Methods for overwriting data in a memory device

• US 6,647,471 B2
• Filed: 09/23/2002
• Issued: 11/11/2003
• Est. Priority Date: 09/15/2000
• Status: Expired due to Fees

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Matrix Semiconductor, Inc. (Western Digital Corporation)
• Inventors: Moore, Christopher S., Brown, Daniel T., March, Roger W.
• Primary Examiner(s): PORTKA, GARY J
• Application Number:
  US10/253,089
• Publication Number:
  US 20030028734A1
• Time in Patent Office: 414 Days
• Field of Search: 711/102, 711/103, 711/101, 711/154, 711/156, 713/200, 714/6, 714/7, 714/746
• US Class Current: 711/154
• CPC Class Codes: G06F 11/1008 in individual solid state devices G06F11/1004 takes precedence
• CPC Class Codes: G06F 2003/0697 device management, e.g. handlers, drivers, I/O schedulers
• CPC Class Codes: G06F 3/0601 Interfaces specially adapted for storage systems
• CPC Class Codes: G06F 3/0619 in relation to data integrity, e.g. data losses, bit errors
• CPC Class Codes: G06F 3/0631 by allocating resources to storage systems
• CPC Class Codes: G06F 3/0643 Management of files
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: G06F 3/08 from or to individual record carriers, e.g. punched card , memory card, integrated circuit [IC] card or smart card
• CPC Class Codes: G11C 17/00 Read-only memories programmable only once; Semi-permanent stores, e.g. manually-replaceable information cards
• CPC Class Codes: Y10S 707/99934 Query formulation, input preparation, or translation
• CPC Class Codes: Y10S 707/99943 Generating database or data structure, e.g. via user interface
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99956 File allocation

Abstract

The preferred embodiments described herein provide a memory device and methods for use therewith. In one preferred embodiment, a method is presented for using a file system to dynamically respond to variability in an indicated minimum number of memory cells of first and second write-once memory devices. In another preferred embodiment, a method for overwriting data in a memory device is described in which an error code is disregarded after a destructive pattern is written. In yet another preferred embodiment, a method is presented in which, after a block of memory has been allocated for a file to be stored in a memory device, available lines in that block are determined. Another preferred embodiment relates to reserving at least one memory cell in a memory device for file structures or file system structures. A memory device is also provided in which file system structures of at least two file systems are stored in the same memory partition. Additionally, methods for permanently preventing modification of data stored in a memory device and for identifying memory cells storing data are disclosed.

Claims

1. A method or overwriting data in a memory device comprising a first and second set of memory cells, the method comprising:

(a) storing data in a first set of memory cells in a memory device;

(b) storing an error code in a second set of memory cells in the memory device, the error code representing the data stored in the first set of memory cells;

(c) writing a destructive pattern into at least some of the first set of memory cells, wherein the error code no longer represents the data stored in the first set of memory cells after the destructive pattern is written and wherein the destructive pattern introduces an error in the data that is correctable by the error code stored in the second set of memory cells;

(d) storing a flag in a third set of memory cells in the memory device indicating that the data is deleted data;

(e) with a file system, determining whether the flag was stored in the third set of memory cells; and

(f) if the file system determines that the flag was stored in the third set of memory cells, allowing the data to remain uncorrected even though the error is correctable.

2. The method of claim 1, wherein the flag is designated in a file listing.

3. The method of claim 1, wherein the flag is stored as an entry in a table.

4. The method of claim 1, wherein the error code comprises an error checking and correcting (ECC) code.

5. The method of claim 1, wherein the memory device is logically organized into a plurality of lines, and wherein a line comprises the first and second sets of memory cells.

6. The method of claim 1, wherein the first set of memory cells comprises a minimum number of memory cells that can be written into during a write operation.

7. The method of claim 1, wherein the memory device comprises a write-once memory device.

8. The method of claim 1, wherein the memory device comprises a three-dimensional write-once memory device.

9. A method for overwriting data in a memory device comprising a first and second set of memory cells, the method comprising:

(a) storing data in a first set of memory cells in a memory device;

(b) storing an error code in a second set of memory cells in the memory device, the error code representing the data stored in the first set of memory cells;

(c) writing a destructive pattern into at least some of the first set of memory cells, wherein the error code no longer represents the data stored in the first set of memory cells after the destructive pattern is written and wherein the destructive pattern introduces an error in the data that is uncorrectable by the error code stored in the second set of memory cells;

(d) storing a flag in a third set of memory cells in the memory device indicating that the data is deleted data;

(e) obtaining an error when attempting to correct the data using the error code;

(f) with a file system, determining whether the flag was stored in the third set of memory cells; and

(g) if the file system determines that the flag was stored in the third set of memory cells, ignoring the error obtained in (e).

10. The method of claim 9 further comprising:

(h) if the file system determines that the flag was not stored in the third set of memory cells, returning the data despite the presence of the uncorrectable error.

11. The method of claim 9, wherein the flag is designated in a file listing.

12. The method of claim 9, wherein the flag is stored as an entry in a table.

13. The method of claim 9, wherein the error code comprises an error checking and correcting (ECC) code.

14. The method of claim 9, wherein the memory device is logically organized into a plurality of lines, and wherein a line comprises the first and second sets of memory cells.

15. The method of claim 9, wherein the first set of memory cells comprises a minimum number of memory cell that can be written into during a write operation.

16. The method of claim 9, wherein the memory device comprises a write-once memory device.

17. The method of claim 9, wherein the memory device comprises a three-dimensional write-once memory device.