WO1993001595A1

WO1993001595A1 - Stack loader arrangement for an automated library system

Info

Publication number: WO1993001595A1
Application number: PCT/US1992/005484
Authority: WO
Inventors: Michael Edward Moy; Timothy Craig Ostwald
Original assignee: Storage Technology Corporation
Priority date: 1991-07-01
Filing date: 1992-06-30
Publication date: 1993-01-21
Also published as: AU2297992A

Abstract

The stack loader (221) is mounted on a tape drive (211) in the automated library system (111), between the library system robot (230) and the associated tape drive (211). The stack loader (221) receives a stack of data storage media cartridges, such as magnetic tape cartridges from the library system robot (230). The library system robot (230) retrieves a plurality of blank magnetic tape cartridges and loads these cartridges into the stack loader (221) to maintain an available set of scratch tapes ready for immediate loading in the tape drive (211). The library software (110) then translates scratch mount commands into control signals to activate the stack loader (221) to mount a scratch tape in the associated tape drive (211). With queued tape cartridges, the scratch loader (221) functions as a mechanical cache for preloading queued cartridges in the scratch loader (221) for immediate access by the tape drive (211).

Description

STACK LOADER ARRANGEMENT FOR AN AUTOMATED LIBRARY SYSTEM

FIELD OF THE INVENTION

This invention relates to automated library systems and, in particular, to an automated data storage media cartridge library system that includes an automated data storage media cartridge stack loader therein to reduce the mount times for scratch, batch loaded or queued data storage media cartridges.

PROBLEM

It is a problem in robotic data media retrieval systems to minimize the time required to load and unload magnetic tape cartridges on a tape drive. In the past, robotic tape cartridge systems loaded magnetic tape cartridges of the IBM 3480 type into a tape drive one magnetic tape cartridge at a time. The associated data processing system reads/writes data on the magnetic tape and, when the data transfer is completed, the tape drive ejects the magnetic tape cartridge. The tape drive remains in an idle state until the robot is notified that the magnetic tape cartridge is ejected, retrieves the ejected magnetic tape cartridge from the tape drive and replaces it with a new magnetic tape cartridge. This magnetic tape cartridge mount/dismount operation is time consuming, especially in an environment where the associated computer system sequentially requests a large number of tape cartridge mounts. The robot responds to the need for a tape cartridge mount/dismount faster than a human operator, but is still limited by having to process one magnetic tape cartridge at a time for each tape drive and by not being able to prestage a magnetic tape cartridge load.

SOLUTION

These problems are solved and a technical advance achieved in the field by the stack loader apparatus for an automated library system. The stack loader arrangement provides a significant improvement in data storage media cartridge mount times in an automatic data storage media cartridge library. The stack loader apparatus receives a stack of data storage media cartridges for mounting/dismounting in an associated media drive. An indexing mechanism on the stack loader translates the stack of data storage media cartridges in a downward direction so that the bottom most data storage media cartridge in the stack is in position in front of the media drive access port. A load mechanism in the stack loader inserts the bottommost data storage media cartridge into the media drive. When the data storage media cartridge is ejected from the media drive, it is loaded it onto an elevator mechanism in the stack loader that supports a stack of ejected data storage media cartridges.

This apparatus is especially advantageous for mounting scratch cartridge or a queued series of cartridges. The library system automatically retrieves a plurality of blank data storage media cartridges and loads these cartridges into the stack loader to maintain an available set of scratch data storage media cartridges ready for immediate loading into the associated media drive. The library software then translates scratch media mount commands into control signals to activate the stack loader to mount a scratch data storage media cartridge in the associated media drive. When the media drive finishes writing data, received from the associated computer system, on the scratch media, the stack loader places this data storage media cartridge into the eject stack for eventual retrieval and storage by the library system robot. Thus, the automated library system is able to retrieve used data storage media cartridges from the stack loader and load blank data storage media cartridges therein as a background process.

Similarly, data storage media cartridges can be prefetched by the automated library system when a sequence of data storage media cartridge mount requests are queued and scheduled to be read by a media drive. The stack loader then functions as a "mechanical cache" where the queued data storage media cartridges are prefetched and loaded in the desired sequence into the stack loader. The need to handle data storage media cartridges on an individual basis is thereby mitigated by the stack loader which enables the system to queue a plurality of data storage media cartridges for immediate loading on the associated media drive independent of the operation of the automated library system robot. This further enhances the performance of the automated library system by enabling the robot to intersperse prefetch mounts/dismounts with the more time critical read/write mounts/dismounts for other media drives. The automated library system thereby performs the time critical operations before the less time critical operations.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 illustrates the automated data storage media cartridge library system in block diagram form;

Figure 2 illustrates a top view of a library module;

Figure 3 illustrates a cut away view of a library module with its associated robot arm mechanism and data storage media cartridge storage cell array;

Figure 4 illustrates a perspective view of the robot arm mechanism;

Figure 5 illustrates a perspective view of the data storage media cartridge storage cells;

Figures 6 and 7 illustrate, in flow diagram form, the operational steps taken by the automated data storage media cartridge library system to select and transport a data storage media cartridge;

Figure 8 is a perspective view of the vision system and its source of illumination which are positioned at the end of the robot arm; Figure 9 illustrates, in flow diagram form, the sequencing of mount/dismount requests;

Figure 10 illustrates the automatic data storage media cartridge stack loader for tape drive systems in cut away perspective view; Figures 11 and 12 illustrate the automatic data storage media cartridge stack loader mechanism driving cam and data storage media cartridge load, insertion and unload apparatus;

Figures 13 through 15 illustrate the automatic data storage media cartridge stack loader mechanism data storage media cartridge insertion apparatus; and

