Block-erasable non-volatile semiconductor memory which tracks and stores the total number of write/erase cycles for each block

• US 5,544,356 A
• Filed: 03/03/1995
• Issued: 08/06/1996
• Est. Priority Date: 12/31/1990
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Robinson, Kurt B., Levy, Markus A., Elbert, Dale K.
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): Lintz, Paul R.
• Application Number:
  US08/400,272
• Time in Patent Office: 522 Days
• Field of Search: 395/425, 395/600, 395/430, 395/182.03, 365/185, 365/218, 365/230.03, 365/900, 365/185.11
• US Class Current: 707/821
• CPC Class Codes: G06F 12/023 Free address space management
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 12/0638 Combination of memories, e.g. ROM and RAM such as to permit replacement or supplementing of words in one module by words in another module address formation of the next microinstruction G06F9/26; masking faults in memories by using spares or by reconfiguring G11C29/70
• CPC Class Codes: G06F 2212/7211 Wear leveling
• CPC Class Codes: G06F 3/0601 Interfaces specially adapted for storage systems
• CPC Class Codes: G06F 3/0664 at device level, e.g. emulation of a storage device or system
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles

Abstract

A non-volatile semiconductor memory that is erasable only in blocks is described. Each bit of the non-volatile semiconductor memory cannot be overwritten from a first logical state to a second logical state without a prior erasure. Each bit of the non-volatile semiconductor memory can be overwritten from a second logical state to a first logical state without a prior erasure. The non-volatile semiconductor memory comprises an active block for storing a first file, a reserve block for storing a second file, and a directory block. The second file is a copy of the first file. The copy is made during a clean-up operation prior to erasure of the active block. The directory block comprises a directory entry for identifying the first file.

Claims

1. A processor-controlled method of file management for a nonvolatile semiconductor memory with a plurality of physical erase blocks, wherein bits of the memory cannot be overwritten from a first logical state to a second logical state without a prior erasure, wherein erasure is by physical erase block and not on an individual byte basis, the method comprising the steps of:

(1) allocating a first physical erase block of the memory for storing an active file and a deleted file;

(2) allocating a second physical erase block of the memory for storing a copy of the active file;

(3) storing in an allocated first portion of a third physical erase block of the memory information as to whether a physical erase block of the memory has been allocated to store the active and deleted files or allocated to store the copy of the active file;

(4) reclaiming memory space by storing in the second physical erase block of the memory the copy of the active file and by erasing the entire first physical erase block of the memory in order to permit reuse of the first physical erase block of the memory for storage;

(5) tracking a number of times a physical erase block of the memory has been cycled and storing that number as a cycle count in an allocated second portion of the third physical erase block of the memory;

(6) storing in an allocated third portion of the third physical erase block of the memory a directory of active files;

(7) minimizing cycling distributions between physical erase blocks of the memory by choosing for reclamation a physical erase block of the memory with a lowest cycle count.

2. The processor-controlled method of claim 1, further comprising the steps of storing in an allocated fourth portion of the third physical erase block of the memory (1) an indication as to whether a physical erase block of the memory is in use or not and (2) and indication as to whether a physical erase block of the memory is defective or not.

3. The processor-controlled method of claim 1, further comprising the step of storing in an allocated fourth portion of the third physical erase block of the memory information concerning a file structure of the memory.

4. The processor-controlled method of claim 3, wherein the information stored in the fourth portion of the third physical erase block of the memory comprises

(i) information concerning a file structure type of the memory;

(ii) information that defines a formattable capacity of the file structure;

(iii) information concerning the directory of active files.

5. The processor-controlled method of claim 1, wherein the directory of active files comprises a linked list.

6. The processor-controlled method of claim 3, wherein the file structure is a variable-length file structure.

7. The processor-controlled method of claim 3, wherein the file structure is a sectored file structure.

8. The processor-controlled method of claim 1, further comprising the step of storing information in an allocated fourth portion of the third physical erase block of the memory that indicates a maximum number of erase cycles recommended for the memory.

