0’
`
`Europaisches Patentamt
`European Patent Office
`Office européen des brevets
`
`® Publication number: 0
`
`@
`
`EUROPEAN PATENT APPLICATION
`
`@ Application number: 913079132
`
`@ Int. C|.5: G06F 3/06, G11B 7/013
`
`@ Date of filing : 29.08.91
`
`Priority: 31.08.90 JP 230807l90
`08.07.91 JP 193435l91
`12.07.91 JP 198414I91
`12.07.91 JP 198415I91
`
`Date of publication of application :
`18.03.92 Bulletin 92/12
`
`Designated Contracting States:
`DE FR GB IT NL
`
`® Applicant: KAWASAKI STEEL CORPORATION
`1-28, 1-chome, Kitahonmachidori
`Chuo-ku Kobe-shi Hyogo-651 (JP)
`
`@ Inventor: Sawada, Kaname, Tokyo Head
`Office
`Kawasaki Steel Corp., 2-3, Uchisaiwai-cho
`2-chome
`Chiyoda-ku, Tokyo 100 (JP)
`Inventor: Takahashi, Yoshitaka, Tokyo Head
`Office
`Kawasaki Steel Corp., 2-3, Uchisaiwai-cho
`2-chome
`Chiyoda-ku, Tokyo 100 (JP)
`Inventor: Kanagawa, Masaaki, Tokyo Head
`Office
`Kawasaki Steel Corp., 2-3, Uchisaiwai-cho
`2-chome
`Chiyoda-ku, Tokyo 100 (JP)
`
`Representative : Stebbing, Timothy Charles et
`al
`Haseltine Lake & Co. Hazlitt House 28
`Southampton Buildings Chancery Lane
`London WC2A 1AT (GB)
`
`Hard disk emulator.
`
`@ A hard disk emulator (2) useful as a computer
`auxiliary memory device,
`comprising a hard
`disk drive (4) or non-volatile memory used as a
`cache memory together with an optical disk
`drive (5) as a main memory and an emulation
`unit (3) located among a host computer (1), the
`optical disk drive (5), and the hard disk drive (4)
`or non-volatile memory and operable in
`res-
`ponse to requests for writing and reading of
`data by the host computer (1) utilizing the hard
`disk drive (4) or non-volatile memory as the
`cache memory, whereby use
`of dedicated
`hardware and software can be eliminated upon
`incorporation of the optical disk drive (5) and
`low throughput of the optical disk drive (5) can
`be compensated.
`
`EP0475639A2
`
`Jouve, 18, rue Saint-Denis, 75001 PARIS
`
`Apple 1036
`U.S. Pat. 9,189,437
`
`

`
`EP 0 475 639 A2
`
`invention relates to a hard disk
`The present
`emulator such as an optical disk drive, etc., as one of
`auxiliary memory devices in computers.
`Optical disk drives enjoy many advantages, com-
`pared with a hard disk drive widely used as auxiliay
`memory devices in computers, that i) disks in use are
`exchangeable, ii) there is no fear of any crush occur-
`ring because of its non-contact recording system, iii)
`life time of data on disks is so long, and iv) they have
`large memory capacity, and so on.
`The optical disk drive has been noticed as an
`auxiliary memory device instead of the hard disk drive
`in recent years.
`However, in order to permit the optical disk drive
`to widely spread as an auxiliary device in a computer,
`it has the following problems to be solved at the pre-
`sent time.
`
`First, since the hard disk drive has wide appli-
`cations as an auxiliary memory device in a computer,
`it is needed, for connecting the optical diskdrive to the
`computer, to have new hardware and software.
`lower
`Second,
`the optical disk drive has
`throughput than that of the hard disk drive. For factors
`of the optical disk drive having the lower throughput,
`it can be considered that first, seeking takes a long
`time, second a data error rate before error correction
`
`is severe and hence verification after writing is indis-
`pensable, and third the probability of occurrence of
`defect block replacement is high in view of the error
`rate problem.
`Third, in the case where the optical disk drive is
`of a M0 type overwriting is unlike and reversing time
`of magnetization direction is required between an
`erasing cycle and a writing cycle.
