WO2007039674A1

WO2007039674A1 - Removable cartridge for storing digital data and removable cartridge reader

Info

Publication number: WO2007039674A1
Application number: PCT/FR2005/002426
Authority: WO
Inventors: Grégoire DECROIX
Original assignee: Decroix Gregoire
Priority date: 2005-10-03
Filing date: 2005-10-03
Publication date: 2007-04-12

Abstract

The invention relates to a removable cartridge (10) for storing digital data, which is intended to be inserted into a removable cartridge reader (12) and which comprises a plurality of storage devices (141, 142, ..., 14n) and an interface (16) for exchanging data between said storage devices and the reader. For each storage device (141, 142, ..., 14n), the interface comprises a specific communication channel (181, 182, ..., 18n) for said device, which can be accessed using one read/write controller (26) in order to read/write digital data on the cartridge.

Description

Removable digital data storage cartridge and removable cartridge drive.

The present invention relates to a removable digital data storage cartridge for insertion into a removable cartridge reader. It also relates to a removable cartridge reader.

The invention applies in particular to the secondary storage of data (backup and transmission of data).

More specifically, the invention relates to a removable digital data storage cartridge of the type comprising a plurality of storage devices and an interface for exchanging data between these storage devices and the cartridge reader.

For example, the RXT ™ solution marketed by the company is known.

Spectra Logic Corporation. This solution comprises a removable cartridge comprising several Winchester technology hard disks and a data exchange interface with a suitable reader, in which a read / write controller operating according to a predefined read / write mode manages, on the one hand, the exchanges with the storage devices inside the cartridge

RXT ™ and the exchanges between the RXT ™ cartridge and the adapted reader through a single communication channel.

The predefined read / write mode is for example one of the RAID modes

("Redundant Array of Independent Dises") known. RAID modes have been defined to provide different ways to read or write data to multiple storage devices, some of which allow for redundancy of stored information.

The RAID 0 mode allows the distribution of blocks of data to be stored in the cartridge between the storage devices it contains. In this read / write mode there is no redundancy but a possibility of simultaneous access to each hard disk of the cartridge. Thus, the storage capacity of the cartridge is the sum of the storage capacities of the storage devices it contains. In addition, potentially, the flow rate of the cartridge can reach the sum of the flow rates of each storage device.

RAID 1 mode provides redundancy by duplicating the blocks of data to be stored in the cartridge. Concretely, if the cartridge comprises two storage devices, each block of data to be memorized is written both in the first and in the second storage device. Thus, in case of failure of one of the storage devices, the other continues to operate and no data is lost. Thus, compared to a cartridge having a single storage device, performance is improved in reading since two readings in two different locations can be performed simultaneously, but slightly degraded in writing since the operation must be performed twice.

Other RAID levels, for example RAID 3 or RAID 5, involve a notion of parity. From a predetermined number of data blocks to be distributed in a plurality of hard disks, a computation is performed on the corresponding binary data to generate an additional block to be stored as well. This block, called a "parity block", allows the reconstruction of missing data in case of loss of one of the blocks of data. Thus, if one of the storage devices of the RXT ™ cartridge fails, the blocks it contained can be rebuilt. In particular, in RAID 3 mode, a hard disk is dedicated to storing parity blocks. In RAID 5 mode, the parity blocks are distributed like all other digital data blocks on all storage devices in the cartridge. RAID 3 and RAID 5 modes require at least three storage devices in the cartridge. In the state of the art mentioned above, from the point of view of the reader, the RAID mode

5 read / write is imposed by the RXT ™ cartridge. In addition, the plurality of storage devices of the RXT ™ cartridge is viewed as a global storage unit accessible via a single communication channel provided by the exchange interface between the RXT ™ cartridge and the corresponding reader. From the point of view of the RXT ™ cartridge, the RAID mode is imposed by construction by the read / write controller it contains.

These constraints pose problems in terms of flexibility and interoperability between the different secondary storage technologies. In particular, in the case of the RXT ™ cartridge, the interface further comprises a tape drive emulator, imposing a sequential and single-stream operation of the reader, which causes some of the advantages of the presence of hard disks to be lost. the cartridge that allow them direct multi-stream access.