9. A processor-controlled method of file management for a nonvolatile semiconductor first memory with a plurality of physical erase blocks, wherein bits of the first memory cannot be overwritten from a first logical state to a second logical state without a prior erasure, wherein erasure is by physical erase block and not on an individual byte basis, the method comprising the steps of:

(1) allocating a first physical erase block of the first memory for storing an active file and a deleted file;

(2) allocating a second physical erase block of the first memory for storing a copy of the active file;

(3) storing in an allocated first portion of a second memory information as to whether a physical erase block of the first memory has been allocated to store the active and deleted files or allocated to store the copy of the active file;

(4) reclaiming memory space of the first memory by storing in the second physical erase block of the first memory the copy of the active file and by erasing the entire first physical erase block of the first memory in order to permit reuse of the first physical erase block of the first memory for storage;

(5) tracking a number of times a physical erase block of the first memory has been cycled and storing that number as a cycle count in an allocated second portion of the second memory;

(6) storing in an allocated third portion of the second memory a directory of active files;

(7) minimizing cycling distributions between physical erase blocks of the first memory by choosing for reclamation a physical erase block of the first memory with a lowest cycle count.

10. The processor-controlled method of claim 9, further comprising the step of storing in an allocated fourth portion of the second memory (1) an indication as to whether a physical erase block of the first memory is in use or not and (2) an indication as to whether a physical erase block of the first memory is defective or not.

11. The processor-controlled method of claim 9, further comprising the step of storing in an allocated fourth portion of the second memory information concerning a file structure of the first memory.

12. The processor-controlled method of claim 11, wherein the information stored in the fourth portion of the second memory comprises

(i) information concerning a file structure type of the first memory;

(ii) information that defines a formattable capacity of the file structure;

(iii) information concerning the directory of active files.

13. The processor-controlled method of claim 9, wherein the directory of active files comprises a linked list.

14. The processor-controlled method of claim 9, wherein the directory of active files is an alterable hierarchical directory.

15. The processor-controlled method of claim 11, wherein the file structure is a variable-length file structure.

16. The processor-controlled method of claim 11, wherein the file structure is a sectored file structure.

17. The processor-controlled method of claim 9, wherein the second memory is a byte-alterable electrically erasable programmable read-only memory.

18. The processor-controlled method of claim 9, wherein the second memory is a random-access memory.

19. The processor-controlled method of claim 9, further comprising the step of storing information in an allocated fourth portion of the second memory that indicates a maximum number of erase cycles recommended for the first memory.

20. A processor-controlled method of file management for a nonvolatile semiconductor memory with a plurality of physical erase blocks, wherein bits of the memory cannot be overwritten from a first logical state to a second logical state without a prior erasure, wherein erasure is by physical erase block and not on an individual byte basis, the method comprising the steps of:

(1) allocating a first sector of a first physical erase block of the memory for storing an active file and a second sector of the first physical erase block for storing a deleted file;

(2) allocating a first sector of a second physical erase block of the memory for storing a copy of the active file;

(3) storing in a first portion of an allocated third physical erase block of the memory information as to whether a sector of a physical erase block of the memory has been allocated to store one of the active and deleted files or allocated to store the copy of the active file;

(4) reclaiming memory space by storing in the first sector of the second physical erase block of the memory the copy of the active file and by erasing the entire first physical erase block of the memory in order to permit reuse of the first physical erase block of the memory for storage;

(5) tracking a number of time a physical erase block of the memory has been cycled and storing that number as a cycle count in a second portion of the allocated third physical erase block of the memory;

(6) storing in a third portion of the allocated third physical erase block of the memory a directory of active files;

(7) minimizing cycling distributions between physical erase blocks of the memory by choosing for reclamation a physical erase block of the memory with a lowest cycle court.