Figure 16 illustrates the fully assembled housing for the automatic data storage media cartridge stack loader apparatus in perspective view. DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates in block diagram form the automated data storage media cartridge library system. A plurality of host computers 101, 102 are shown connected to the automated data storage media cartridge library system by means of two paths, a control path 161, 162 and a data path 171-175 described in more detail below. A plurality (up to sixteen) of host computers can be interconnected to a plurality (up to sixteen) of automated data storage media cartridge library systems, but only two computers and a single library system are illustrated for simplicity. The automated data storage media cartridge library system 100 consists of a plurality of elements. Among these elements are included two automated data storage media cartridge library modules (library modules) 111 and 112, each of which stores a plurality of data storage media cartridges, such as 18 track magnetic tape cartridges of the IBM 3480 type for use by host computers 101, 102. Each of library modules 111 and 112 stores up to 6,000 of the data storage media cartridges and contains a robot arm system that functions to retrieve the data storage media cartridges from media cartridge storage cells contained in the library module and load the retrieved data storage media cartridges on media drive systems, shown in Figure 1 as a plurality of elements 141-144 attached to each of library modules 111, 112. Any type of information storage volume can be used in this type of library system and magnetic tape cartridges are illustrated hereinbelow due to their widespread use in the data processing industry. Therefore, for the sake of simplicity, the following description refers to magnetic tape cartridges and tape drives although it is understood that any data storage media cartridge and corresponding media drive can be used to embody this invention as well as multiple types of media and drives in a single library system. A system of control elements 120, 121, 122, 123 are illustrated connected between host computer 101 and each library module 111, 112. The control elements illustrated in Figure 1 operate to control the robot arm mechanism in each of library modules 111 and 112. In operation, a user connected to host computer 101 requests access to data stored in a designated magnetic tape cartridge, which magnetic tape cartridge is stored in, for example, library module 111. Host computer 101 translates the request for this data into an operator console tape mount request message. Tape cartridge library software 109, 110 resides on host computers 102, 101 respectively and functions to interface the automated magnetic tape cartridge library system in transparent fashion to host computer 102, 101. This is accomplished by tape cartridge library software 110 which traps operator console messages from host computer 101 and converts these console messages into magnetic tape cartridge retrieval commands that are transmitted via data link 162 to library management unit 121.

Tape cartridge library software 110 contains a data base that provides the translation between magnetic tape cartridge volume records and the tape mount request operator console messages from host computer 101. Thus, a data retrieval request from host computer 101 is intercepted by tape cartridge library software 110 and used to scan the tape volume records to identify the exact physical location of the requested magnetic tape cartridge. Tape cartridge library software 110, determines the exact physical location of the requested magnetic tape cartridge in one of library modules 111 and 112 and the availability of one of tape drives 141-144 as well as the identity of the library module that contains the requested magnetic tape cartridge. Tape cartridge library software 110 then transmits control signals over path 161, via terminal control unit 120 and data link 162 to library management unit 121 to identify the exact location of the requested magnetic tape cartridge and the exact location of the destination tape drive.

Library management unit 121 responds to the exact physical location control signals from tape cartridge library software 110 by determining a path assignment from tape cartridge storage cell to the designated tape drive. For example, assume that the requested magnetic tape cartridge is located in library module 111 and the selected cartridge tape drive unit is 144 which is attached to library module 112. Library management unit 121 designates all of the functional steps to be taken by library modules 111 and 112 to effectuate the transfer of the requested magnetic tape cartridge from library module 111 to the selected tape drive unit 144 located on library module 112. These control signals are transmitted via control paths 163 and 164 to library control units 122 and 123 respectively. Library management unit 121 transmits control signals over control path 163 to library control unit 122 to identify the exact physical location of the requested magnetic tape cartridge. The robot arm in library module 111 is controlled by library control unit 122 which translates the control signals received from library management unit 121 into servo control signals to regulate the operation of the various servo systems (described below) of the robot arm in library module 111. Library control unit 122 causes the robot arm in library module 111 to retrieve the requested magnetic tape cartridge from the tape cartridge storage cell in library module 111.

The retrieved magnetic tape cartridge is transported by the robot arm in library module 111 to library module 112 by way of pass-through port 150 which is a device that interconnects two library modules 111, 112. The pass-through port is a mechanism that enables adjacent library modules to pass retrieved magnetic tape cartridges back and forth between the library modules for loading on a designated tape drive or for returning to the tape cartridge storage array. The pass-through port mechanism 150 that interconnects library module 111 with library module 112, in response to control signals from library control unit 122, rotates to face the robot arm in library module 111. The robot arm in library module 111, in response to the control signals from library control unit 122, places the retrieved magnetic tape cartridge in the reserved slot in pass- through port 150. Library management unit 121 upon the completion of the tape retrieval operation by library module 111, transmits control signals on control path 163 to library control unit 122 to activate pass-through port 150 to transport the retrieved magnetic tape cartridge to face the robot arm in library module 112. Library management unit 121 then transmits control signals on control path 164 to library control unit 123 associated with library module 112. Library control unit 123 responds to these control signals by generating servo control signals to regulate the operation of the robot arm in library module 112. These control signals cause the robot arm in library module 112 to retrieve the magnetic tape cartridge placed in pass-through port 150 by the robot arm in library module 111. The magnetic tape cartridge so retrieved by the robot arm in library module 112 is then placed by the robot arm in tape drive 144 as designated by library management unit 121. In this fashion, a data retrieval request from host computer 101 is translated into the identification of a designated magnetic tape cartridge, this magnetic tape cartridge is automatically retrieved from its storage rack and transported to a library module that contains an available tape drive. That library module then loads the retrieved magnetic tape cartridge into the tape drive where it can be read by host computer 101.

The automated tape cartridge library system 100 contains a separate data path completely independent and isolated from the control path described above.

