JP2005092677A - Memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem with a memory card equipped with an NAND-type flash memory wherein its slow speed of writing into an FAT area causes a decrease in the average writing rate of a memory card. <P>SOLUTION: Data written in the FAT area are often small in volume. In an area where such a small volume of data are written, a flash memory 61 with a small block size is used. In an area where a large volume of data are written, flash memories 62-64 with a large block size are used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a memory device equipped with a plurality of rewritable nonvolatile memories.

  In recent years, memory cards equipped with a rewritable nonvolatile memory have become widespread as storage devices for storing digital information. Since memory cards are small and have excellent earthquake resistance, they are expected to be increasingly used in portable devices in the future.

  As a typical rewritable nonvolatile semiconductor memory, there is a NAND flash memory. Since NAND-type flash memory reads and writes data in units of blocks, it is not good at writing small amounts of data. For example, when writing data having a capacity smaller than the block size, it is necessary to read the already written data, replace the data, and then write again in block units.

  When the flash memory is used under the control of the disk operating system, a format similar to the format applied to the flexible disk is used. In this format, the storage area of the flash memory is divided into a boot area, a FAT (file allocation table) area, a directory area, and a data area. The data area is theoretically divided into a plurality of clusters according to the definition stored in the boot area, and files stored in the flash memory are handled in units of clusters.

  However, in the conventional flash memory format, the positions of clusters and blocks do not match. In this case, if you try to update the data (file) stored in a certain cluster, even the data that does not need to be updated will be erased together in units of blocks. It was necessary to evacuate to the cluster. Similar problems occur when data is written to the flash memory.

In order to solve such a problem, there is a method described in Patent Document 1. This is a block erasure type storage medium composed of a plurality of flocks and capable of erasing stored data in a block unit, and this block erasure type storage medium is an integer number of blocks and a data recording unit. Format information that substantially matches the cluster is created, and a format information storage area that stores the format information is provided.
JP-A-11-53248

  In the method of Patent Document 1, a plurality of storage areas having a storage capacity of 1 byte are provided in a memory cell array in a flash memory, and each storage area is arranged in a matrix of 16384 rows and 528 columns, for example. Each row of the cell array constitutes a page having a storage capacity of 528 bytes. Each page is continuously given a page address from 1 to 16384, and each storage area included in each page is given a column address from 1 to 528 continuously. Each page is configured as one block in units of 16 pages from the top.

  However, NAND flash memories used in memory cards tend to have a large block size in recent years, and there is a problem that writing data with a small capacity is relatively slow. However, data written to an area for storing a file system (hereinafter referred to as a FAT area) is generally small-capacity data in comparison with other data, and the writing speed to the FAT area is often slow. It was a factor that lowered the average writing speed of the card.

  An object of the present invention is to improve the access speed of the entire memory card by increasing the writing speed and reading speed of data in the FAT area.

  According to the first aspect of the present invention, a first memory means for writing and reading a small amount of data, a second memory means for writing and reading a large amount of data, and the first and second Control using the entire address space of the memory means as one address space, storing data in the head address area in at least a part of the first memory means, and storing data in other areas in the second memory means And a control means for performing the above.

  According to a second aspect of the present invention, in the memory device according to the first aspect, the head address area of the address space is used as an area for recording a file system.

  The invention of claim 3 of the present application is characterized in that, in the memory device of claim 1 or 2, the first memory means and the second memory means are rewritable nonvolatile semiconductor memories.

  According to a fourth aspect of the present invention, in the memory device according to the first or second aspect, the first memory means and the second memory means are a memory card on which a rewritable nonvolatile semiconductor memory is mounted. It is characterized by.

  According to the present invention, the first memory means having a high writing speed is used for small-capacity data and the second memory means is used for large-capacity data. Can be raised.

(Embodiment 1)
Hereinafter, the memory device according to Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram of a memory device according to the present embodiment. The memory device 1 is a memory card used by being mounted on an electronic device such as a digital still camera or a personal computer. The memory device 1 includes a host interface 2, a card controller 3, a buffer memory 4, a flash memory controller 5, and a plurality of flash memories 61, 62, 63, 64, and 65.

  The host interface 2 is a block that performs an interface with an electronic device main body (hereinafter referred to as a host) to which the memory device 1 is mounted. The card controller 3 is a block that controls the entire memory card 1. The buffer memory 4 is a memory that temporarily holds data transferred from the host. The flash memory controller 5 is a block that selects a flash memory to be described later and writes or reads data. The flash memories 61 to 64 are nonvolatile semiconductor memories for writing data transferred from the host.

  As shown in FIG. 2, the flash memories 61 to 64 constitute one address space, and in the present embodiment, the FAT area is arranged in an area having a small address number. For this reason, the first flash memory 61 is called a first memory means, and a flash memory having a small block size is used. The second to fourth flash memories 62, 63, 64 are called second memory means and use flash memories having a large block size. The entire address space of the first and second memory means is used as one address space.

