Direct logical block addressing flash memory mass storage architecture

• US 5,845,313 A
• Filed: 07/31/1995
• Issued: 12/01/1998
• Est. Priority Date: 07/31/1995
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Lexar
• Inventors: Estakhri, Petro, Assar, Mahmud
• Primary Examiner(s): Chan, Eddie P.
• Assistant Examiner(s): BRAGDON, REGINALD GLENWOOD
• Application Number:
  US08/509,706
• Time in Patent Office: 1,219 Days
• Field of Search: 395/430, 395/431, 395/435, 395/483, 395/413, 711/103, 711/104, 711/108, 711/156, 711/203
• US Class Current: 711/103
• CPC Class Codes: G06F 11/1068 in sector programmable memories, e.g. flash disk G06F11/1072 takes precedence
• 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 3/0613 in relation to throughput
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/064 Management of blocks
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: G11C 16/08 Address circuits; Decoders; Word-line control circuits
• CPC Class Codes: G11C 16/102 External programming circuits, e.g. EPROM programmers; In-circuit programming or reprogramming; EPROM emulators
• CPC Class Codes: G11C 29/765 in solid state disks
• CPC Class Codes: G11C 29/82 for EEPROMs

Abstract

A nonvolatile semiconductor mass storage system and architecture can be substituted for a rotating hard disk. The system and architecture avoid erase cycles each time information stored in the mass storage is changed. Erase cycle are avoided by programming an altered data file into an empty mass storage block rather than over itself as a hard disk would. Periodically, the mass storage will need to be cleaned up. These advantages are achieved through the use of several flags, and a map to correlate a logical block address of a block to a physical address of that block. In particular, flags are provided for defective blocks, used blocks, and old versions of a block. An array of volatile memory is addressable according to the logical address and stores the physical address

Claims

1. A mass storage device having nonvolatile memory, the storage device being coupled to an external digital system for storing binary information therefor in the nonvolatile memory, the external digital system including means for generating a plurality of logical block addresses for use in storing or reading data, the storage device comprising:

a. a volatile memory device having a plurality of volatile memory locations each of which is uniquely addressable by one of the logical block addresses, and wherein each of the volatile memory locations is configured to store a physical block address without requiring the storage of a corresponding logical block address;

b. one or more nonvolatile memory devices each having a plurality of nonvolatile data blocks, wherein each block is selectively programmable and erasable and further wherein each data block is uniquely addressable by one of the physical block addresses, and further wherein the plurality of nonvolatile data blocks has a plurality of used/free flags, one stored with each data block in the one or more nonvolatile memory devices for indicating whether a data block contains data; and

c. a controller for receiving a block of data from the external digital system to be stored in the one or more nonvolatile memory devices, for receiving a target logical block address from the external system, for identifying a free data block within the nonvolatile data blocks having no data stored therein, for storing the physical block address of the free data block in the volatile memory location that corresponds to the target logical block address, and for periodically erasing all data blocks of the nonvolatile memory devices having flags which are set, whereby an erase cycle is not needed each time the external system writes to the storage device;

wherein the used/free flags stored in the one or more nonvolatile memory devices which correlate to the physical block addresses of the plurality of nonvolatile data blocks are copied to the volatile memory locations during a power-up and a system reset.

2. The device according to claim 1 further comprising means for addressing one of the plurality of volatile memory locations using a desired logical block address, means for retrieving a physical block address stored in the volatile memory location that corresponds to the desired logical block address, means for reading a data block within the nonvolatile memory devices identified by the retrieved physical block address and means for coupling the data block read from the nonvolatile memory device to the external system.

3. The device according to claim 2 further comprising a plurality of old/new flags, one stored with each data block in the one or more nonvolatile memory devices, for indicating whether the data block contains data that has been superseded.

4. The device of claim 3, wherein the old/new flags stored in the one or more nonvolatile memory devices which correlate to the physical block addresses of the plurality of nonvolatile data blocks are copied to the volatile memory locations during a power-up and a system reset.

5. The device according to claim 4 wherein each logical block address is also stored with one of the data blocks in the one or more nonvolatile memory devices.

6. The device according to claim 5 wherein the logical block addresses in the one or more nonvolatile memory devices which correlate to the physical block addresses of the plurality of nonvolatile data blocks are utilized in copying the used/free flags and the old/new flags to the volatile memory locations during a power-up and a system reset.

7. The device according to claim 1 wherein the flags which are set include old/new flags which are set.

8. The device according to claim 1 wherein the volatile memory comprise RAM cells.