The separate and independent data path consists of tape drive units 141-144, data paths 171-174, tape control unit 131 and data link 175. The retrieved magnetic tape cartridge is loaded onto tape drive 144 where it is read in the usual fashion, with the data output on lead 174 to tape control unit 131. The data from all the tape drives 141-144 is multiplexed together in tape control unit 131 and transmitted over data link 175 to host computers 101 and 102. Thus, the data read from the retrieved magnetic tape cartridge is transmitted from tape drive unit 144 through tape control unit 131 to host computer 101 without the automated tape cartridge library system

100 being aware of the destination of the data. In order to more fully understand the operation of the automated tape cartridge library system 100, additional details of the structure of library modules 111, 112 are disclosed below, as well as the control software in tape cartridge library software 110 and library management unit 121. Figure 2 illustrates a top view of the library module with the ceiling removed while Figure 3 illustrates a cut away side perspective view of library module 111.

Exterior Housing

Each library module 111 consists of a stand alone exterior housing which consists of a plurality of wall segments 221 attached to floor 312 and ceiling 311 plates and disposed about a vertical axis A. There is included an inner wall having a plurality of segments 231 forming upper portion which is suspended from a ceiling 311 of the library module 111 and another plurality of like segments 232 forming a lower portion of the interior wall which is mounted on the floor plates 312 to support a first cylindrical array 201 of tape cartridge storage cells centered about the vertical axis A. A second cylindrical array 202 of tape cartridge storage cells is concentrically arranged about the first array 201 and mounted on the wall segments 221 of the outer housing. A configuration of the segments 221 of the outer wall housing are such that the resulting structure is in the shape of a dodecahedron. The twelve-sided arrangement of the library module provides great flexibility in configuring both the tape drive units as well as configuring a plurality of library modules in a juxtaposed arrangement. Tape Cartridge Storage Cells

Library module 111 contains two concentrically arranged cylindrical arrays of tape cartridge storage cells 201, 202. Figure 5 illustrates in additional detail the arrangement of a particular array of tape cartridge storage cells. The array of tape cartridge storage cells illustrated in Figure 5 has a radius of curvature adapted to mounted in the inner cylindrical array 201 of tape cartridge storage cells of library module 111. The tape cartridge storage cells on the outer cylindrical array 202 are formed with an opposite curvature so that all of the tape cartridge storage cells in the inner 201 and outer 202 cylindrical arrays face each other so that the robot arm 230 can retrieve magnetic tape cartridges from either the inner 201 or the outer 202 cylindrical array. The tape cartridge storage cells illustrated in Figure 5 consist of a bottom portion 501, a back portion 502 with intervening wall segments 503 to provide a plurality of slots or cells for the storage of the magnetic tape cartridges. Bottom portion 501 of the tape cartridge storage cells is angled downward, front to back, so that a magnetic tape cartridge placed in the tape cartridge storage cell tends to slide along bottom portion 501 into the tape cartridge storage cell. The wall segments 503 are adapted for access by the hand and finger assemblies 240 of the robot arm 230. In addition, attachment apparatus such as hooks 504 formed at the rear of the array of tape cartridge storage cells can be used to suspend the tape cartridge storage cells from the wall segments of library module 111.

The arrangement of tape cartridge storage cells is illustrated more clearly in Figure 3 wherein the outer cylindrical array 202 is illustrated along the periphery of library module 111. The inner cylindrical array of tape cartridge storage cells 201 is illustrated in Figure 3 as comprising two individual segments. A first segment 302 of the inner cylindrical array is arranged as standing on the floor 312 of library module 111. A second segment 301 of the inner cylindrical array 201 is illustrated in Figure 3 as suspended from the ceiling 311 of the library module 111. In this fashion, an aperture is provided between the upper 301 and lower 302 segments of the inner cylindrical array 201 so that robot arm 230 can rotate about the center pivot axis "A" without interfering with any of the tape cartridge storage cells in the inner cylindrical array 201.

Robot Arm Mechanism

Figures 2, 3 and 4 illustrate a top view, side view and perspective view respectively of the robot arm assembly 230 of library module 111. The robot arm assembly 230 consists of a plurality of mechanisms all operating in conjunction to provide a movable arm for retrieving magnetic tape cartridges from their individual storage cells. The robot arm is described in detail in United States Patent Serial No. 4,864,511 issued September 5, 1989. The robot arm is discussed herein to illustrate the operation of this embodiment of the invention. The robot arm 230 consists of an arm assembly including a theta arm 321 rotatably mounted on a support column 322 which is attached to the floor plates 312 of library module 111. The arm assembly includes a Z mechanism 323 attached to the end of theta arm 321 remote from the support column 322. The Z mechanism 323 has coupled thereto a wrist, roll and finger assemblies 240 which perform the actual magnetic tape cartridge retrieval from the storage cell function. The Z mechanism 323 provides a vertical range of motion for the wrist, roll and finger assemblies 240 to access various levels of the tape cartridge storage cell array. The theta arm 321 locates the z mechanism 323 and its associated wrist, roll and finger assemblies 240 in the proper location to access both the inner 201 and outer 202 cylindrical arrays of tape cartridge storage cells. The robot arm support column 322 includes a motor which causes the theta arm 321 of the robot arm 230 to rotate about the pivotal point "A" of the robot arm 230 so that the robot arm 230 can access all of the tape cartridge storage cells in the circular array about the pivot point A. Thus, the elements in the robot arm assembly 230 cooperatively operate to access each and every storage cell in the entire library module 111. The servo motors controlling each of the various ranges of motion associated with elements in the robot arm assembly 230 are all controlled by control unit 122 connected to library module 111. Suffice it to say that the robot arm assembly 230 is operational to retrieve a magnetic tape cartridge from any of the approximately 6,000 tape cartridge storage cells in library module 111.