  Data write processing of the memory device 1 configured as described above will be described. When the card controller 3 receives a write command from the host via the host interface 2, the card controller 3 temporarily holds the data sent from the host in the buffer memory 4 and transfers the data to the flash memory controller 5 in units of blocks. I do. The flash memory controller 5 selects a flash memory to be written from the flash memories 61 to 64 based on the data write address, and performs data transfer and data write. For example, if the write address is an address in the FAT area, the first flash memory 61 is selected and data is written to a predetermined address.

  As described above, a flash memory having a small block size is used for an area where a small amount of data is written, and a flash memory having a large block size is used for an area where a large amount of data is written. As a result, the writing speed of the memory card can be improved.

  In the above embodiment, the first flash memory is a NAND flash memory having a small block size, but may be a flash memory having a different method, for example, a NOR flash memory having a small block size.

(Embodiment 2)
Next, a memory device according to Embodiment 2 of the present invention will be described with reference to FIGS. FIG. 3 is a configuration diagram of the memory device 7 according to the second embodiment of the present invention. 3, blocks having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG. The memory card controller 8 is a controller that controls first to fourth memory cards 91 to 94 described later. The first to fourth memory cards 91 to 94 are nonvolatile memory cards for writing data transferred from the host. As shown in FIG. 4, the memory cards 91 to 94 constitute one address space, and in the present embodiment, the FAT area is arranged in an area having a small address number. The first memory card 91 is referred to as first memory means, and uses a memory card with a high access speed for small-capacity data. The second to fourth memory cards 92, 93, and 94 are called second memory means, and use memory cards having a high access speed for large-capacity data.

  Data write processing of the memory device 7 configured as described above will be described. When the card controller 3 receives a write command from the host via the host interface 2, the card controller 3 temporarily holds the data sent from the host in the buffer memory 4 and transfers the data to the memory card controller 8 in units of blocks. I do. The memory card controller 8 selects a memory card to be written from the first to fourth memory cards 91 to 94, based on the data write address, and transfers data and writes data. For example, if the write address is an address in the FAT area, the first memory card 91 is selected and data is written to a predetermined address.

  As described above, a memory card having a high writing speed for small-capacity data is used in the FAT area in which small-capacity data is written. In the normal data area, a memory card having a high writing speed for large-capacity data is used. By doing so, it is possible to improve the writing speed of the memory device. Further, by using a memory card as a memory for holding data, each memory portion can be easily replaced. For example, it is possible to easily increase the speed of the memory device by replacing the memory card that records the FAT area with a memory card that can write a smaller amount of data at a higher speed. Further, it is possible to easily increase the capacity of the memory device by replacing each memory card with a memory card having a large capacity.

  In the second embodiment, the first to fourth memory cards 91 to 94 do not have to be the same type of memory card. For example, a Compact Flash (registered trademark) card and an SD memory card may be mixed. .

  In the first embodiment, the FAT area and the data area are mixedly recorded in the first flash memory. In the second embodiment, the FAT area and the data area are mixedly recorded on the first memory card. However, only the FAT area may be recorded.

  In the second embodiment, the case where the present invention is applied to a memory card equipped with a non-volatile memory has been described. However, the present invention can be similarly applied to, for example, a memory built in a computer.

  Such a memory device can be suitably used for portable devices such as mobile servers, notebook PCs, and various PDAs that access frequently accessed data and large-capacity content data from a semiconductor memory.

1 is a configuration diagram of a memory device according to a first embodiment of the present invention. 4 is an explanatory diagram showing an address space of a flash memory used in the first embodiment. FIG. It is a block diagram of the memory device in Embodiment 2 of the present invention. 6 is an explanatory diagram showing an address space of a memory card used in Embodiment 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,7 Memory device 2 Host interface 3 Controller 4 Buffer memory 5 Flash memory controller 6 Flash memory 8 Memory card controller 61 1st flash memory 62 2nd flash memory 63 3rd flash memory 64 4th flash memory 91 1st 1 memory card 92 2nd memory card 93 3rd memory card 94 4th memory card

Claims (4)

First memory means for writing and reading a small amount of data;
A second memory means for writing and reading a large amount of data;
The entire address space of the first and second memory means is used as one address space, data in the head address area is stored in at least a part of the first memory means, and data in other areas is stored in the second area. Control means for performing control to be stored in the memory means.   2. The memory device according to claim 1, wherein the head address area of the address space is used as an area for recording a file system.   3. The memory device according to claim 1, wherein the first memory means and the second memory means are rewritable nonvolatile semiconductor memories. 3. The memory device according to claim 1, wherein the first memory means and the second memory means are memory cards equipped with a rewritable nonvolatile semiconductor memory.

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