Nonvolatile memory with cluster-erase flash capability and solid state file apparatus using the same

• US 5,598,370 A
• Filed: 04/26/1995
• Issued: 01/28/1997
• Est. Priority Date: 02/24/1993
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Asano, Hideo, Toyooka, Takashi, Niijima, Hideto, Sakaue, Yoshinori
• Primary Examiner(s): Fears, Terrell W.
• Application Number:
  US08/429,395
• Time in Patent Office: 643 Days
• Field of Search: 365/185.33, 365/218
• US Class Current: 365/185.33
• 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 2212/7209 Validity control, e.g. using flags, time stamps or sequence numbers
• 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 16/102 External programming circuits, e.g. EPROM programmers; In-circuit programming or reprogramming; EPROM emulators

Abstract

A nonvolatile memory-with cluster-erase flash capability. A cluster information sector is included in each of N clusters, the cluster information sector of each cluster being written with the sequence number assigned to the cluster so that no two clusters have the same sequence number. When erasing a given sector, a controller saves its sequence number prior to erasure. Then, when initializing a given erased sector, the controller sets its sequence number to a value greater than the current maximum sequence number. The controller writes user data to sectors other than the cluster information sector for the cluster thus initialized according to their address sequence. Accordingly, an invalid sector can be distinguished from a valid sector without using an overwrite approach.

Claims

1. A nonvolatile memory for cluster-erase flash, comprising:

a flash memory having N clusters each having M sectors, wherein M and N are integers greater than one;

each of said N clusters includes a cluster information sector, wherein one of said M sectors is said cluster information sector;

and said cluster information sector of each of said N clusters holds a sequence number, wherein no two of said cluster information sectors have the same sequence number.

2. The nonvolatile memory as claimed in claim 1, wherein said cluster information sector of each of said N clusters holds a cluster erase count, the sum of the cluster erase counts being equal to a maximum value of the sequence numbers.

6. The nonvolatile memory of claim 1 wherein each of said cluster information sectors further comprises:

a cluster erase count; and

an attribute flag within said each cluster information sector for identifying each of said cluster information sectors as a cluster information sector.

10. The nonvolatile memory of claim 1 wherein the nonvolatile memory comprises a NAND-type flash EEPROM.

3. A method for storing data within a nonvolatile memory for cluster-erase flash, wherein the nonvolatile memory comprises a flash memory having N clusters each having M sectors, wherein M and N are integers greater than one and each of said N clusters includes a cluster information sector, wherein one of said M sectors is said cluster information sector, wherein said cluster information sector of each of said N clusters holds a sequence number, wherein no two of said cluster information sectors have the same sequence number and there being a maximum sequence number, and comprising the steps of:

selecting a cluster to be written based on a cluster erase count contained in the cluster information sector; and

writing data sequentially to the sectors within the selected cluster.

4. The method of claim 3 wherein the sum of said erase counts for all said N clusters equals said maximum sequence number.

5. The method of claim 3 wherein said flash memory is a NAND-type flash EEPROM.

7. A nonvolatile NAND-type flash EEPROM memory for cluster-erase flash, comprising:

a flash memory having N clusters, each cluster having M sectors, wherein M and N are integers greater than one and wherein at least one of said M sectors is a data sector;

each of said N clusters includes a cluster information sector wherein one of said M sectors is the cluster information sector;

said cluster information sector of each of said N clusters holds a sequence number, wherein no two of the cluster information sectors have the same sequence number and there being a maximum sequence number.

8. The nonvolatile memory of claim 7 wherein the sum of the cluster erase counts is equal to said maximum sequence number.

9. The nonvolatile memory of claim 7 wherein each of said data sectors further comprises an attribute flag which identifies said data sector as a data sector.