Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
2000-09-13
2004-08-03
Gossage, Glenn (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S202000, C711S209000
Reexamination Certificate
active
06772274
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of flash memory systems. More particularly, the present invention relates to flash memory systems implementing logical block address (LBA) to physical block address (PBA) correlation within a flash memory array.
BACKGROUND OF THE INVENTION
Flash memory technology is an electrically rewritable nonvolatile digital memory technology that does not require a power source to retain its memory contents. A typical flash memory cell stores charge on a floating gate to represent a first logic state in the binary state system, while the lack of stored charge represents a second logic state in the binary state system. Additionally, a typical flash memory implementation is capable of supporting a write operation, a read operation, and an erase operation.
As flash memory technology has evolved, opportunities in a variety of applications have become possible. In particular, flash memory implementations that emulate the mass storage function of conventional rotating magnetic media, e.g., a hard disk drive or a floppy disk drive, coupled to a host computer system or other host digital system have gained wide acceptance. Hard disk drives and floppy disk drives suffer several deficiencies unseen in flash memory implementations. First, hard disk drives and floppy disk drives have many moving parts, i.e. an electrical motor, a spindle shaft, a read/write head, and a magnetizable rotating disk. These components give rise to reliability problems and magnify the hard disk drive's and floppy disk drive's susceptibility to failure resulting from the vibration and shock of being dropped or bumped. Secondly, hard disk drives and floppy disk drives consume a significant amount of power, thus quickly draining a portable computer's battery. Finally, accessing data stored in the hard disk drive or the floppy disk is a relatively slow process.
In contrast, a typical flash memory system possesses many advantages over the hard disk drive and the floppy disk drive. The typical flash memory system has no moving parts, accounting for the higher reliability of the typical flash memory system. In addition, the rugged design of the typical flash memory system withstands environmental conditions and physical mishandling that would otherwise be catastrophic to the hard disk drive or the floppy disk drive. Generally, a user can access data stored in the typical flash memory system fairly quickly. Most significantly, the power consumption of the typical flash memory system is considerably lower than the hard disk drive's and the floppy disk drive's power consumption.
Although the typical flash memory system is ideally suited for mass storage applications, several properties associatedwith flash memory technology prevent the typical flash memory system from exactly replicating a data storage procedure implemented by the hard disk drive and the floppy disk drive. Maintaining compatibility with the data storage procedure implemented by the hard disk drive and the floppy disk drive is essential to the market success of the typical flash memory system because existing operating systems and existing application software are configured to operate with the data storage procedure implemented by the hard disk drive and the floppy disk drive.
One unique property of flash memory technology lies in the tendency of the typical flash memory cell to wear-out. This wearing-out property makes the typical flash memory cell unusable after a finite number of erase-write cycles. The data storage procedure implemented by the typical flash memory system must deal effectively with this finite life span of the typical flash memory cell.
Another unique property of flash memory technology is the inability to program the typical flash memory cell, if the typical flash memory cell is currently storing a particular logic state, without first performing the erase operation to erase the particular logic state before performing the write operation. Old data stored in the typical flash memory cell must be erased before attempting to program/write new data into the typical flash memory cell. Further limiting the performance of the typical flash memory system is the reality that the erase operation is a very time consuming operation relative to either the write operation or the read operation. Not only does the erase operation entail erasing the typical flash memory cell but additionally can results in the overerasure of the typical flash memory cell.
The data storage procedure implemented by the typical flash memory system minimizes the degradation in system performance associated with simply replicating the data storage procedure implemented by the hard disk drive and the floppy disk drive. The typical flash memory system endeavors to avoid writing the new data, or current version of data, in the typical flash memory cell storing the old data, or old version of the data, whenever possible to avoid performing the erase operation, unlike the hard disk drive and the floppy disk drive where the new data, or the current version of the data, is routinely programmed/written in a memory cell storing the old data, or the old version of the data. By writing the new data in an empty flash memory cell and by designating the typical flash memory cell which stores the old data as requiring the erase operation at a future convenient time, the typical flash memory system avoids performing the erase operation now, thus enhancing system performance. Additionally, to prevent certain typical flash memory cells from wearing-out and becoming unusable sooner than other typical flash memory cells, the typical flash memory system incorporates a wear leveling feature to regulate the usage—the number of erase-write cycles—of the typical flash memory cells such that all storage regions of the typical flash memory system wear-out at a fairly consistent rate. The hard disk drive and the floppy disk drive do not require this wear leveling feature because their storage mechanisms can undergo a practically unlimited number of program/write operations without impacting performance.
The typical flash memory system comprises at least one typical flash memory device.
FIG. 1
illustrates the arrangement of the typical flash memory cells in the typical flash memory device. A flash memory array
100
comprising typical flash memory cells functions as a nonvolatile mass memory component of the typical flash memory device. The flash memory array
100
is divided into a plurality of data blocks
102
, . . . ,
106
for storing data. The data blocks
102
, . . . ,
106
are conventionally labeled from zero to M−1, where M is the total number of data blocks
102
. . . ,
106
. Each data block
102
, . . . ,
106
is uniquely assigned a virtual physical block address (VPBA), the VPBA representing the typical flash memory system's method of identifying and addressing the data blocks
102
, . . . ,
106
inside the typical flash memory device. Usually, each data block
102
, . . . ,
106
is selectively programmable and erasable. Furthermore, each data block
102
, . . . ,
106
includes a plurality of sectors
112
, . . . ,
136
. Within each data block
102
, . . . ,
106
, the sectors
112
, . . . ,
136
are conventionally labeled from zero to N−1, where N is the number of sectors within each data block
102
, . . . ,
106
. Since the data blocks
102
, . . . ,
106
comprise typical flash memory cells, the data blocks
102
, . . . ,
106
are nonvolatile, i.e., the data stored in the data blocks
102
, . . . ,
106
is retained even when power is cut off.
FIG. 2
illustrates the features of the sector
200
found in each data block. Typically, the sector
200
includes a plurality of fields
202
, . . . ,
212
. A DATA field
202
is utilized for storing user data. Although the size of the DATA field
202
is typically five hundred twelve bytes which corresponds with a storage sector length in a commercially available hard disk drive or floppy disk drive, the DATA field
202
can be conf
Gossage Glenn
Haverstock & Owens LLP
Lexar Media, Inc.
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