External information storage system with a semiconductor memory

• US 5,524,230 A
• Filed: 03/27/1995
• Issued: 06/04/1996
• Est. Priority Date: 07/12/1991
• Status: Expired due to Fees

• Current Assignee: International Business Machines Incorporated (International Business Machines Corporation)
• Original Assignee: International Business Machines Incorporated (International Business Machines Corporation)
• Inventors: Niijima, Hideto, Sakaue, Yoshinori
• Primary Examiner(s): Chan, Eddie P.
• Assistant Examiner(s): Asta, Frank J.
• Application Number:
  US08/410,589
• Time in Patent Office: 435 Days
• Field of Search: 395/400, 395/425, 364/966.4, 364/965.76, 364/200 MS File, 364/900 MS File
• US Class Current: 711/103
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 12/122 of the least frequently used [LFU] type, e.g. with individual count value
• CPC Class Codes: G06F 2212/2022 Flash memory
• CPC Class Codes: G06F 2212/312 In storage controller
• 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
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles

Abstract

To provide an external storage system using a semiconductor memory in which the data reading and writing between the host CPU can be processed faster than the conventional magnetic disk, and only a particular sector is not frequently written and erased so that the whole memory is effectively used over a long period of time. An address control scheme was introduced in which flexibility is given to the address relation between the host CPU and the external storage and the physical address of the semiconductor memory is not one-sidedly determined by the logical address possessed by the command of the host CPU. Command processing section 34 always prepares memory blocks and sectors for writing or erasing and copying in preparation for the command processing of the host CPU, and records and holds the correspondence relation between the physical address of the selected memory block 32i or sector and the command of the host CPU in address conversion table 36. The status of memory blocks and sectors is recorded in respective managing tables 35 and 60, and used for control of processings such as writing, erasing and copying in preparation for or in response to the command of the host CPU.

Claims

1. A method of controlling an external storage system comprising a semiconductor memory as an external storage device, the external storage device further comprising a flash memory having a plurality of memory blocks each memory including at least one sector, and a control section, including a block managing unit for performing control over said memory blocks, and for maintaining a record of the number of times each memory block has been erase and the status of each memory block and sector, the external storage system being connected to a host processor through a bus for transferring data and a command, the method comprising the steps of:

selecting, under control of the control section, a memory block for which data is written or erased on the basis of the record of the block managing unit,

converting a logical address included in a command of the host processor to a physical address indicating a corresponding sector in a particular memory block, responding to one of three different commands to perform a process of data writing or reading to the corresponding sector or memory block erasure,

sequentially updating the status changes of each sector and memory block resulting from the processes in the block managing means, and

recording and updating the relationships between the physical addresses and the logical addresses of the memory block and sector on which the processes were performed in the address conversion means.

2. A method for controlling an external storage system as in claim 1 further comprising the steps of:

accepting a command from the host processor by interruption, and

if the command is a data read command, responding thereto to perform the process of reading the data from the corresponding sector of the memory block corresponding to the logical address of the command, and

if the command is a write or erase command, holding such command

and data in a buffer and executing the write or erase process to the selected memory block or sector when there is no interrupt command from the host processor.

3. A method for controlling an external storage system as in claim 1 further comprising the step of:

selecting, with the control section, a memory block in which data writing or erasing is to be executed on the basis of the record of the block managing unit.

4. A method for controlling an external storage system as in claim 1 further comprising the steps of:

selecting with the control section, based on the record of the block control unit, a memory block having free sectors for copying the data in valid sectors of the memory block to be erased, and

copying the data into the selected memory block prior to the erasure of the memory block.

5. A method for controlling a computer system comprising a host processor, a semiconductor memory used as an external storage device, the external memory further comprising a flash memory having a plurality of memory blocks each including at least one sector, and a control section including a block managing unit for performing control over memory blocks, and for maintaining a record of the number of times each memory block has been erased and the status of each memory block and sector, the method comprising the steps of:

converting, under control of the control section the logical address included in the command of the host processor to a physical address indicating the sector in a particular memory block by an address conversion means,

selecting a memory block for data writing and a memory block to be erased next to acquire the memory block for data writing, respectively, on the basis of the record of block managing means which has sequentially recorded therein the number of times each memory block was erased and the status of each sector and memory block,

writing the data to be written received from the host processor into the memory block for writing,

erasing the selected memory block for erasure, and

executing a process of data writing, reading or erasing to the memory block or sector that has the physical address obtained from an address conversion table in response to the command.