Vision System

A vision system 1201 located on the wrist (roll) assembly is illustrated in Figure 1. Vision system 1201 is located on the top of the wrist assembly and is focused on a rectangular-shaped area a predetermined distance in front of the finger assembly when the finger assembly is fully retracted. The point of focus of vision element 1210 coincides with the position of a machine-readable label imprinted on the end of the magnetic tape cartridge stored in a magnetic tape cartridge storage cell. This focus is such that the vision element can read both the label imprinted on the end of the magnetic tape cartridge that is stored in the tape cartridge storage cell as well as a positioning target associated with the tape cartridge storage cell. In order to enable vision element 1210 to read the label on the magnetic tape cartridge, a source of illumination is provided. The source of illumination consists of pair of lamps 1211, 1212 arranged one on either side of vision element 1210, and aligned in substantially the same orientation as vision element 1210. Lamps 1211 and 1212 are directed so that the light beams emanating from these two lamps illuminate a rectangular-shaped area in the line of sight of vision element 1210, which area coincides with the position of the label on the end of the magnetic tape cartridge. Thus, the illumination provided by the two lamps 1211 and 1212 is evenly distributed across the label on the magnetic tape cartridge so that vision element 1210 can accurately read the machine readable characters imprinted on the label.

Tape Drive Unit

The magnetic tape cartridges retrieved from the individual tape cartridge storage cells are typically loaded onto a tape drive (ex 211) so that the data contained on the magnetic tape stored in the magnetic tape cartridge can be read by host computer 101. Figure 2 illustrates the placement of two tape drive units 141, 142 on library module 111. The tape drive units are shown attached to two of the twelve outside walls of library module ill. Within each tape drive unit (ex 141) is located a plurality of individual tape drives 211, 213 which function to read data from the magnetic tape cartridges loaded therein. Figure 2 illustrates a single tape drive (211) and its associated stack loader 221 located in the tape drive unit 141 to illustrate the orientation of tape drive 211, stack loader 221 and tape drive unit 141 with respect to the robot arm 230 and the cylindrical array of tape cartridge storage cells. In particular, a segment of the tape cartridge storage cells is removed from outer cylindrical array 202 to provide an aperture through which the front loading door opening of stack loader 221 (connected to tape drive 211) protrudes a sufficient distance so as to be lined up with the surrounding storage cell arrays. The robot arm 230 can thereby load or unload a magnetic tape cartridge into stack loader 221 with the same or similar range of motion as the replacement of a magnetic tape cartridge into one of the individual storage cells in the tape cartridge storage cell arrays. A side view of tape drive unit 141 is shown in Figure 3 wherein two of the tape drives 211, 213 and their associated stack loaders 221, 223 are shown stacked one above the other in a vertical alignment within tape drive unit 141 illustrated in Figure 2. As can be seen from Figures 2 and 3 the orientation of the stack loaders 221, 223 and their respective tape drives 211, 213 is such that a magnetic tape cartridge is placed into the stack loader (ex 221) on an angle similar to that of the individual tape cartridge storage cells with the difference being that the stack loader 221 requires a horizontal loading of the magnetic tape cartridge while the tape cartridge storage cells store the magnetic tape cartridges in a vertical alignment. Thus the robot arm 230 in retrieving a magnetic tape cartridge from an individual tape cartridge storage cell and loading it into a tape drive unit 141 must rotate the magnetic tape cartridge through a 90 degree angle for proper orientation for loading into the tape drive 211.

Tape Cartridge Library Software Architecture Figure 7 illustrates in block diagram form the architecture of library software 110 which resides in host computer 101. The library software architecture is divided into two segments, a first segment 1001 consists of software routines located in the user's address space of host computer 101, while the second portion 1002 consists of software components that are located in the host computer address space. The software is divided up into these two segments in order to provide an interface between the host computer 101 and the automated tape cartridge library system 100 that is transparent to the host computer 101. This is accomplished by providing software routines in the host computer access space, which routines intercept the normal control messages that the host computer 101 sends to the operator console. These control messages are then used to activate the automated tape cartridge library system 100. This software also provides data flow in the reverse direction in the form of console messages to indicate to the host computer 101 that the particular requested operation has been completed. In this fashion, the host computer 101 need not be modified in order to support the installation of the automated tape cartridge library system 100.

In order to accomplish this function, a number of software routines are provided in the host software component architecture. These software routines include configuration control 1011, which provides coordination and control of the automated cartridge library system which is used to store data to identify tape cartridge volume numbers and the physical location of each magnetic tape cartridge. Data base server 1012 provides control of the library control data base itself. LMU server 1013 provides a communication interface for each of the library module units 121 in the automated tape cartridge library system 100. Allocation software module 1014 translates a request for a magnetic tape cartridge mount or dismount to take place into the identification of a particular available tape drive in the automated tape library system 100. Job processing software component 1015 traps console messages and converts these messages into control messages which are transmitted to the mount/dismount software component 1016. The mount/dismount software component 1016 receives these control messages and performs the requested magnetic tape cartridge mount or dismount operation by transmitting control signals through LMU server 1013 to the particular library management unit 121 associated with the selected automated tape cartridge library system 100. In addition, utility software 1016 and administration software 1018 are provided to generate administrative reports on the operation of the library resources as well as to provide maintenance installation and control interfaces with the operator console. Allocation

