SDP3B FlashDisk Product Manual
SanDisk SDP3B FlashDisk Product Manual © 1998 SANDISK CORPORATION
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The SDP3B FlashDisk soft error rate specification
is much better than the magnetic disk drive
specification. In the extremely rare case a read
error does occur, SDP3B FlashDisks have
innovative algorithms to recover the data. This is
similar to using retries on a disk drive but is much
more sophisticated. The last line of defense is to
employ a powerful ECC to correct the data. If ECC
is used to recover data, defective bits are replaced
with spare bits to ensure they do not cause any
future problems.
These defect and error management systems
coupled with the solid state construction give
SDP3B FlashDisks unparalleled reliability.
1.7.3
Endurance
SDP3B
FlashDisks
have
an
endurance
specification for each sector of 300,000 writes
(reading a logical sector is unlimited). This is far
beyond what is needed in nearly all applications
of SDP3B FlashDisks. Even very heavy use of
SDP3B
FlashDisks
in
PDAs,
ruggedized
handheld computers, palmtop and notebook
computers will use only a fraction of the total
endurance over the typical computer’s five year
lifetime. For instance, it would take over 34 years
to wear out an area on the SDP3B FlashDisk on
which a file of any size (from 512 bytes to
capacity) was rewritten 3 times per hour, 8 hours a
day, 365 days per year.
With typical applications (PIM software, word
processing, spreadsheets, etc.), the endurance
limit is not of any practical concern to the vast
majority of users.
1.7.4
Wear Leveling
SDP3B FlashDisks do not require or perform a
Wear Level operation. The command is supported
as a NOP operation to maintain backward
compatibility with existing software utilities.
1.7.5
Using the Erase Sector and Write without
Erase Commands
The Erase Sector and Write without Erase
commands provide the capability to substantially
increase the write performance of the SDP3B
FlashDisk. Once a sector has been erased using the
Erase Sector command, a write to that sector will
be much faster. This is because a normal write
operation includes a separate sector erase prior to
write.
An example of where these commands may be
useful is in a digital camera. The camera user may
have plenty of time to erase pictures but may wish
to take several pictures in rapid succession. To
accomplish this, the host system (i.e., camera)
would use the Erase Sectors command to pre-erase
the sectors that will store the pictures. When the
pictures are taken, the camera can store them in
the previously erased sectors much faster than in
non-erased sectors.
1.7.5.1
Interaction with Systems not Aware of
the Erase Sector and Write without
Erase Commands
Many systems that can read and write SDP3B
FlashDisks may not be aware of the Erase Sector
and Write without Erase Commands. These
systems would not issue these commands but such a
system might attempt a normal write or a normal
read to a pre-erased sector.
A normal write to a pre-erased sector will function
correctly, but will be at the normal write speed
that is slower than a Write without Erase
command.
If a normal read is attempted to a “pre-erased”
sector, SDP3B FlashDisks will detect it is pre-
erased and will return zero data and will not
report an error even though the data ECC is not
valid.
If an “un-aware” host system over-writes a pre-
erased sector with a normal write and then the
SDP3B FlashDisk is moved to the system that
created the erased sectors, a situation exists
where a Write without Erase might be attempted
to a “normal” sector. If this occurs, the SDP3B
FlashDisk will perform a normal write which
means it will first erase the sector and then do a
full write with all margin modes enabled. This
write will of course be slower than if the sector
were in fact pre-erased.
