Technology Independence; Defect And Error Management; Wear Leveling; Using The Erase Sector And Write Without Erase Commands - SanDisk CompactFlash Product Manual

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Introduction to the CompactFlash Memory Card

1.6.1. Technology Independence

The 512-byte sector size of the 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 the 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.

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. If necessary,

CompactFlash Memory Cards will rewrite data from a defective sector to a good 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.

These defect and error management systems, coupled with the solid state construction, give CompactFlash Memory

Cards unparalleled reliability.

Wear Leveling is an intrinsic part of the Erase Pooling functionality of SanDisk CF using NAND memory. The CF

Wear Level command is supported as a NOP operation to maintain backward compatibility with existing software

utilities.

CompactFlash Memory Cards support the CF ERASE SECTOR and WRITE WITHOUT ERASE commands. In

some applications, write operations may be faster if the addresses being written are first erased with the ERASE

SECTOR command. WRITE WITHOUT ERASE behaves as a normal write command and no performance gain

results from its use.

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CompactFlash

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