped to make tablets and smartphones possible

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.


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