In addition, more generally for the existing cartridges, it is necessary during the design of these cartridges to optimize them according to the following two criteria: - improve the storage capacity and access performance of the storage devices they contain; and

- improve the access mode to the different storage devices managed by the read / write controller. These two parameters to be optimized are not necessarily always compatible and simple to take into account together.

The invention aims to solve the aforementioned problems by providing a removable digital data storage cartridge with flexibility and interoperability qualities between different technologies. In addition, the invention aims to design removable cartridges for which the technological choices are not dictated by the optimization of incompatible parameters.

The subject of the invention is therefore a removable digital data storage cartridge of the aforementioned type, characterized in that the interface comprises, for each storage device, a communication channel specific to this storage device and accessible by the same reading controller. / write the reader, for reading / writing digital data in the cartridge.

Thus, a read / write controller no longer has to be integrated in the removable cartridge but in the reader. Since it is this controller that manages the access mode to the various storage devices of the cartridge, the access mode improvement parameter is no longer to be considered when designing the removable cartridge. In addition, flexibility of use and interoperability between different technologies are conferred by the presence of several communication channels accessible by the reader.

Each storage device of a removable cartridge according to the invention may be chosen from the set of elements consisting of a solid memory component, a hard disk, a flexible disk, an optical disk, and a magnetic tape.

Of course, the storage devices of the cartridge may be of the same nature or of different natures. The presence of an independent communication channel for each storage device in the cartridge interface makes it possible to imagine a large variety of possible cartridges while ensuring compatibility between these cartridges and the same type of reader.

In a preferred embodiment, a removable cartridge according to the invention comprises two 2.5 inch hard disk drives (this format corresponds to to a disc of 69.85 mm wide and 9.5 mm thick) each, as storage devices.

This number and size of hard disks used as storage devices for the cartridge, allow to design removable cartridges format corresponding to the standard formats known today.

Optionally, a removable cartridge according to the invention comprises a RAID mode selector, this RAID mode to be used by the read / write controller of the reader in which the cartridge is intended to be inserted to read / write data in the cartridge. Although it is the reader / writer controller of the drive that manages the RAID mode, it must be imposed by the removable cartridge, so that it is possible to read or write data using of different readers. Thus, thanks to the RAID mode selector, the drive in which the removable cartridge is inserted adapts its read / write controller according to the indicated RAID mode. Also optionally, a removable cartridge according to the invention further comprises a memory for storing data identifying and qualifying the cartridge, different from the storage devices, readable by a reading module of the reader in which the cartridge is intended to be inserted. This cartridge identification and qualification data, which is not strictly the digital data to be stored in this removable cartridge, allows a drive in which the cartridge is inserted to obtain a certain amount of information. useful on the cartridge before reading or writing data to it. The invention also relates to a removable digital data storage cartridge reader, for cartridges each comprising a plurality of storage devices, comprising an interface for exchanging data with the storage devices of a cartridge intended to be used. inserted in the reader, characterized in that it comprises a read / write controller, for reading / writing of the digital data in the cartridge, this controller comprising, via the interface, access means independent to several channels of communications of the cartridge, each communication channel to which it has access being associated with one of the storage devices of the cartridge.

In a preferred embodiment of the invention, the removable cartridge reader comprises: a dedicated port for connecting it to an external memory element including an encryption / decryption key, and

means for encrypting / decrypting the data to be written / read in the cartridge by means of this key. The dedicated port is for example a USB port.

Thus, using this external memory element, it is possible to encrypt digital data to be stored in the removable cartridge or to decrypt digital data stored in encrypted form in the removable cartridge, for security reasons. Thanks to the dedicated port and the means of encryption / decryption, it is the cartridge reader that performs this function. Any problem of reconfiguration of an encryption / decryption key during the replacement of a reader according to the invention by another in a computer system is thus solved in this way. Similarly, the propagation of the encryption / decryption key between several readers sharing the same set of cartridges can be done by generating as many external memory elements as readers, to ensure compatibility between them.

In another preferred embodiment of the invention, the removable cartridge reader comprises:

an opening for loading a cartridge to be inserted in the reader,

means for accessing the contents of the cartridge,

- Flap means of the cartridge to a loading position in which it cooperates with the means for accessing the contents of the cartridge, the flap means being movable between a rest position when no cartridge is inserted into the reader and one of a plurality of different service positions when the cartridge is in its loading position, each service position corresponding to a predetermined thickness of the cartridge.