`The optical disk drive thus suffers particularly in
`writing from a problem that its processing speed is
`severely lowered compared with the case in the hard
`disk drive.
`
`The optical disk drive thus has many advantages
`but oppositely has many disadvantages
`simul-
`taneously.
`In view of the drawbacks with the prior art, it is a
`first object of the present invention to eliminate the
`need of dedicated hardware and dedicated software
`
`upon incorporation of the optical disk drive and com-
`pensate the low throughput of the optical disk drive.
`To achieve the above first object, the present
`invention comprises an optical disk drive as a main
`memory, a hard disk drive or a non-volatile memory
`used as a cache memory together with the optical disk
`drive, and an emulation unit located among a host
`computer, said optical disk drive, and the hard disk
`drive or non-volatile memory, the emulation unit being
`operable in response to requests of writing and read-
`ing of data sent from the host computer using said
`hard disk drive or non-volatile memory as the cache
`memory.
`More specifically, with the provision of interface
`
`specifications conforming to arbitrary hard disk drive
`specifications, need of new software and hardware is
`eliminated upon incorporation of the optical disk drive,
`and the optical disk drive is recognized as a hard disk
`drive by by the connected host computer and assures
`emulation as a large capacity hard disk drive by
`exchanging its optical disk.
`the
`invention reduces
`Further,
`the present
`aforementioned problems with the optical disk drive
`by making use of a hard disk drive or non-volatile
`memory as a cache memory upon such emulation.
`Hereinafter, a hard disk drive or non-volatile
`memory used as such a cache memory is also refer-
`red to as a data cache unit.
`In the case where data to be written sent from the
`
`host computer is recorded in said hard disk drive or
`non-volatile memory while said host computer reads
`data already recorded, read data is read out from said
`hard disk drive or non-volatile memory and said opti-
`cal disk drive. If there is no access from said host com-
`
`puter, said recorded data is transferred from said hard
`disk drive or non-volatile memory to said optical disk
`drive or a predetermined amount of data adjoining a
`read data area is transferred from the optical disk
`drive to the hard disk drive or non-volatile memory.
`With the provision of an emulation function of the
`hard disk drive as described above, need of dedicated
`hardware and dedicated software is eliminated upon
`incorporation of the optical disk drive, and with the
`provision of the so-called cache memory and back-
`ground processing low throughput of the optical disk
`drive is compensated.
`In accordance with the present invention, as des-
`cribed above, there are utilized intactly the advan-
`tages of the optical disk drive such as exchangeability
`of disk, a long life and large capacity, and crush free,
`and in addition there can be compensated the disad-
`vantage of
`the optical disk drive having low
`throughput by providing a cache memory and the
`background processing. Further, when highly ran-
`domly accessing data is recorded, the throughput of
`the optical disk drive can also be expected to exceed
`that of an emulation target hard disk drive.
`Further, in accordance with the present invention,
`with the provision of emulation function of the hard
`disk drive, there is eliminated the use of hardware and
`software inherent to the optical disk drive, and the
`optical disk drive is also connectable with a host com-
`puter instead of the hard disk drive.
`However,
`if the host computer frequently takes
`accesses, there might be prodeced a fear that a pro-
`cessing can not catch up with those accesses, of
`updating data in the optical disk drive as the main
`memory following the newest data of cache data
`recorded in the hard disk drive or non-volatile memory
`used as the cache memory.
`If it is so, there might be produced a first problem
`that the hard disk drive or non-volatile memory is filled
`
`

`
`EP 0 475 639 A2
`
`up whith the cache data not transferred to the main
`memory and remaininig recorded in the hard disk
`drive or non-volatile memory.
`The data recorded in the hard disk drive or non-
`
`volatile memory used as the cache memory carries
`information at which address of the optical disk drive
`each data is originally to be recorded. Hereinafter,
`such information will be referred simply to as address
`information.
`
`If there is produced the above situation where the
`host computer frequently takes accesses, there might
`be produced a second problem that such address
`information is accumulated and memory capacity of a
`work memory in which such a address information is
`stored expires.
