System Features; Related Documentation; Functional Description; Flash Technology Independence - SanDisk SDIB-4 Product Manual

1.3

System Features

• Up to 440 MB of solid-state storage
• Fully MS-DOS compatible
• Very low power
• Very rugged
• Very low weight
• Noiseless
• Very high performance
• Programmable power versus performance
• 3.3V or 5V interface
• Block size of 512 bytes
• Supports automatic power management as
well as ATA power down commands and
sleep mode over the interface
• Automatic error correction and retry
capabilities
• Sophisticated defect management system
1.4

Related Documentation

American National Standard X3T9.2 AT
Attachment Interface Document
This document can be ordered from
Global Engineering Documents by calling
1-800-854-7179.
1.5

Functional Description

The SanDisk FlashDrives contain a high level,
intelligent subsystem as shown in the block
diagram, Figure 1-1. This intelligent (micro-
processor) subsystem provides many capabilities.
These capabilities include:
1. Standard ATA register and command set
(same as found on most magnetic disk
drives).
2. Host independence from details of erasing
and programming flash memory.
3. Sophisticated
defects (analogous to systems found in
magnetic disk drives).
4. Sophisticated system for error recovery
including a powerful error correction code
(ECC).
FlashDrive Product Manual © 1999 SANDISK CORPORATION
system for managing
FlashDrive Product Manual
1.5.1

Flash Technology Independence

The sector size of the FlashDrives is the same as
in a magnetic disk drive: 512 bytes. To write or
read a sector (or multiple sectors), the host
computer software simply issues a write or read
command. The command contains the number of
sectors to write/read
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. The
intelligent IDE compatible interface used by the
FlashDrives will not need to change to support
new flash devices in the future and therefore the
host software will not need to change. Systems
that support the FlashDrives today will be able
to access future SanDisk IDE compatible products
built with new flash technology without having
to update or change host software.
1.5.2

Defect and Error Management

The FlashDrives contain a sophisticated defect
and error management system. This system is
analogous to the systems found in all magnetic
disk drives and in many cases offers enhancement.
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. The FlashDrives do a read
after write under margin conditions to verify that
the data is written correctly (except in the case of
a Write without Erase command). In the rare case
that a bit is found to be defective the FlashDrives
can replace this bad bit with a spare bit. If
necessary the FlashDrives can 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 FlashDrive specification for soft error rate is
much better than the magnetic disk drive
specification. In the extremely rare case that a
read error does occur, the FlashDrives have
innovative algorithms to recover the data. This is
similar to using retries on a disk drive but much
more sophisticated. The last line of defense is to
employ a powerful ECC to correct the data. If ECC
and the address to
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