In order to more fully understand the operation of tape cartridge library software 110, a typical magnetic tape cartridge mount request operation is described in detail. This description assumes a library system that stores and retrieves only magnetic tape cartridges in order to avoid the complexity required to describe a multi-media library, which is not relevant to the basic teaching of this invention. This operation begins when a user on one of the host computer systems, such as 101, requests access to a particular set of data which is stored on a magnetic tape cartridge located in library module 111. This request for access to a magnetic tape cartridge enters host computer 101 either through a console message from the host computer operator or from a user connected to host computer system 101 via one of a plurality of data terminals (not shown) connected thereto. The host computer 101 responds to the request for a magnetic tape cartridge by invoking allocation processing and by providing the name of the data set requested, the volume serial number of the magnetic tape cartridge and identification of the type of device that the data set is to be mounted on. The tape cartridge library software 110 intercepts this allocation request and gains control of the allocation operation. Tape cartridge library software 110 by way of configuration software 1011 and data base server 1012 searches the library data base to determine which cartridge storage slot in library module 111 contains the requested magntic tape cartridge. This is done by reviewing the data tables stored in the tape library to obtain the correspondence between the magnetic tape cartridge volume serial number and the physical location of the magnetic tape cartridge in library module 111. Figure 11 illustrates in flow diagram form the operation of the tape cartridge library software allocation operation. As step 1101, tape cartridge library software 110 determines whether a specific tape drive unit address was specified. If an exact address was specified, the allocation process need proceed no further since a tape drive had already been designated. Processing then proceeds to exit back to the host computer operating system. Assume for the purpose of this discussion that a specific unit address was not specified, then host software component processing advances to step 1102 where the determination is made of whether the requested device type is a magnetic tape cartridge drive or not. If the requested unit is not a magnetic tape cartridge drive, then the requested unit would not be part of the automated tape cartridge library system 100 and processing again would exit this particular subroutine. Assume again for the purpose of this description that the required unit is a magnetic tape cartridge drive, then processing advances to step 1103 where a determination is made of whether a specific magnetic tape cartridge volume was requested. If a specific magnetic tape cartridge volume is requested, processing advances to 1104 where the tape cartridge volume number is translated into a six-character volume serial number, known as VOLSER. Processing then advances to step 1105 where the volume location conversion operation is invoked. This operation requires a table look-up to convert the six-character VOLSER into an exact physical location of the magnetic tape cartridge in library module 111. Once this conversion has been completed, processing advances to step 1106 where determination is made of whether the volume is in library module 111. If it is not, processing advances to step 1107 where a message is generated to indicate that the magnetic tape cartridge is not stored in the automated tape cartridge library system 100 but is available elsewhere and can be retrieved by means of an operator manually retrieving the magnetic tape cartridge volume and loading it into a manual load tape drive unit. Processing then exits back to the operating system of host computer 101. For the purpose of this description, assume that the volume is in library module 111. Processing then advances to step 1108 where a unit name is substituted for the generic tape drive request. What this means is that a particular tape drive is identified by tape cartridge library software 110 as being available in automated tape cartridge library system 100 and this tape drive is the one in which the requested magnetic tape cartridge will be mounted so that data can be retrieved by host computer 101.

An alternative situation is where at step 1103 a specific tape cartridge volume is not requested. In this case, processing advances to step 1109 where a determination is made of whether the type of volume requested is a library scratch volume; that is, a blank magnetic tape cartridge stored in library module 111 available to be used by any of the users of host computer 101. If a scratch volume is not requested, then an error has occurred and processing is aborted and control is returned to the operating system of host computer 101. If a scratch volume is requested, processing advances to step 1110 where a routine is invoked to determine the location of scratch tape cartridge volumes in the automated tape cartridge library system. This routine maintains a list of all scratch magnetic tape cartridges in the entire automated tape cartridge library system. Once a particular scratch tape cartridge volume has been located and designated as available for use, processing advances again as before to step 1107 where a particular available tape drive is identified.

Tape cartridge library software 110 has, therefore, intercepted the invocation of the host computer allocation process and has provided its own resource allocation in transparent fashion so host computer 101 is not aware of the fact that an automated magnetic tape cartridge library system 100 is connected to host computer 101. What tape cartridge library software 110 returns to host computer 101 at the end of the above-described processing, is an identification of the particular magnetic tape cartridge drive that is available for mounting the requested magnetic tape cartridge. Host computer 101 proceeds with its processing until it is ready to request that the particular magnetic tape cartridge be mounted.

Volume Mount Operation When host computer 101 requests that a designated magnetic tape cartridge be mounted, tape cartridge library software 110 intercepts this console command and activates job processing software 1015 which, through LMU server software 1013, insures that the tape cartridge drive is available. If the tape cartridge drive is available, job processing software 1015 transmits robot arm control commands through LMU server software 1013 package which transmits these commands to the 3274 terminal control unit (120) which acts as a protocol converter interface between host computer 101 and library management unit 121. The 3274 terminal control unit 120 converts the control messages received from host computer 101 into a format that is compatible with library management unit 121 and transmits these adapted control messages over a data link 162. Library management unit 121 is configured to look like a 3278 Model 2 terminal and, therefore, requires a 3274 terminal control unit to be interposed between the host computer 101 and the library management unit 121. Library management unit 121 takes the control messages transmitted from host computer 101 by way of tape cartridge library software 110 and adapts these commands to operate the robot arm in library module 111.

The control messages received from tape cartridge library software 110 and library management unit 121 consists of an information storage volume or magnetic tape cartridge mount command, an indication of which library module 111 the magnetic tape cartridge resides, its exact physical location in library module 111, where the physical location is designated by a panel in the tape cartridge storage array and a row/column indication of where on this particular panel the magnetic tape cartridge is stored. Library management unit 121 utilizes the received control signals to position the robot arm so that the retrieval mechanism, the robot hand is positioned to the correct panel/row/column location associated with the designated magnetic tape cartridge to be retrieved. The vision system on the robot arm examines the identification label on the magnetic tape cartridge and when the identification is verified as matching that indicated by host computer 101, the robot hand is extended, the magnetic tape cartridge is grasped and removed from the storage cell in which it has been placed. The robot hand extracts the magnetic tape cartridge and once the magnetic tape cartridge has cleared the side of a particular storage cell, the robot mechanism is relocated to an alignment with the designated tape drive. Library management unit 121 signals library module 111 to insert the retrieved magnetic tape cartridge into the tape transport and the robot hand is extended and the magnetic tape cartridge placed in the tape transport. The hand is then retracted and the robot arm is available for any other magnetic tape cartridge retrieval operation. Once the robot arm loads the magnetic tape cartridge in tape drive 211, tape control unit 131 interconnects tape drive 211 with host computer 101 by way of data paths 175 and 173.