`Once the hard disk drive or non-volatile memory
`used as the cache memory is thus filled up with the
`cache data or the work memory for recording the
`address information therein is filled up with the
`address infonnation at the worst, a processing pro-
`ceeds of transferring the cache data in the hard disk
`drive or non-volatile memory to the optical disk drive
`and simultaneously a processing proceeds of putting
`in order the address information executed following
`the just-mentioned processing, whereby the acces-
`ses from the host computer must wait until the filled
`state disappears.
`Further, if such a filled state is reached and there-
`upon there occurs any access from the host computer
`at the worst, access time from the host computer is
`prolonged including the time the filled state disap-
`pears and results in the lowering of the function as the
`hard disks emulator.
`
`A second object of the present invention is to pre-
`vent, even under the conditions where the host com-
`puter frequently takes accesses, the function as the
`hard disk emulator from lowering to a fact that the hard
`disk drive or non-volatile memory used as the cache
`memory is filled up with the cache data which has not
`yet been transferred to a main memory and remains
`recorded in the hard disk drive or non-volatile memory
`or owing to a fact that the work memory is filled up with
`the address information.
`
`To achieve the second object, the present inven-
`tion is adapted such that said hard disk drive or non-
`volatile memory includes a fixed cache area for
`temporarily recording therein data at successive emu-
`lation addresses including emulation addresses fre-
`quently accessed, and a normal cache area for
`temporarily properly recording therein data other than
`said data at cache addresses where no data has been
`written.
`
`for
`invention provides,
`the present
`Further,
`achieving the second object, a method of allocating
`the successive emulation addresses including the
`emulation addresses of the data temporarily recorded
`in said fixed cache area in said hard disk emulator
`
`wherein fixedly defined predetermined successive
`
`emulation addresses are allocated as said succes-
`
`sive emulation addresses of the data temporarily
`recorded in said fixed cache area.
`
`Still further, the present invention provides, for
`achieving the second object, a method of allocating
`the successive emulation addresses including the
`emulation addresses of the data temporarily recorded
`in said fixed cache area in said hard disk emulator
`
`frequency for each emulation
`wherein access
`address of data accessed by said host computer is
`estimated and successive emulation addresses
`
`including at least emulation addresses of high access
`frequency are allocated as the successive emulation
`addresses of the data temporarily recorded in said
`fixed cache area.
`
`Yet still further, the present invention provides, for
`achieving the second object, a method of allocating
`the successive emulation addresses including the
`emulation addresses of the data temporarily recorded
`in said fixed cache area in said hard disk emulator
`
`wherein memory capacity of the fixed cache area of
`said hard disk drive or non-volatile memory used as
`a cache area upon the emulation is made greaterthan
`that of an area of said optical disk drive in which data
`is actually recorded and all emulation addresses cor-
`responding to the area of said optical disk drive in
`which data is actually recorded are allocated as the
`successive emulation addresses of the data tempor-
`arily recorded in said fixed cache area.
`As describeb previously, if there is brought about
`the situation where the host computer frequently
`takes accesses, the memory capacity of the hard disk
`drive or non-volatile memory (data cache unit) used
`as the cache memory is filled up or the work memory
`for recording therein the address information is filled
`up to lower the function as the hard disk emulator.
`For solving such relatively exceptional condi-
`tions, the present invention constructs the cache area
`in the data cache unit, i.e., the hard disk drive or non-
`volatile memory with two types of cache area: a nor-
`mal cache area and a fixed cache area.
`
`With the normal cache area, data accessed by
`the host computer is properly temporarily recorded at
`addresses in the hard disk drive where no data has
`been written.
`
`Accordingly, for utilizing such a normal cache
`area, it is necessary to previously record the address
`information in the work memory and the like.
`The hard disk emulator in the present invention is
`operable conformably to interface specifications in
`conformity with the specifications of an arbitrary hard
`disk drive.
`
`More specifically, any access by the host com-
`puter for recording into and reading from the hard disk
`emulator conforms to the specifications of a hard disk
`drive to be emulated.
`
`Upon the accessing by the host computer,
`addressing of accessed data to the hard disk emulator
`
`

`
`EP 0 475 639 A2
`
`also conforms to the specifications of a hard disk drive
`to be emulated.
