SanDisk's Know-How Strengthens the SSD Industry

With an eye to benefiting the end user, SanDisk® provides the technology and measuring tools to hasten the adoption of solid state drives (SSDs) in PCs.

SanDisk's All Bit Line (ABL) architecture greatly boosts write performance and reduces power consumption by uniquely sensing the programming voltage in all word line cells simultaneously. Relying on non-volatile flash, SanDisk's innovative nCacheTM utilizes system idle time to improve overall responsiveness to user requests. SanDisk's flash management technology, ExtremeFFSTM, is specially tuned to help accelerate the performance and extend the endurance of SanDisk SSDs inside PCs that use full-featured operating systems.

SanDisk's industry metrics, LDE (Long-term Data Endurance) and vRPM (virtual Revolutions Per Minute), give users benchmarks to evaluate the endurance and performance of SSDs and vs. hard disk drives (HDDs) and other SSDs.

All Bit-Line (ABL) NAND Architecture
SanDisk's patented All Bit Line (ABL) NAND architecture vastly improves write performance and reduces power consumption in the SanDisk G3 SSD series of solid state drives.

Relative to conventional memory architectures, SanDisk ABL architecture boosts write performance by over 100%. It uses highly effective, advanced algorithms to achieve these outstanding results. They exercise all cells in a selected word line simultaneously, immediately sensing the programming condition of non-volatile storage elements. Less sophisticated architectures use every other cell in a consecutive rather than a simultaneous process, taking twice as long to sense when data has been written.

SanDisk ABL architecture reduces power consumption due to its efficient even and odd bit line voltage sensing.

Non-Volatile Write Cache (nCacheTM)
All HDDs and many SSDs use a DRAM write cache to allow the drive to quickly receive and acknowledge write commands back to the system, taking advantage of system idle time when the user is not waiting for responses. But the DRAM write cache does not always live up to this vision. Since data in DRAM is at risk from a sudden power loss, full-featured operating systems force the drive to flush the cache whenever it contains critical information. Windows can issue FLUSH CACHE commands as often as 30 times per second when the system is busy, greatly limiting the effect of the DRAM write cache.

SanDisk's innovative nCacheTM is a large, non-volatile write cache. As soon as data is written to the SSD, it is stored in non-volatile NAND flash that saves data reliably even in the absence of power. With no volatile cache, the SSD is not subject to the performance penalty associated with FLUSH CACHE commands.

SanDisk nCacheTM frees the write cache to operate as intended. It quickly receives and acknowledges writes back to the system in the background, when the user is not waiting on his system, to maximize system responsiveness. Since nCacheTM is implemented in NAND flash memory, it can be much larger than a DRAM cache. In some cases, it can provide enough write cache for 30 or more minutes of sustained user activity, realizing the original vision of a write cache.

ExtremeFFS (Extreme Flash File System)
ExtremeFFS has the potential to greatly extend endurance and accelerate SSD random write speeds by as much as 100 times compared with existing systems. Based on SanDisk's TrueFFSTM flash management system that was introduced in 1994 and incorporated into Windows 95 as the leading flash file system for major mobile handset vendors, ExtremeFFS applies a novel approach to flash management based on design elements such as:

• Page-based algorithm: Customized for popular operating systems such as Vista, ExtremeFFS uses a page-based algorithm with no fixed coupling between physical and logical location. This gives SanDisk SSD the freedom to store a sector of written data where it is most convenient and efficient.

• Fully non-blocking architecture: NAND channels operate independently as required by user activities, with some reading while others are writing and garbage collecting.
• User pattern learning: ExtremeFFS can learn user patterns to store data used with higher frequency in quickly accessible locations.

LDE (Long-term Data Endurance)
LDE is the first industry metric that expresses how long data can be reliably stored in SSDs in a measurable number. LDE was proposed by SanDisk as a benchmark to enable users to compare the data endurance of SSDs from various manufacturers. Based on typical end-user activity, LDE provides the total number of data writes, expressed in Terabytes that can be performed over the SSD lifespan. SanDisk offers a methodology that enables accelerated testing.

vRPM (virtual Revolutions Per Minute)
This is a new metric to enable users to compare SSD performance in client PCs with the HDD and with other SSDs. The beauty of vRPM is its simplicity. SanDisk chose to use RPM since it is a language that users understand, a defacto standard in the hard disk drive (HDD) world. However, since the SSD has no revolving parts, which cause the HDD to incur latency penalties, SanDisk modified RPM to vRPM. vRPM essentially answers the question: "How fast would you have to spin a virtual HDD to achieve the level of performance seen by an SSD in a client PC?" SanDisk's new vRPM metric results indicate that SSDs are faster than HDDs when performing random read and write operations.