CompactFlash Memory Card Product Manual
SanDisk CompactFlash Memory Card Product Manual Rev. 7 © 2000 SANDISK CORPORATION10
1.7.1 Flash Technology Independence
The 512 byte sector size of CompactFlash Memory
Card is the same as that in an IDE magnetic disk
drive. To write or read a sector (or multiple
sectors), the host computer software simply issues
a Read or Write command to the CompactFlash
Memory Card. This command contains the address
and the number of sectors to write/read. The host
software then waits for the command to complete.
The host software does not get involved in the
details of how the flash memory is erased,
programmed or read. This is extremely important
as flash devices are expected to get more and more
complex in the future. Since the CompactFlash
Memory Card Series uses an intelligent on-board
controller, the host system software will not
require changing as new flash memory evolves. In
other words, systems that support t h e
CompactFlash Memory Card today will be able to
access future SanDisk cards built with new flash
technology without having to update or change
host software.
1.7.2 Defect and Error Management
CompactFlash Memory Cards contain a
sophisticated defect and error management
system. This system is analogous to the systems
found in magnetic disk drives and in many cases
offers enhancements. For instance, disk drives do
not typically perform a read after write to confirm
the data is written correctly because of t h e
performance penalty that would be incurred.
CompactFlash Memory Cards do a read after
write under margin conditions to verify that the
data is written correctly. If necessary,
CompactFlash Memory Cards will replace the
entire sector with a spare sector. This is
completely transparent to the host and does not
consume any user data space.
The CompactFlash Memory Card soft error rate
specification is much better than the magnetic
disk drive specification. In the extremely rare
case a read error does occur, CompactFlash
Memory Cards 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
CompactFlash Memory Cards unparalleled
reliability.
1.7.3 Endurance
With the introduction of the 256 Mbit Flash
Technology, CompactFlash Cards have almost
unlimited write endurance (reading a logical
sector is unlimited). This results in an added
benefit to the user where the anticipated life of
the CompactFlash products is now substantially
increased over the life of previous SanDisk
Binary Flash technology products.
1.7.4 Wear Leveling
CompactFlash Memory Card Series products 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
As a result of the CompactFlash Card’s almost
unlimited endurance, the Erase Sector and Write
Without Erase Commands are no longer supported.
There will be no net gain in the use of these
commands. Since the write performance of
SanDisk products typically improves with the
introduction of next generation flash technologies,
this feature is no longer required. Any platforms
employing these commands in previous SanDisk
products will not be affected as a result of the
elimination of this function. The Erase Sector
Command will still erase the sectors but t h e
Write Without Erase Command will perform a
normal Write Command resulting in no net gain in
write performance.