`
`Hereinafter, such an address addressed by the
`host computer is referred to as an emulation address.
`For such emulation addresses, there are con-
`sidered ones addressed taking a predetermined byte
`number block as a unit irrespective of track numbers,
`cylinder numbers, and sector numbers, etc., i.e., one
`addressed following the serial numbers of all blocks
`of predetermined byte numbers, and ones addressed
`supposing a general hard disk drive and combining
`varieties of address values such as track numbers,
`cylinder numbers, and sector numbers, etc., and other
`ones similarly addressed. Those emulation addres-
`ses conform to the specifications of hard disk drive to
`be emulated and are not limited by the present inven-
`tion.
`
`Also, the optical disk drive as a main memory has
`a predetermined addressing format even though
`physical formats of information recording media are
`with spiral ones or with a plurality of concentric tracks.
`Hereinafter, any address addressed upon acces-
`sing data in the optical disk drive is referred to as an
`optical disk address.
`Emulation addresses and optical disk addresses
`are defined in one to one correspondence and so
`addresses of the optical disk drive are also assumed
`to be the emulation addresses for brevity.
`Further, the hard disk drive or non-volatile mem-
`ory as the data cache unit, also has a predetermined
`format of addressing for accessing data therein.
`Hereinafter, any address addressed upon acces-
`sing data in such a data cache unit is referred to as a
`cache address.
`In data transfer between the normal cache area
`
`in the data cache unit and the host computer and data
`transfer between the normal cache area and the opti-
`cal disk drive, correspondence between the cache
`addresses and the emulation addresses is provided in
`accordance with address information having been
`recorded in the work memory and the like.
`Such address information used upon accessing
`the data cache unit forms a correspondence table be-
`tween the cache addresses and the emulation
`
`addresses, i.e., a cache address table.
`On the other hand, the fixed cache area, one of
`the features of the present invention, provided in the
`data cache unit together with the normal cache area
`is one fortemporarily recording data at the successive
`emulation addresses including the emulation addres-
`ses frequently accessed.
`Further, the cache addresses in the fixed cache
`area and the successive emulation addresses allo-
`cated thereto are defined under one to one corres-
`
`pondence.
`Accessing such a fixed cache area does not
`require the address information required upon acces-
`sing the foregoing nom1a| cache area.
`
`Further, even though the host computer fre-
`quently records data at emulation addresses allo-
`cated to the fixed cache area, data recording to
`corresponding cache addresses in the fixed cache
`area is done simply by a predetermined number of
`times.
`
`if such a fixed cache area is
`More specifically,
`available, there can be avoided a fear that data is not
`yet transferred to a main memory and hence the
`cache area is filled up with data remaining recorded
`therein when the normal cache area is employed, or
`a fear that the work area is filled up with the address
`information owing to the use of the normal cache area.
`The present invention can thus solve, with the
`provision of the fixed cache area, the fear that a data
`cache unit is filled up with data as a result of the data
`being not transferred to the main memory or the fear
`that the work memory is filled up with address infor-
`mation to result in lowering of the function as the hard
`disk emulator, even when the host computertakes fre-
`quent accesses.
`Herein,
`it should be noticed that the present
`invention does not limit the memory capacity of the
`fixed cache area, and the ratio of the memory capacity
`of the fixed cache area to that of the optical disk drive
`as a main memory, and the method of allocating the
`successive emulation addresses to the fixed cache
`
`area, i.e., the fixed cache area allocating method in
`the hard disk emulator.
`
`In what follows, the method of allocating the fixed
`cache area in the hard disk emulator usable in the pre-
`sent invention will be exemplarily described.
`Fig. 5 is a diagram including a memory map indi-
`cative of first and second examples of the fixed cache
`area allocating method of the present invention.
`In the figure, a symbol A5 denotes the whole
`memory capacity area of the optical disk drive as a
`main memory. A symbol A4 denotes the whole cache
`area of the data cache unit as the hard disk drive or
`
`non-volatile memory.
