SanDisk SD032 Manual descarregar pdf (Página 10)

1.5.2. Defect and Error Management

miniSD 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. SanDisk miniSD 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, miniSD cards replace this bad bit with a spare bit within

the sector header. If necessary, miniSD Card s 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 miniSD 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, miniSD Card s 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 miniSD Card s unparalleled reliability.

1.5.3. Copyright Protection

A detailed description of the Copyright Protection mechanism and related security miniSD Card commands can be

found in the mini SD Security Specification document from the mini SD 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 (e.g., a song) that is saved in the unprotected memory, there is

special data that is saved in a protected memory area for any access (Read, Write or Erase command) to or from 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.

1.5.4. Endurance

SanDisk miniSD Cards have an endurance specification for each sector of 100,000 writes typical (reading a logical

sector is unlimited). This far exceeds what is typically required in nearly all applications of miniSD Card s. For

example, even very heavy use of the miniSD Card in cellular phones, personal communicators, pagers and voice

recorders will use only a fraction of the total endurance over the typical device’s lifetime. For instance, it would take

over 10 years to wear out an area on the miniSD Card on which a file of any size (from 512 bytes to maximum

capacity) was rewritten 3 times per hour, 8 hours a day, 365 days per year.

With typical applications, the endurance limit is not of any practical concern to the vast majority of users.

1.5.5. Wear Leveling

SanDisk miniSD Cards do not require or perform a Wear Level operation.

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SanDisk SD032 Manual Página 10