21. The processor-controlled method of claim 20, further comprising the step of storing in a fourth portion of the allocated third physical erase block of the memory (1) an indication as to whether a physical erase block of the memory is in use or not and (2) an indication as to whether a physical erase block of the memory is defective or not.

22. The processor-controlled method of claim 20, further comprising the step of storing in a fourth portion of the allocated third physical erase block of the memory information concerning a file structure of the memory.

23. The processor-controlled method of claim 20, wherein the directory of active files comprises a linked list.

24. The processor-controlled method of claim 20, further comprising the step of storing information in an allocated fourth portion of the third physical erase block that indicates a maximum number of erase cycles recommended for the memory.

25. A processor-controlled method of file management for a nonvolatile semiconductor first memory with a plurality of physical erase blocks, wherein bits of the memory cannot be overwritten from a first logical state to a second logical state without a prior erasure, wherein erasure is by physical erase block and not on an individual byte basis, the method comprising the steps of:

(1) allocating a first sector of a first physical erase block of the first memory for storing an active file and a second sector of the first physical erase block for storing a deleted file;

(2) allocating a first sector of a second physical erase block of the first memory for storing a copy of the active file;

(3) storing in an allocated first portion of a second memory separate from the first memory information as to whether a sector of a physical erase block of the memory has been allocated to store one of the active and deleted files or allocated to store the copy of the active file;

(4) cleaning up the first memory by storing in the first sector of the second physical erase block of the first memory the copy of the active file and by erasing the entire first physical erase block of the first memory in order to permit reuse of the first physical erase block of the first memory for storage;

(5) tracking a number of times a physical erase block of the first memory has been cycled and storing that number as a cycle count in an allocated second portion of the second memory;

(6) storing in a allocated third portion of the second memory a directory of active files;

(7) minimizing cycling distributions between physical erase blocks of the first memory by choosing for reclamation a physical erase block of the first memory with a lowest cycle count.

26. The processor-controlled method of claim 25, further comprising the step of storing in an allocated fourth portion of the second memory (1) an indication as to whether a physical erase block of the memory is in use or not and (2) an indication as to whether a physical erase block of the memory is defective or not.

27. The processor-controlled method of claim 25, further comprising the step of storing in an allocated fourth portion of the second memory information concerning a file structure of the first memory.

28. The processor-controlled method of claim 25, wherein the directory of active files comprises a linked list.

29. The processor-controlled method of claim 25, wherein the directory of active files is an alterable hierarchical directory.

30. The processor-controlled method of claim 25, wherein the second memory is a byte-alterable electrically erasable programmable read-only memory.

31. The processor-controlled method of claim 25, wherein the second memory is a random-access memory.

32. The processor-controlled method of claim 25, further comprising the step of storing information in an allocated fourth portion of the second memory that indicates a maximum number of erase cycles recommended for the first memory.

33. A processor-controlled method of file management for a nonvolatile semiconductor memory with a plurality of physical erase blocks, wherein bits of the memory cannot be overwritten from a first logical state to a second logical state without a prior erasure, wherein erasure is by physical erase block and not on an individual byte basis, the method comprising the steps of:

(1) allocating a first portion of the memory in a first physical erase block for storing an active file and a deleted file;

(2) allocating a second portion of the memory in a second physical erase block for storing a copy of the active file;

(3) storing in an allocated third portion of the memory information as to whether a portion of the memory has been allocated to store the active and deleted files or allocated to store the copy of the active file;

(4) reclaiming memory space by storing in the second portion of the memory the copy of the active file and by erasing the first physical erase block including the first portion of the memory in order to permit reuse of the first portion of the memory for storage;

(5) tracking a number of times a portion of the memory has been cycled and storing the number as a cycle count in an allocated fourth portion of the memory;

(6) minimizing cycling distributions between physical erase blocks of the memory by choosing for reclamation a portion of the memory with a lowest cycle count.