`The whole cache area A4 of the data cache unit
`is divided to a fixed cache area A10a and a normal
`cache area A12a. The fixed cache area A10a is an
`
`area for temporarily recording data of successive
`emulation addresses including emulation addresses
`frequently accessed. The normal cache area A12A is
`an area for properly temporarily recording data other
`than an address region recorded in the fixed cache
`area A10a in the normal cache area A12a at cache
`addresses of the same where no data has been writ-
`ten.
`
`On the other hand, the whole memory capacity
`area 5A of the optical disk drive is divided to a fixed
`cache area allocation area A10b and a normal cache
`area allocation area A12b. The fixed cache area allo-
`cation area A10b is an area allocated to the fixed
`cache area A10a such that the fixed cache area A10a
`
`is employed upon caching data. Memory capacity of
`
`

`
`EP 0 475 639 A2
`
`the fixed cache area allocation area A10b is defined
`to be the same as that of the fixed cache area A10a.
`Individual addresses of the fixed cache area allo-
`cation area A10b and those of the fixed cache area
`
`A1 0a are in one to one correspondence, and hence
`correspondence between addresses of the one area
`and corresponding addresses of the other area can
`uniquely and promptly be estimated.
`The normal cache area allocation area A12b is an
`area allocated to the normal cache area A12a such
`
`that the normal cache area A12a is usable upon cach-
`ing data. Memory capacity of the normal cache area
`A12a used for caching data in the area A12b is less
`than that of the normal cache area allocation area
`
`A12b. This is because there is properly employed,
`upon caching data, cache addresses of the normal
`cache area A12a where no data has been written, and
`
`this shows the memory capacity of the data cache
`device can effectively be utilized.
`Herein, in thefirst example of the fixed cache area
`allocating method of the present invention the fixed
`cache area allocation area 10b allocated to the fixed
`
`cache area A10a provides fixedly defined predeter-
`mined successive emulation addresses, as illustrated
`in Fig. 5.
`Data in the fixed cache area allocation area A10b
`
`in the first example of the fixed cache area allocating
`method of the present invention is data in an area
`including successive emulation addresses corre-
`sponding to successive emulation addresses includ-
`ing emulation addresses of data accessed frequently,
`such for example as OS (operating system) manage-
`ment information and the like, whatever a running
`application program is.
`Further, OS management information associated
`with file management on the optical disk drive in the
`foregoing OS management information is usually to
`be recorded in the optical disk drive whole memory
`capacity area A5, and information concerning such
`file management is data frequently accessed what-
`ever a running application program, and so it is effec-
`tive to allocate the fixed cache area A10a so as to
`include such data.
`
`Further, in the second example of the fixed cache
`area allocating method of the present invention, the
`fixed cache area allocation area A10b is not fixedly
`allocated in the optical disk drive whole memory
`capacity area A5 as illustrated in Fig. 5. More specifi-
`cally, the fixed cache area allocation area A1 Ob in the
`second example of the fixed cache area allocating
`method is such that access frequency for each emu-
`lation address of data accessed by the host computer
`is estimated and successive emulation addresses
`
`including at least high access frequency emulation
`addresses are allocated to the fixed cache area A1 0a.
`
`The second example of the fixed cache area
`allocating method is useful in a case where access
`frequencies of data accessed by the host computer
`
`with a running application program are greatly diffe-
`rent among the emulation addressed, and so on, for
`example.
`In the case where access frequencies are greatly
`different among the emulation addresses as des-
`cribed above, the throughput of the hard disk emulator
`can be improved by allocating successive emulation
`addresses including high access frequency emulation
`addresses to the fixed cache area allocation area
`A10b.
`
`Fig. 6 is a memory map illustrating a third
`example of the fixed cache area allocating method of
`the present invention. In Fig. 6, symbols A4, A5, A10a
`and A10b are identical to those illustrated in Fig. 5. In
`Fig. 6, memory capacity of the data cache unit whole
`cache area A4 is the same as that of the whole mem-
`
`ory capacity area of the optical disk drive as the main
`memory. Further, the whole of the data cache unit
`while cache area A4 is the fixed cache area A10a.
`
`Accordingly, the whole of the optical disk drive whole
`memory capacity area A5 is also the fixed cache area
`allocation area A10b.