Tape control unit 131 manages the writing and reading of data to and from the attached tape transport mechanisms 141-144. Tape control unit 131 can be connected to up to four tape drive units 141-

144 each of which can contain up to four tape drives.

Thus a tape control unit 131 can interconnect up to sixteen tape drives with the host computer 101. The data path 175 interconnects tape control unit 131 with host computer 101 contains four data channels. Tape control unit 131 receives commands from host computer

101 over these four data channels, decodes these commands and selects tape drives and issues commands to them, and passes data from the channel to the transports and vice versa. Thus, tape control unit

131 functions as a multiplexer interconnecting the sixteen tape drives to the four channels connected to the host computer. Data and control and status signals are passed back and forth between host computer and the tape drive units by way of tape control unit 131. In addition, tape control unit 131 contains a data buffer which is a first end first out dynamic random access memory connected between the four data channels 175 connected to the host computer 101 and the tape drives located in the tape drive units 141-144. The data buffer masks the inherent slowness of a mechanical tape drive system and permits data transfers to and from the automated tape cartridge library system at data channel speeds. In addition, while data to and from the transport flows at a rate proportional to the speed of the moving magnetic tape on a magnetic tape cartridge, the channel can begin writing data to this data buffer while the magnetic tape is coming up to speed. The channels can write in the data buffer the data it wants to transfer, disconnect from the connection, leaving the data buffer to send data to the tape drive without further involvement of the channel. In the reverse direction, a channel waits until all or most of the data from the file stored on the magnetic tape cartridge is in the data buffer and reconnects to the channel and transfers the data to host computer 101.

Stack Load Apparatus Architecture

The automatic magnetic tape cartridge stack loader apparatus is illustrated in perspective view in Figure 10. This apparatus is contained in a housing that consists of a top plate 1113, back plate 1114 and floor plate 1115. Three cover plates (not shown) are attachable to the top plate 1113, back plate 1114 and floor plate 1115 illustrated in Figure 10 to completely enclose the automatic magnetic tape cartridge stack loader apparatus contained in the housing. Figure 16 illustrates the completely assembled housing including a plurality of magnetic tape cartridges 701 inserted into stack load slot 1100. The housing and its included apparatus is placed in front of a tape drive 702. The tape drive has an access port into which a magnetic tape cartridge can be placed by an operator or by the automatic magnetic tape cartridge stack loader apparatus. Back plate 1114 has an opening therein that matches the size, shape and position of the access port of the associated tape drive 702. Back plate 1114 is placed in juxtaposed position with the front of the tape drive 702 such that the automatic magnetic tape cartridge stack loader apparatus can load a magnetic tape cartridge through the opening in back plate 1114 into the access port of the tape drive 702 as is described below. The automatic magnetic tape cartridge stack load apparatus includes a stack load slot 1100 into which a plurality of magnetic tape cartridges can be inserted in a single operation. The stack load slot 1100 is bounded on two sides by stack grab plates 1101, 1102. These plates 1101, 1102 are moveable in the horizontal direction (illustrated by arrow C) to come into contact with the stack of magnetic tape cartridges loaded in stack load slot 1100 and to securely hold the stack of magnetic tape cartridges in a clamping operation. Drop mechanism 1103 is located below stack grab plates 1101, 1102 and serves to provide a bottom portion to the stack load slot 1100. Drop mechanism 1103 consists of a pair of moveable angular shaped fingers which, when in the closed position, provide a lip or shelf on the lower right hand and lower left hand portions of stack load slot 1100. This shelf provides support for the bottom of the stack of magnetic tape cartridges that are inserted into magnetic tape stack load slot 1100. The two fingers of drop mechanism 1103 are operated to be moved in the downward direction (illustrated by arrow A) , then in the outward direction (illustrated by arrow C) where they swing apart a sufficient distance so that a magnetic tape cartridge from the bottom of the stack in magnetic tape cartridge stack load slot 1100 down can be deposited onto tray mechanism 1104, located below drop mechanism 1103.

Drop Mechanism In operation, stack grab plates 1101, 1102 are maintained in the extended position where they do not come in close contact with magnetic tape cartridges loaded in magnetic tape cartridge stack load slot 1100. Drop mechanism 1103 is maintained in the closed position to thereby provide support for the bottom of the stack of magnetic tape cartridges in stack load slot 1100 to prevent the magnetic tape cartridges loaded therein from dropping below. Thus, an operator loads a plurality of magnetic tape cartridges into the stack load slot 1100, which magnetic tape cartridges are to be sequentially loaded into the associated tape drive. To load a magnetic tape cartridge into the tape drive, motor 1123 is activated to rotate worm shaft 1124 which engages and turns cam 1125. Figure 11 illustrates a front view of cam 1125 and drop mechanism 1103 as viewed in direction B shown on Figure 10. The initial position of drop mechanism 1103 is as shown in Figure 10 where the shelf or fingers of drop mechanism 1103 are located at the bottom of stack grab plates 1101, 1102. This position corresponds to the position noted by "A" in Figure 11. As motor 1123 turns cam 1125, the vertical and horizontal positions of drop mechanism 1103 are changed. Cam 1125 rotates about pivot point 1131. Cam 1125 includes a plurality of tracks such as 1132. Crank 1133 includes a follower 1134 that is positioned in track 1132. Levers L and R are also each connected at one end to crank 1133 by pivots 1136 and 1138 respectively. Levers L and R are connected at their respective other ends to the left side and right side of drop mechanism 1103 by pivots 1135 and 1139 respectively. As cam 1125 rotates about pivot point 1131, follower 1134 moves along track 1132. The combined motion of follower 1134 along with the shape of crank 1133 causes drop mechanism 1103 to translate in vertical and horizontal directions. Drop mechanism 1103 first moves from position A to position B in a downward vertical direction. Load mechanism 1104 also has angular shaped fingers at its top end to provide a shelf that has notches 1117 cut into it. These notches 1117 provide openings into which the fingers of drop mechanism 1103 fit when drop mechanism 1103 is translated into position B by cam 1125. Thus, the bottommost magnetic tape cartridge in the stack located in stack loader slot 1100 is supported by the shelf of load mechanism 1104 rather than the shelf of drop mechanism 1103 when drop mechanism 1103 is in position B.