6. A method as in claim 5, further comprising the step of:

selecting, under control of the control section, a particular memory block of the memory blocks with priority as a memory block to be erased if the number of times the particular memory block was erased is smaller than the largest number of times and other memory block was erased by a predetermined value.

7. A method as in claim 5 further comprising the steps of:

accepting by the control section a command of the host processor by interruption, and if said command is a data read command, reading the data from the corresponding sector of the memory block corresponding to the logical address, and

if the command is a write or erase command, holding the command and data in a buffer and executing write or erase processes to the corresponding memory block or sector when there is no interrupt command from the host processor.

8. A method as in claim 5 further comprising the step of:

responding with the control section to a sector write command from the host processor to write the data into a free sector of the selected memory block, and if the logical address of the sector write command is equal to the logical address of the valid sector which has already been written, rewriting only the record of the status with respect to the valid sector of the block managing means to invalid one, and writing the physical address of the free sector into the address conversion means.

9. A method as in claim 5 further comprising the step of:

updating under control of the control section the record of the block managing means on the erasure of the memory block by comparison of the new file allocation information held by the host processor with the old file allocation information held in the external storage system.

10. A method as in claim 5 further comprising the step of:

saving, under control of the control section, a record of the number of times the memory block was erased prior to the erasure of the memory block, and writing the record back to the memory block after the erasure of the memory block.

11. An external storage system connected to a host processor through a host bus for transferring data and at least one command, the storage system comprising:

a semiconductor memory comprising a flash memory having a plurality of memory blocks each including at least one sector,

address conversion means for converting a logical address received from the host processor to a physical address corresponding to a particular sector, and

block managing means for recording the status of each memory block and sector, and a control section which uses the record of the block managing means to control the reading or writing of data to each sector of the semiconductor memory, or the erasing of a memory block, said address conversion being done on the basis of the record.

12. An external storage system, as in claim 11, wherein the control section further comprises:

a command processing section,

a block managing table and an address conversion table formed on the RAM of the main memory,

a memory controller including a buffer, and

a sector managing table constituting the block managing means along with the block managing table provided on each memory block.

13. An external storage system, as in claim 11, wherein the control section further comprises a data writing section, data reading section and block erasing section for executing a data writing, reading or erasing process to the corresponding memory block or sector of the semiconductor memory on the basis of the command processing section, and a sector copying section for copying the valid sectors of the memory block to be erased to another memory block.

14. An external storage system, as in claim 11, wherein said control section further comprises:

a command processing section, data writing section, data reading section, block erasing section, and a sector copying section used for copying the valid sectors of a memory block to be erased to another memory block which consists of a microprocessor, a block managing table, address conversion table and a buffer which are formed on a RAM, and

a sector managing table comprising the block managing means along with the block managing table provided on each memory block.

15. A computer system comprising a host processor, an external storage system including a semiconductor memory which is further comprised of a flash memory having a plurality of memory blocks each including at least one sector, and a host bus for transferring data and a command between the external storage system and the host processor, characterized by:

address conversion means for converting the address from the host processor to the physical address of a particular sector and block managing means for recording the status of each memory block and each sector therein to control the data reading and writing to each sector of the semiconductor memory and the erasure of a memory block in response to the command, said address conversion being done on the basis of the status of each memory block,

the control means having means which are responsive to the command from the host processor for executing the process of data writing or reading to the corresponding sector of the semiconductor memory or of erasing a memory block, and for updating the record of the status of each memory block and each sector of the block managing means in connection with such process.

16. A computer system, as in claim 15, further comprising:

interactive display means, connected to the host processor and the external storage system through the host bus, for receiving information from a user.

17. A computer system, as in claim 15, further comprising:

display means connected to the host processor and the external storage system through the host bus, wherein

the control means outputs to the display means that the semiconducter memory is to be replaced when there is no free sector in any of the memory blocks and there is also no memory block to be erased.