`
`In accordance with the third example of the fixed
`cache area allocating method, data in the data cache
`unit can thus be accessed without using any address
`information and the like, whatever emulation addres-
`
`ses of data accessed by the host computer are.
`Further, there is eliminated a problem that data which
`are not yet transferred to the optical disk drive as the
`main memory and remain recorded in the data cache
`unit are increased with which data the data cache unit
`
`is finally filled up, even though accesses by the host
`computer are frequent, and whatever emulation
`addresses of the data accessed at that time are. In the
`
`is unnecessary to
`it
`furthermore,
`third example,
`record the address information in the work memory
`and the like, and hence no problem is existent that
`such a work memory is filled up with the address infor-
`mation under the situation that accesses are fre-
`
`quently produced from the host computer.
`for
`The present
`invention is further adapted,
`achieving the foregoing second object, such that
`interface specifications conforming to predetermined
`hard disk drive specification are emulated using an
`optical disk drive as a main memory and a hard disk
`drive or non-volatile memory having a cache area for
`temporarily recording data accessed by a host com-
`puter properly utilizing cache addresses where no
`data has been written, and a plurality of pieces of
`address information which are to be written in a cache
`
`address table upon said emulation or which have
`been written in the same are compared with each
`other to determine whether or not respective cache
`data corresponding to the respective pieces of the
`address information can be integrated with each other
`in their state where they have been written in said
`cache area, and further if they are determined to be
`integrable at least a plurality of corresponding pieces
`
`

`
`EP 0 475 639 A2
`
`10
`
`address information integrating processing of the pre-
`sent invention will be described.
`
`Fig. 7 is a diagram illustrating a concatenation
`processing of the address information, an example of
`the address information integrating processing of the
`present invention.
`In Fig. 7, there are indicated in
`order from the left column, numbers (No.) for expla-
`nation, conditions by which associated items are pro-
`cessed, and details of
`the processings of
`the
`associated items.
`
`The concatenation processing of the address
`information illustrated in Fig. 7 is to concatenate dif-
`ferent pieces of address information in the case where
`adjacent cache data corresponding to those pieces of
`the address information are continuous in the state
`
`where they have been written in a cache area of the
`data cache unit as the hard disk drive or non-volatile
`
`memory.
`1 of the Fig. 7, a plurality of pieces of
`In No.
`address information corresponding to adjacent cache
`data in a cache area are united to one piece of the
`address information in the case where the adjacent
`cache data in the cache area are decided to be simply
`continuous in the state where the adjacent cache data
`have been written in the cache area based upon
`address information of a cache address table recor-
`
`ded in the work memory.
`the
`More
`specifically, cache addresses of
`address information corresponding to the adjacent
`cache data in the cache area are continuous because
`
`of the cache data being adjacent in the cache area.
`Accordingly, provided such cache data adjacent in the
`cache area are continuous also with respect to the
`emulation addresses, the pieces of the address infor-
`mation of those cache data can be united to one piece
`of the address information.
`
`In No. 2 of Fig. 7, provided the emulation addres-
`ses are decided to be continuous, partly overlapped
`upon writing cache data in the cache area anew and
`in the case where cache data getting to be adjacent
`in the cache area by writing, the emulation addresses
`get to be simply continuous in the case where they
`have been written likewise No. 1 by writing the cache
`data so as to overwrite an overlapped portion of the
`cache data.
`
`of the address information are integrated.
`Said determination on whether or not respective
`cache data can be integrated, can be determined from
`whether or not the pieces of the address information
`are continuous in their state where they have been
`written in said cache area, and if they are determined
`to have been continuous, then at least a plurality of
`corresponding pieces of the address information are
`concatenated to achieve the second object.
`Or said determination on whether or not respec-
`tive cache data can be integrated, can be determined
`from whether or not address information in certain
`cache data includes address information of cache
`
`data recorded therebefore, and if it is detennined to
`include the prior recorded address information, then
`the certain cache data is made valid to include the
`
`prior recorded address information to achieve the sec-
`ond object.
`More specifically, the present invention puts in
`order address information recorded in the work mem-
`
`ory for dealing with also relatively exceptional condi-
`tions that there frequently occur accesses of a request
`from the host computer of recording data and of a
`request from the same of regenerating data.