It is thus possible to design a cartridge reader of standard format, which can read a plurality of cartridges of different thicknesses.

Optionally, a removable cartridge reader according to the invention may include an emulator for connecting the reader to at least one host system, the emulator including at least one tape drive emulation and a direct access disk emulation. to allow indifferently connection of the reader for management in sequential or direct access mode. The invention will be better understood with the aid of the description which follows, given solely by way of example and with reference to the appended drawings, in which:

- Figure 1 shows schematically the general structure of a digital data storage assembly comprising a removable cartridge and a reader according to the invention;

FIG. 2 is a perspective view of a removable cartridge according to the invention;

- Figure 3 is a rear view in perspective of a reader according to the invention;

FIG. 4 represents a plurality of removable cartridges according to the invention of different formats; and

FIG. 5 is a perspective view of a possible embodiment of the assembly of FIG. 1. The assembly represented in FIG. 1 comprises a removable digital data storage cartridge 10 intended to be inserted into a device. drive 12 removable cartridges.

The removable cartridge 10 comprises a plurality of storage devices 14 ,, 14 ₂₎ ... 14 _n and an interface 16 for exchanging data between these storage devices and the reader 12. Each storage device 14i, 14 ₂ , ... or 14 _n is for example a solid memory component, a hard disk, a floppy disk, an optical disk or a magnetic tape.

In a preferred embodiment of the invention, the removable cartridge comprises two storage devices 14i and 14 ₂ , each consisting of a 2.5-inch hard disk.

Indeed, the methods of direct and random access to information imply, for the time being, the use of hard disks or electronic memory components. If 3.5-inch hard disk drives (this size is a 101.6 mm wide disk) should be automatically eliminated for their fragility, smaller hard disk drives designed for mobile systems can to be privileged. Aside from size and impact resistance, 2.5-inch hard drives are also designed to save power, with repeated stop / start cycles. A cartridge based on such hard disks can provide a direct access method and transfer performance relating to the hard disks employed. Of course, smaller hard drives can be used, such as the 1 inch format, and their number can be increased, for example greater than or equal to 3. It is then possible to integrate into the cartridge the electronics necessary for manage data transmissions in RAID 5 mode for example. The data exchange interface 16 comprises a communication channel

18i specific to the storage device 14i, a communication channel 18 ₂ specific to the storage device 14 ₂ , and a channel 18 _n specific to the storage device 14 _n .

Thus, it is possible to independently access each of the storage devices 14- ,, 14 ₂ , ... or 14 _n of the removable cartridge 10, via the communication channel which is specific to it.

In addition, the removable cartridge 10 comprises a memory 20 for storing and identifying data of the cartridge, different from the storage devices 14i, 14 ₂ , ... 14 _n , readable via a communication channel 22 of the interface 16 of its own. Finally, the removable cartridge 10 includes a RAID mode selector 24 defining the RAID mode to be used by the reader 12 in which the cartridge is intended to be inserted to read / write data in the cartridge.

By providing the interface 16 of the cartridge 10 with a plurality of communication channels, it becomes possible to optimize the transfer rates between the cartridge and the reader and thus meet the current and future flow requirements.

In addition, the multiplicity of communication channels implies a possible separation of the storage devices of the cartridge, each using its own channel. RAID redundancy becomes possible by allowing the reader to manage the distribution of the writing. The reader 12 comprises a read / write controller 26 for reading / writing digital data in the cartridge 10. This controller 26 is designed to operate in one or more read / write modes, for example the RAID 0 and RAID modes. 1 to RAID 6.

To do this, the controller 26 is connected, via a communication channel 30, to an interface 28 for exchanging data with the storage devices 14-, 14 ₂ 14 _n of the cartridge 10. The The data exchange interface 28 allows the reader 12, and more precisely the controller 26, to access each of the communication channels 1S ₁ , 18 ₂ ,... 18 _π specific to each of the storage devices 14 ₁₇ 14 ₂ , ..., 14 _n of the cartridge 10. The controller 26 thus comprises, via the interface 28, independent access means to each of the communication channels 18i, 18 ₂ , .--, 18 _n of the interface 16 of the cartridge 10.

In addition, the reader 12 comprises a reading module 32 having access to the storage memory 20 for identification and qualification data of the cartridge 10, via the communication channel 22 of the interface 16 of the cartridge. 10.