Stack grab plates 1101, 1102 are operated by cam 1125 concurrently with drop mechanism 1103. Figure 12 illustrates the mechanism to activate stack grab plates 1101, 1102. A second track 1303 on cam 1125 is used to clamp the sides of the stack of magnetic tape cartridges in stack load slot 1100 as the stack is being displaced in a downward direction by drop mechanism 1103. Crank 1301 is activated by follower 1302 in track 1303 to cause clamp lever 1118 to engage stack grab plate 1101 to translate stack grab plate

1101 toward stack grab plate 1102, thereby clamping the sides of the stack of magnetic tape cartridges in stack load slot 1100. The stack is clamped such that stack grab plates 1101, 1102 clamp all of the magnetic tape cartridges in the stack except the bottom most magnetic tape cartridge. In addition, the timing of the operation of stack grab plates 1101, 1102 is coordinated with the operation of drop mechanism 1103 such that the stack is clamped before drop mechanism 1103 completes its downward motion. Therefore, when drop mechanism 1103 reaches position B of Figure 11, there is a gap between the top of the magnetic tape cartridge now resting on the shelf of load mechanism 1104 and the bottom of the bottom most magnetic tape cartridge in the stack.

Stack grab plates 1101 and 1102 securely hold the stack of magnetic tape cartridges with the exception of the bottom most magnetic tape cartridge so that the remaining stack of magnetic tape cartridges cannot move. Once cam 1125 operates stack grab plates 1101,

1102 to securely and firmly grasp the stack of magnetic tape cartridges in magnetic tape cartridge stack load slot 1100, cam 1125 operates drop mechanism 1103 to move in the outward direction out from under the bottom of the bottom most magnetic tape cartridge in the magnetic tape cartridge stack. Once drop mechanism 1103 has been rotated a sufficient distance outward to position C of Figure 11, it no longer provides vertical support to the bottom most magnetic tape cartridge. This magnetic tape cartridge is supported only by the shelf of load mechanism 1104 which is in the closed or supporting position. Cam 1125 continues to rotate and operates drop mechanism 1103 in the reverse direction to move vertically to position D and then to come together and close under the bottom of the remaining magnetic tape cartridge stack into position A, the starting position or closed position. Once drop mechanism 1103 is in the closed position, cam 1125 operates stack grab plates 1101, 1102 to move outwardly to release the magnetic tape cartridge stack. The magnetic tape cartridges in the stack are now again supported by the closed drop mechanism 1103. Thus, stack grab plates 1101, 1102 drop mechanism 1103 and load mechanism 1104 operate as described above to deposit the magnetic tape cartridge that is on the bottom of the stack into position in front of the access port of the associated tape drive 1702 to be loaded therein.

Tractor Mechanism

The magnetic tape cartridge, located on the shelf of load mechanism 1104, is placed into the access port of the associated tape drive by the operation of a tractor mechanism 1126 (Figure 13) that is part of the automatic magnetic tape cartridge stack loader apparatus. This tractor mechanism 1126 consists of a drive belt 1105 which is pivoted into position (Figure 14) by the cranks and pivots 1501-1508 of the tractor mechanism 1126 to come into contact with one side of the magnetic tape cartridge that has been deposited on the shelf of load mechanism 1104. Drive belt 1105 is thereby clamped against one side of the magnetic tape cartridge while the other side of the magnetic tape cartridge rests against a friction plate 1509 that has a low coefficient of friction and is located on the opposite side of the magnetic tape cartridge. Drive belt 1105 is operated by a motor 1131 to rotate in a counterclockwise direction as viewed from above to slide the magnetic tape cartridge from the shelf of load mechanism 1104 through the opening in back plate 1114 into the access port of the corresponding tape drive.

Tractor mechanism 1126 includes drive belt 1105 which is driven by drive gear 1511 of motor 1131 to follow a path around pulleys 1509, 1510, 1512. Drive belt 1105 slides the magnetic tape cartridge into and out of the access port of the associated tape drive 1702, depending on the direction of rotation of motor 1131. The tractor mechanism is pivoted into position by the operation of cranks 1501-1503 and pivots 1504- 1508. Figure 13 illustrates the position of cranks 1501-1503 when tractor mechanism 1126 is in the retracted position. Motor 1129 drives gear 1130 which turns threaded screw 1601 to reposition cranks 1501- 1503. This is accomplished by the rotation of threaded screw 1601 translating nut 1602, which is attached to spring 1106 in direction A. The spring 1106 is compressed by nut 1602 and exerts a force on frame 1108 of tractor mechanism 1126, causing cranks 1501-1503 to pivot and reposition drive belt 1105 into position against one side of the magnetic tape cartridge. Motor 1129 keeps rotating until drive belt 1105 is positioned against the side of the magnetic tape cartridge and spring 1106 is also compressed.