`Further, in accordance with the present invention,
`upon the address information recorded in the work
`memory being put in order, it is possible according to
`circumstances to reduce data in the cache area of the
`data cache unit.
`
`Thus, in accordance with the present invention,
`the problem can be prevented that the work memory
`is filled up with the address information therein, even
`under the conditions where there are frequently pro-
`duced accesses from the host computer. Further,
`it
`can also be prevented according to circumstances
`that recording capacity of the data cache unit is filled
`up.
`
`In what follows, an address integrating method in
`the hard disk emulater according to the present inven-
`tion will be described. The judgement of the present
`invention on whether or not cache data corresponding
`to a plurality of pieces of address information can be
`integrated with each other even under their state
`where they have been written in the cache area is
`achieved by comparing those pieces of the address
`information.
`
`Herein, the present invention does not limit con-
`crete conditions of the judgement on whether or not
`such a plurality of pieces of address information can
`be integrated by comparing those pieces of the
`address information with each other or concrete pro-
`cessing details corresponding to said judgement.
`Hereinafter, such judgement of the present inven-
`tion on whether or not pieces of the address infor-
`mation can be integrated and a predetermined
`processing following thejudgement are referred to an
`address information integrating processing.
`In the following, a concrete example of the
`
`Hereby, also in No. 2 of Fig. 7, the pieces of the
`address information of the adjacent cache data can
`be united to one piece of the address information
`likewise No. 1.
`Previous
`
`address
`
`information
`
`is
`
`therefore
`
`updated after writing of present cache data is termi-
`nated such that the present address information is
`included in the previous address information.
`In accordance with the concatenation processing
`in No. 2 in Fig. 7, capacity of the cache data recorded
`in the cache area can be reduced. Namely, a fraction
`of capacity of an overlapped portion of the previous
`cache data with the present cache data can be
`
`

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`11
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`EP 0 475 639 A2
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`12
`
`the total number of the address
`reduced. Further,
`information in the work memory can also be reduced.
`Fig. 8 is a diagram illustrating inclusing proces-
`sing of address information, an example of the integ-
`rating processing of address infonnation. Also in Fig.
`8, there are indicated likewise Fig. 7, in order from the
`left, numbers Nos. for explanation, conditions by
`which associated items are processed, and details of
`the processings of the associated items.
`In No. 1 in Fig. 8, the conditions are whetheror not
`address information having been recorded in the work
`memory corresponding to cache data having been
`recorded in the cache area of a data cache unit as the
`
`hard disk drive or non-volatile memory involves
`address information of the other cache data recorded
`before said cache data was recorded.
`Provided emulation addresses of address infor-
`mation of certain cache data involve emulation
`addresses of cache data recorded before the former
`
`cache data is recorded, associated emulation addres-
`ses of the optical disk drive as a main memory can be
`updated to the newest data only with the involving
`(newer) cache data. Accordingly, when the No. 1 con-
`ditions hold, the involving (newer) cache data is made
`valid. Further, when the No. 1 conditions hold, the
`involved (older) cache data is unnecessary and so the
`address information corresponding to the unneces-
`sary cache data is also unnecessary. The unneces-
`sary address information is thus abandoned and a
`plurality of pieces of the address information are
`united to one piece of the same.
`It should be noted that, upon any data being
`recorded in a disk as a recording medium of the opti-
`cal disk drive, writing of the data in the disk as the
`recording medium at a predetermined address of the
`same may sometimes be impossible owing to any
`trouble concern the disk as the recording medium. In
`such a case exchange processing is usually effected
`in the optical disk drive, but there may be caused
`problem that an exchange region is filled up although
`rarely or the optical disk drive suffers from any error
`in itself, in which case the writing in a disk of the optical
`disk drive at a predetermined address fails to nor-
`marily terminate.
`In the optical disk drive which does not cache
`data, even if such recording failure occurs upon
`recording therein data from the host computer, the
`optical disk drive can relatively easily deal with such
`failure. For example, once any recording failure
`occurs and errortermination information is transferred
`
`to the host computer, data not recorded could be
`recorded by appointing another address in a disk as
`a recording medium.
`However, provided there occur a