In future the MacBook Air will use lower-cost solid-state drives and the new generation of flash storage will reduce from a higher price today.Today, a consumer pays dearly for a solid-state drive (SSD). For example, for only 64GB of SSD storage on the MacBook Air, a consumer must pay a premium of about $1,000 over the 80GB hard disk drive model. But the cost per gigabyte of solid-state drive storage will drop as notebook PC makers like Apple switch to solid-state drives with capacities above 100GB based on multilevel cell (MLC) technology. Adoption by notebook PC makers is expected to start in the third quarter, according to industry sources.

All Solid State Device manufacturers have moved from the single-level cell (SLC), which is used in products like the MacBook Air, the ThinkPad X300 and HP 2510p to MLC technology.Intel is also set to move into the high-capacity SSD market on the back of its multilevel cell technology.

"Compared to the price you're paying today for a 64GB drive. You'll get a 128GB of storage for less than half the price (of the 64GB drive)," said Patrick Wilkison, vice president of marketing and business development at STEC, a supplier of MLC-based solid-state drives. The drives based on MLC technology offer better performance than hard disk drives. The current SSD manufacturers such as Samsung and Toshiba have also moved from single-level cell to multilevel cell.

MLC is a more sophisticated technology than current SLC. Its advantages are not only lower cost but higher capacity. Instead of the relatively small-capacity 64GB SLC-based drives being offered today in notebook PCs, manufacturers are targeting MLC-based drives ranging up to 256GB by the end of this year or early next year.

MLC NAND flash is a flash memory technology using multiple levels per cell to allow more bits to be stored as opposed to SLC NAND flash technologies, which uses a single level per cell. Currently, most MLC NAND stores four states per cell, so the four states yield two bits of information per cell. This reduces the amount of margin separating the states and results in the possibility of more errors. MLC NAND has the benefit of being cheaper due to the denser storage method used, but software complexity can be increased to compensate for a larger bit error ratio (BER).
The disadvantage is more complexity, which can result in lower performance. "Inherently, MLC is slower and inherently (has) less write cycling endurance," Intel has stated in the past.

Avi Cohen, managing partner of Avian Securities, sees it that way too. "You lose some speed and you lose some reliability when you move to MLC," he said. "Errors per cell with MLC is an order of magnitude worse than SLC, which isn't that great to begin with," Cohen said.

The higher BER requires an algorithm that can correct errors up to five bits and detect the condition of more than five bad bits. The most commonly used algorithm is Bose-Chaudhuri-Hocquenghem

A Single-Level Cell, SLC, memory card stores one bit in each cell, leading to faster transfer speeds, lower power consumption and higher cell endurance. The only disadvantage of Single-Level Cell is the manufacturing cost per MB. Based on that, the SLC flash technology is used in high-performance memory cards.

A Multi-level Cell, MLC, memory card stores three or more bits in each cell. By storing more bits per cell, a Multi-Level Cell memory card will achieve slower transfer speeds, higher power consumption and lower cell endurance than a Single-Level Cell memory card. The advantage of Multi-Level Cell memory card is the lower manufacturing costs. The MLC flash technology is used mostly in standard memory cards. The Multi-Bit Cell, MBC, is a similar technology to the Multi-Level Cell but stores only two bits per cell. Intel and STEC say they mitigate the reliability problem and boost performance with proprietary controller chips. "We spend 85 percent of our time grappling with this reliability issue" when talking to customers, said Wilkison. "NAND (flash memory) will forever have limitations. It will be subject to a finite number of program and erase (record and delete) cycles," he said.

"There's a lot of background operations happening to manage the media. Moving the data around to make sure you're evenly wearing down the drive. You're not necessarily pounding on one specific spot and then killing a (memory) cell prematurely," Wilkison said. "This is all controller intelligence."

The kind of technology to optimize the longevity of the drive is generally referred to as wear leveling. Error detection and error correction technologies are also used, Wilkison said.

Wilkison said he believes these techniques result in solid-state drives that are just as reliable as hard disk drives. And he expects a surge in adoption of solid-state drives in notebooks. Whereas today there is only one notebook model per company that comes with a solid-state drive, the number of models offered with such drives will increase exponentially in the second half of the year, he said.


There will still be a "price delta" between hard disk drives and solid-state drives but that will continue to come down with MLC technology, he said. Reports have cited Intel pricing as approaching $1 per gigabyte.

Solid-state drives have no moving parts. Hard disk drives, in contrast, use read-write heads that hover over spinning platters to access and record data. With no moving parts, solid-state drives avoid both the risk of mechanical failure and the mechanical delays of hard drives. Therefore, solid-state drives are generally faster and in some respects more reliable.

Samsung is touting the reliability of solid-state drives, while citing an explosive market for the devices in server computers.
SSDs are based on flash memory chip technology and have no moving parts. Hard-disk drives (HDDs), in contrast, use read-write heads that hover over spinning platters to access and record data. With no moving parts, SSDs avoid both the risk of mechanical failure and the mechanical delays of HDDs. Therefore, SSDs are generally faster and more reliable. The catch is the cost: SSDs are currently much more expensive than HDDs.

There are also concerns about wear. That is, flash has the potential to wear out after tens (or hundreds) of thousands of write cycles.

This characterization, however, is too simplistic, according to Michael Yang, flash marketing manager at Samsung. A flash device that is rated at 100,000 write cycles, for example, can write 100,000 times "to every single (memory) cell within the device," Yang said. In other words, the device doesn't write to the same cell over and over again but spreads out the writes over many different cells. This is achieved through "wear leveling," which is carried out by the SSD's controller, he said.

This would make it virtually impossible to wear out a flash chip. Yang said a pattern could be perpetually repeated in which a 64GB SSD is completely filled with data, erased, filled again, then erased again every hour of every day for years, and the user still wouldn't reach the theoretical write limit. He added that if a failure ever does occur, it will not occur in the flash chip itself but in the controller.

On another topic, Yang cited explosive demand in the enterprise server market that caught his company by surprise. "At first it just sounded like an interesting idea," he said. But then demand took off. As Yang explained, companies like Citibank and American Express peg server performance on IOPS or input/output operations per second. "HDDs do 120 to 150 IOPS. SSDs 10,000 to 30,000 IOPS." Because of this overwhelming speed advantage many large corporate customers are opting for SSDs, despite the significant price premium SSDs command compared with HDDs.

Regarding cost, Yang expects to see a 35 percent to 45 percent year-to-year drop in SSD prices. This will be a welcome relief since 64GB SSDs currently can add as much as $900 to the price of a notebook PC.

In the third quarter, Samsung is slated to bring out a 128GB SSD based on MLC (multi-level cell) technology--which uses multiple levels per cell to allow more bits to be stored. But the company sees even larger-capacity SSDs, ranging all the way up to 250GB, possibly before the end of the year.

The company is also working with notebook PC makers to design ultrathin notebooks with SSDs that can fit into potentially even thinner designs than the 0.76-inch thick MacBook Air, which uses SSD.

source:blogs.cnet.com