Electrical computers and digital processing systems: memory – Storage accessing and control – Memory configuring
Reexamination Certificate
1997-05-23
2001-02-13
Peikari, B. James (Department: 2752)
Electrical computers and digital processing systems: memory
Storage accessing and control
Memory configuring
C711S172000, C711S170000, C709S241000
Reexamination Certificate
active
06189081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-volatile semiconductor storage, and more specifically to an improved method for writing and rewriting data in a non-volatile semiconductor storage.
2. Description of Related Art
In the prior art, a disk apparatus used as an external storage for a personal computer mainly includes a hard disk apparatus, a floppy disk apparatus and an optical magnetic disk apparatus. Recently, an external storage composed of a semiconductor memory has been developed. This semiconductor storage is still high in cost per a memory capacity, in comparison with the above mentioned disk apparatuses, but have various advantages that: mechanical parts are a little; it is easy to miniaturize and lighten; a moisture resistance is high; impact resistance is also high; an operation speed is high; and electric power consumption is lower. Therefore, the semiconductor storage is expected to be applied to portable or handy instruments in the form of a memory card including a plurality of semiconductor memories accommodated in a card-shaped housing.
The semiconductor memories constituting the semiconductor storage can roughly be divided into a RAM (random access memory) and ROM (read only memory). The RAM is volatile, and needs a backup power battery in order to continue to maintain stored data. Therefore, consumed electric power increases. On the other hand, the ROM is non-volatile and needs no backup power battery in order to continue to maintain stored data. Therefore, it is optimum to realize a lower electric power consumption. The ROM includes an MROM (Mask ROM), a UVEPROM (Ultra-Violet Erasable and Programmable ROM), and an EEPROM (Electrically Erasable and Programmable ROM).
Of these various types of ROM, the MROM is inexpensive, but is limited in a use extent since it is impossible to rewrite data. The UVEPROM is possible to rewrite data, but is also limited in a use extent, although it has the use extent wider than that of the MROM, since it is necessary to irradiate ultraviolet for erasure of old data prior to a data rewriting. The EEPROM is possible to rewrite data with no necessity of ultraviolet irradiation, and therefore, can be said to be optimum to a semiconductor storage disk.
The EEPROM includes a byte erasure type EEPROM configured to erase data in units of bytes, and a flash type EEPROM capable of erasing all data in the memory chip in bundle or in units of block which are larger than the bytes. This flash type EEPROM will be called simply a “flash memory” hereinafter.
The byte erasure type EEPROM needs an erasure circuit for erasing data in units of bytes, which is more complicated than that of the flash memory, and which requires circuits elements of the number larger than that required in the flash memory. In comparison with the flash memory, therefore, the byte erasure type EEPROM is not suitable in order to realize a large memory capacity of semiconductor storage disk. On the other hand, the flask memory of the type configured to erase all data in the memory chip in bundles has such a disadvantage that, a buffer memory has the same memory capacity as that of the flash memory, in order to save the data not to be rewritten when only a portion of the data is to be rewritten, and therefore, a rewriting time inevitably becomes long. Recently, under these circumstance, it is in many cases that the flash memory of the type configured to erase data in the memory chip in units of blocks, is incorporated into the semiconductor memory disk.
Now, a non-volatile semiconductor storage using the flash memory (called a “semiconductor disk” hereinafter) will be described.
Referring to
FIG. 1
, there is shown a block diagram illustrating an overall structure of a portable or handy instrument and the semiconductor disk using the flash memory. A semiconductor disk
20
is connected to a portable instrument
21
through an electrical connection means (not shown) such as an electrical connector. The portable instrument
21
includes a central processing unit (CPU)
22
, a main memory
23
and peripheral devices
25
, which are coupled in common to a bus
24
. The bus
24
is connected to the electrical connection means to the semiconductor disk
20
.
As shown in
FIG. 2
, the semiconductor disk
20
includes one or more flash memories
30
A to
30
C (which are representatively designated by Reference Numeral “
30
” in this specification), a card controller
31
for controlling all data processings between the portable instrument
21
and the semiconductor disk
20
, which are exemplified by a reading of data from the semiconductor disk
20
, a writing of data into the semiconductor disk
20
and a rewriting of data in the semiconductor disk
20
, and a buffer RAM
33
for temporarily storing the data processed between the portable instrument
21
and the semiconductor disk
20
.
In each flash memory
30
mounted on the semiconductor disk
20
, as shown in
FIG. 3
, a chip is divided into one or more blocks
40
A to
40
F (which are representatively designated by Reference Numeral “
40
” in this specification). These blocks
40
are so configured that data stored in the flash memory can be erased in units of block, under control of an overall control circuit
42
(for controlling the whole of the flash memory
30
) and block control circuits
41
A to
41
F (which are representatively designated by Reference Numeral “
41
” in this specification) which are provided for the blocks
40
A to
40
F, respectively, in a one-to-one relation. Since the overall control circuit
42
and the block control circuits
41
are well known to persons skilled in the art, explanation of a detailed control performed by these control circuits will be omitted.
In a 16 Mbit flash memory, for example, one is so configured that each one erase block is constituted of 64 Kbytes, and another is so configured that each one erase block is constituted of 8 Kbytes.
Ordinarily, the portable instrument
21
and the semiconductor disk
20
are interconnected through a special interface (for example, a disk interface), so that it is an ordinary practice that a data transfer between the portable instrument
21
and the semiconductor disk
20
is performed in units of sector, which is composed of 512 bytes.
Next, a data management in disk apparatuses will be described. An on-disk data structure in a hard disk or a floppy disk is different depending upon an operating system (OS) for supporting the disk apparatus, if it is compared in detail, but a fundamental data structure can be said to be the same. Here, the MS-DOS (Microsoft Disk Operating System) will be described as one example.
In the MS-DOS, as shown in
FIG. 4
, a storage area
50
on the disk is divided into four areas, namely, a reservation area
51
, a FAT (File Allocation Table) area
52
, a directory area
53
and a data area
54
. Incidentally, a minimum storage unit in the disk is a sector.
When a user uses the disk apparatus, it is unnecessary for the user to know where a file concerned is on the disk. This is all managed by the disk operating system. If a designated file name is given, the disk operating system can know a position within the data area
54
where the file concerned is stored, on the basis of the data in the directory area
53
and the FAT area
52
on the disk.
This method is illustrated in FIG.
5
. The directory area
53
stores file names
60
each corresponding to one file and FAT entry numbers
61
each indicating where the corresponding file exists on the disk. Actually, the directory area
53
stores other data including file attribute information, but since information other than the above two kinds of information has no close relation of the subject matter of the present invention, explanation thereof will be omitted.
When the disk operating system prepares the file, the disk operating system allocates the file into the data area
54
, not in units of sector, but in units of cluster which has the same size as that of the sector or a size corresponding to a pluralit
NEC Corporation
Peikari B. James
Young & Thompson
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