The reader module 32 of the reader 12 is adapted to transmit the data that it can read from the identification and qualification data storage memory 20 to the controller 26 before the latter reads or writes data into the cartridge. 10.

The reader 12 furthermore comprises a device 34 for reading the RAID mode defined by the RAID mode selector 24 of the cartridge 10. The RAID mode selector 24 is designed to be able to switch between several possible RAID modes for the cartridge 10.

The reading device 34 is adapted to recognize the mode defined by the RAID mode selector 24 when the cartridge 10 is inserted in the reader 12.

The reader 12 also comprises a circuit 34 for encrypting / decrypting the data to be written / read in the cartridge 10. This encryption / decryption circuit is connected to the controller 26 to encrypt the data before transmission to the storage devices of the cartridge 10 , or decipher the data after their reception.

The reader 12 therefore has a dedicated port 38 for its connection to an external memory element 40, for example a USB key having a type B connector and containing an encryption / decryption key.

Thus, the data can be encoded before being stored in the removable cartridge 10, so that it can only be read by a reader sharing the same encryption / decryption key.

The encryption / decryption key is stored in the key 40 in the form of an encrypted file, obtained for example by means of the encryption / decryption key and the serial number of the key 40 combined.

According to the same principle, the reader calculates a static session key by combining the serial number of the removable cartridge with the encryption / decryption key. This session key can only work with the unique cartridge / key pair of encryption / decryption to the exclusion of any other possible pair.

This static session key is used to encrypt the data before writing or to read them after reading, in the corresponding cartridge, when it is inserted in the reader 12. When the cartridge is ejected, the static session key is erased. so that a new key can be recreated with the next cartridge. It will be recreated identically, if the same encryption / decryption key and the same cartridge share the same drive.

Conventionally, the reader 12 also comprises: - an emulator 42 for connecting the controller 26 to one or more systems interfaces 44- ,, 44 ₂ 44 _n which may be of different types;

an emulator 46 to an automation interface 48;

a maintenance interface 50. The emulator 42 advantageously comprises a tape drive emulation and a direct access disk emulation so as to allow the connection of the reader to a host system for management in sequential access mode or direct.

In a possible embodiment of the invention, the maintenance interface 50 is merged with the dedicated port 38. In this case, the dedicated port 38 is a USB port equipped with a type B connector.

FIG. 2 is a perspective view of the cartridge 10. In this view, it should be noted that the interface 16 of the cartridge comprises two communication channels 1S ₁ and 18 ₂ , each connected to a storage device, preferably a disk Hard 2.5 inch format. In addition, between these two communication channels Ie ₁ and 18 ₂ , there is the selector 24 RAID mode to be used by the controller 26 of the reader 12.

Figure 3 shows the reader 12 in perspective, seen from behind. In this perspective view, there is a system interface 44, the automation interface 48 and the USB port 38 dedicated to the connection of a USB key encryption / decryption, this dedicated port 38 being for example confused with the interface maintenance 50.

As shown in FIG. 4, the removable cartridge 10 can have several thicknesses, while being of standard width and depth. For example, for a width and depth of 4.15 inches (105.4 mm) it can be thick a = 1 inch (25.4 mm), of average thickness b = 0.85 inch (21.6 mm) or thin in thickness c = 0.5 inch (12.7 mm).

Indeed, to simplify its integration, the removable cartridge 10 according to the invention should preferably be compatible with existing formats. Thus, with the aforementioned dimensions, the manipulations are easy while leaving an interior space large enough to install a large number of components in the cartridge.

To maintain maximum flexibility and compatibility with existing products, the thickness of the cartridge 10 must be set within a tolerance range between a and c. For example, DLT and SDLT cartridges are 1 inch thick, SAIT cartridges and LTO cartridges are 0.85 inch thick. In addition, the needs of consumer electronics increasingly require the use of compact removable cartridges justifying thicknesses of 0.5 inches.

In any case, the loading operations of the removable cartridge 10 in the reader 12 involve precise mechanical positioning. To allow this precise positioning, reference surfaces must guarantee this positioning in the three axes of a Cartesian reference system. The removable cartridge 10 therefore has on one of its side walls a ramp 60 for positioning it precisely in the reader 12. This ramp 60 has a predetermined width L, begins at a predetermined height H from the base of the cartridge 10 and forms a predetermined angle θ with this base, regardless of the thickness of the cartridge.

