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.