Flash Technology Independence; Defect And Error Management; Copyright Protection - SanDisk SDSDB-32-201-80 - Industrial Grade Flash Memory Card Product Manual

Introduction to the SD Card

1.5.1. Flash Technology Independence

The 512-byte sector size of the SD 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 SD Card. This
command contains the address. 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. Because the SD Card 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 the SD Card today will be able to access future SanDisk SD Cards built with new flash
technology without having to update or change host software.

1.5.2. Defect and Error Management

SD 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 the performance penalty that would be
incurred. SD Cards do a read after write under margin conditions to verify that the data is written correctly. In the
rare case that a bit is found to be defective, SD Cards replace this bad bit with a spare bit within the sector header. If
necessary, SD Cards will even replace the entire sector with a spare sector. This is completely transparent to the
host and does not consume any user data space.
The SD Card's soft error rate specification is much better than the magnetic disk drive specification. In the
extremely rare case a read error does occur, SD 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 SD Cards unparalleled reliability.

1.5.3. Copyright Protection

A detailed description of the Copyright Protection mechanism and related security SD Card commands can be found
in the SD Card Security Specification document from the SD Card Association. All SD Card security related
commands operate in the data transfer mode.
As defined in the SDMI specification, the data content that is saved in the card is saved already encrypted and it
passes transparently to and from the card. No operation is done on the data and there is no restriction to read the
data at any time. Associated with every data packet (song, for example) that is saved in the unprotected memory
there is a special data that is saved in a protected memory area. For any access (any Read, Write or Erase command)
from/to the data in the protected area. For an authentication procedure is done between the card and the connected
device, either the LCM (PC for example) or the PD (portable device, such as SD player). After the authentication
process passes, the card is ready to accept or give data from/to the connected device. While the card is in the
secured mode of operation (after the authentication succeeded) the argument and the associated data that is sent to
the card or read from the card are encrypted. At the end of the Read, Write or Erase operation, the card gets out
automatically of its secured mode.
1-4 SanDisk Secure Digital (SD) Card Product Manual, Rev. 1.9 © 2003 SANDISK CORPORATION