In a conventional manner, the cartridge may further comprise gripping holes, for example in the format of Vi inch tape cartridges DLT, SDLT, SAIT or LTO.

In FIG. 5, there is shown in perspective a removable cartridge 10 of any thickness a, b or c, comprising a ramp 60 allowing its precise positioning in the reader 12. This, to force the positioning of the removable cartridge 10 in a loading situation in which it cooperates with means 62 for access to the contents of the cartridge, comprises a guide plate 64 on which the base of the cartridge 10 comes to rest and a leaf spring 66 pressing on the face upper removable cartridge 10 to fold on the tray 64.

The leaf spring is mounted on the housing of the reader 12, by one of its edges fixed above an opening of the housing through which the cartridge is inserted. removable. The opposite edge of the leaf spring 66, intended to be in contact with the removable cartridge 10, is optionally provided with a roller 68 sheathed with a synthetic rubber material.

In the rest position, when the removable cartridge 10 is not in the reader 12, the leaf spring 66 is in contact with the guide plate 64 via the roller 68. In the operating position, different according to the thickness a, b or c of the removable cartridge 10, the leaf spring 66 is in contact with the upper face of the removable cartridge 10 inserted in the reader 12, via the roller 68. To reduce the mechanical complexity of the reader 12, in order to limit the risk of failure and reduce production costs, the connection between the removable cartridge 10 and the reader 12 is limited to an electrical and logical connection. A simple electrical connection between the cartridge and the reader allows the use of known interface standards and minimizes development costs. A common interface emulation can be added to standardize cartridges and allow different technologies to work in the drive. Thanks to this principle, different cartridges can be replaced or coexist even if they host different storage technologies.

It will also be noted that limiting the mechanical interactions between the cartridge and the reader makes it possible to improve the reliability of the assembly. In addition, some criteria must be taken into account:

- allow the disconnection of the cartridge without power failure, hot;

- enable a throughput that corresponds to current and future performance;

- Provide a reduced number of cables to simplify connections;

- to ensure a reliability of the connectors which guarantees a large number of connection / disconnection cycles; and

- choose inexpensive and well-known technology to reduce development and production costs.

From these criteria, the choice naturally goes to an SAT A2 type interface. Its point-to-point topology integrates the concept of hot-pluggable and also allows a bit rate of 300 megabytes per second. In addition, the system only requires four wires to establish a communication channel. A preferred format choice for the 12 drive is that of 5.25 inches (this format corresponds to a drive width equal to 146.5 mm) in half height. An adapter to the full height format can be mounted in computer systems that use this full height format. The mechanism for inserting the cartridge 10 into the reader 12 will now be detailed, again with reference to FIG.

Thus, in a first step 100, a user inserts the removable cartridge 10 in the reader 12 by its opening.

In the next step 102, while the removable cartridge is partially inserted in the reader 12, the leaf spring 66 is deformed upwards to adapt to the thickness of the removable cartridge 10 and forces the positioning of the on the guide plate 64.

Then, during a step 104, when the removable cartridge 10 is sufficiently inserted into the reader 12, the guide plate 64 accompanies the removable cartridge 10 to its loading position. If the connection interface of the cartridge is protected by a flap, it opens.

Finally, in a last step 106, the connectors of the cartridge and the reader establish an electrical contact and the cartridge is locked in the electrical connection position to the reader 12. It is clear that a removable cartridge as described above allows a simple and efficient access to the storage devices it contains, comprising for each storage device a communication channel directly accessible by a read / write controller disposed in a corresponding reader. It also clearly appears that a removable cartridge reader as described above allows the easy reading / writing of data in the removable cartridge, with the further possibility of encrypting / decrypting this data, without requiring calculation capabilities of the host system in which it is integrated, since it itself comprises the means of encryption / decryption. The use of a key (for example a USB key) comprising the encryption / decryption key used by the reader and connectable directly to the reader by a dedicated port makes this operation more secure.

Finally, it is clear that a removable cartridge reader as described above allows to receive cartridges of different thicknesses while having a standard opening for the reception of these cartridges, thanks to spring leaf positioned to exert pressure on the cartridge to be inserted, so as to position it inside the reader in a predetermined loading situation.

Note however that the invention is not limited to the embodiment described above.

