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.
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