For example, any type of storage device can be integrated in a removable cartridge according to the invention, from the moment when it is associated with a standard communication channel vis-à-vis the reader 12.

For example, the use of electronic memory components can be envisaged to provide random access means. In addition to access time performance, the throughput of these technologies and their impact resistance can be made particularly advantageous for certain applications and environments, such as heavy industry, aviation, defense or industry. automotive, naval and space. The type of memory technology to use does not suffer from any restriction other than economic. The battery-backed RAMs, flash-type persistent memories or reprogrammable EEPROM memories are all of technological interest. In addition, by their size and the space available in the cartridge, a shield system can be added to protect them from electromagnetic radiation so as to make them even more suitable for these uses.

Similarly, the read / write modes defined between the removable cartridge and the drive may be other than the RAID modes mentioned.

In addition, although it is preferred that a removable cartridge according to the invention comprises two 2.5 inch hard disks each, it is possible to design cartridges having a larger number of smaller format hard disks.

Finally, there has been described a reader comprising a housing and a loading opening, but the reader could be reduced to a programmable component of the ASIC type (of the English "Application Specifies Integrated Circuit") coupled to connectors (of which at least one connector for each communication channel).

Claims

A removable digital data storage cartridge (10) for insertion into a removable cartridge drive (12) having a plurality of storage devices (14 |, 14 ₂ 14 _n ) and an interface (16) for exchange of data between these storage devices and the reader, characterized in that the interface comprises for each storage device (14-ι, 14 ₂ , ..., 14 _π ) a communication channel (18-ι, 18 ₂ , ..., 18 _n ) specific to this storage device and accessible by the same controller (26) reading / writing of the reader, for reading / writing of the digital data in the cartridge.

2. removable cartridge (10) according to claim 1, wherein each storage device (14 _{1 (} 14 ₂ , .... 14 _π ) is selected from the set of elements consisting of a solid memory component, a hard disk, a floppy disk, an optical disk, and a magnetic tape.

3. Removable cartridge (10) according to claim 1, comprising two 2.5 inch hard disks each, as storage devices (14i, 14 ₂ , ..., 14 _n ).

4. A removable cartridge (10) according to any one of claims 1 to 3, comprising a RAID mode selector (24), this RAID mode to be used by the controller (26) reading / writing of the reader (12) in which cartridge is to be inserted to read / write data into the cartridge.

5. Removable cartridge (10) according to any one of claims 1 to 4, further comprising a memory (20) for storing data identifying and qualifying the cartridge, different from the storage devices, (14i, 14 ₂ , ..., 14 _n ) readable by a read module (34) of the reader (12) in which the cartridge is to be inserted.

6. Reader (12) of removable digital data storage cartridges, for cartridges each having a plurality of storage devices, having an interface (28) for exchanging data with the storage devices (14-ι, 14 ₂ , ..., 14 _π ) of a cartridge (10) intended to be inserted into the reader, characterized in that it comprises a read / write controller (26), for reading / writing digital data in the cartridge, this controller comprising, via the interface (28), means of access independent to several communication channels (18i, 18 ₂ , ..., 18 _n ) of the cartridge, each channel of communication to which it has access being associated with one of the storage devices of the cartridge.

7. A removable cartridge reader (12) according to claim 6, comprising: a dedicated port (38) for its connection to an external memory element (40) having an encryption / decryption key, and

means (36) for encrypting / decrypting the data to be written / read in the cartridge (10) by means of this key.

The removable cartridge drive (12) of claim 7, wherein the dedicated port (38) is a USB port.

9. Reader (12) of removable cartridges according to any one of claims 6 to 8, comprising:

an opening for loading a cartridge (10) to be inserted in the reader; means (62) for accessing the contents of the cartridge;

- means (66, 68) for flipping the cartridge to a loading position in which it cooperates with the means for accessing the contents of the cartridge, the flap means being movable between a rest position when no cartridge n ' is inserted in the reader and one of several different service positions when the cartridge is in its loading position, each service position corresponding to a predetermined thickness (a, b, c) of the cartridge.

The removable cartridge reader (12) according to any one of claims 6 to 9, comprising an emulator (42) for connecting the reader (12) to at least one host system, the emulator (42) having at least one Tape drive emulation and direct-access disk emulation so that the drive connection can be interchanged for sequential or direct access mode management.