In order to ensure that the magnetic tape cartridge is properly seated in the tape drive, tractor mechanism 1126 also acts as a kicker mechanism (Figure 15) to push the back of the magnetic tape cartridge so that the magnetic tape cartridge is inserted all the way into the tape drive. The kicker operation is implemented when drive belt 1105 slides the magnetic tape cartridge into the associated tape drive 1702. Once the magnetic tape cartridge clears the end of tractor mechanism 1126, spring 1106 further operate cranks 1501-1503 and pivots 1504-1508 to swing drive belt 1105 out into the opening behind the magnetic tape cartridge that has been inserted most of the way into the tape drive slot by drive belt 1105. Thus, tractor mechanism 1126 drive belt 1105 is positioned behind the magnetic tape cartridge so that the end of drive belt 1105 presses against the outwardly facing end of the magnetic tape cartridge. Tractor mechanism 1126 continues its rotation due to spring 1106 so that the end of drive belt 1105 pushes the magnetic tape cartridge into the associated tape drive 1702.

Magnetic Cartridge Eject

Once the tape drive has completed the read or write of data on this magnetic tape cartridge, the tape drive ejects the spent magnetic tape cartridge out onto load mechanism 1104. A reverse sequence of operations now takes place to unload the magnetic tape cartridge from the tape drive. Drive belt 1105 is operated in the position shown in Figure 14 in the clockwise direction to remove the magnetic tape cartridge from the tape drive and retrieve it all the way onto load mechanism 1104. Once this has taken place, solenoid 1127 operates load mechanism 1104 to rotate its two fingers in the outward direction so that the magnetic tape cartridge resting on the top of load mechanism 1104 is placed into the spent cartridge retrieval mechanism. The spent cartridge retrieval mechanism consists of a slot 1111 that has two sides 1110 in a fixed position so that the slot 1111 is slightly wider than a magnetic tape cartridge. An elevator mechanism 1112 is provided to move in a vertical direction (A) such that the elevator mechanism 1112 is located immediately below load mechanism 1104 so that the magnetic tape cartridge is placed on to elevator mechanism 1112 once load mechanism 1104 operates in the outwardly direction. Elevator mechanism 1112 is positioned a sufficient distance below the bottom of load mechanism 1104 so that the spent magnetic tape cartridge can rest on the top of elevator mechanism 1112 and not interfere with the operation of load mechanism 1104. With each new magnetic tape cartridge that is ejected from the tape drive and placed by load mechanism 1104 onto the top of elevator 1112 or the stack of magnetic tape cartridges resting on the top of elevator mechanism 1112, motor 1121 and power screw 1128 reposition elevator mechanism 1112 down one additional magnetic tape cartridge width below load mechanism 1104 so that the subsequent ejected magnetic tape cartridge placed on the top of the existing stack of magnetic tape cartridges supported by elevator mechanism 1112 clears load mechanism 1104.

Thus, it can be seen that this apparatus enables an operator to load an entire stack of magnetic tape cartridges into the magnetic tape cartridge stack load slot 1100. No individual placement of magnetic tape cartridges is required and the slot can continuously be refilled at the operator's convenience to thereby maintain a continuous feed of magnetic tape cartridges into the associated tape drive. Similarly, the loader apparatus stacks ejected magnetic tape cartridges in a stack on the bottom portion of load mechanism 1104 so that they can be retrieved by the operator, not on an individual basis, but as an entire stack. This stack loading and retrieval provides a more efficient operation than the individual loading of magnetic tape cartridges into an automatic loader apparatus. One additional benefit of this apparatus is that it can be operated in a bidirectional fashion. Thus, the ejected magnetic tape cartridge that is top most on the stack of ejected magnetic tape cartridges on top of elevator mechanism 1112 can be reloaded into the associated tape drive. This accomplished by solenoid 1127 operating load mechanism 1104 so that its fingers are in the outward direction. Elevator mechanism 1112 is moved vertically to bring the upper most magnetic tape cartridge in the stack of ejected tape cartridges in position in front of the opening in the associated tape drive. Load mechanism 1104 is then operated to close so that its fingers slide under the bottom of the top most magnetic tape cartridge in the ejected tape cartridge stack. The magnetic tape cartridge so repositioned is now ready to be loaded into the associated tape drive as described above where the magnetic tape cartridges that are dropped from above from the magnetic tape cartridge stack load slot 1100. Thus, the last written or read magnetic tape cartridge can be reloaded into the tape drive for further reading or writing of data thereon.

Processing Cartridge Mount/Dismount Requests

Figure 9 illustrates in flow diagram form the operational steps taken by the automated data storage media cartridge library system 100 to process cartridge mount/dismount requests received from host computer 101, 102. At step 901, the automated library system 100 receives a data storage media cartridge mount or dismount request from one of the associated host processors 101, 102. This request is converted as noted above into a library volume movement management command. Prior to generating the specific robot control commands that are necessary to regulate the movement of the automated library system robot 230, a determination must be made of the nature of the received mount/dismount request. This determination is illustrated in Figure 9 in steps 902-907 and consists of a routine that distinguishes between stack loader service requests and requests for conventional tape drives.

In particular, at step 902, the control software determines whether there are any pending mount/dismount requests for conventional tape drives or stack loaders. If there are no pending mount/dismount requests, processing advances to step 907 where the received mount/ ismount request for the stack loader is immediately processed. If however at step 902 there are pending mount/dismount requests the automated library system 100 preferentially services requests for conventional tape drives. As noted above, the performance of the automated library system 100 is advanced by deferring the stack loader mount/dismount requests in favor of the conventional tape drive mount/dismount requests since the stack loader apparatus is typically used to prestage or batch process a plurality of magnetic tape cartridges and therefore does not need immediate service to load to unload one of the prestaged magnetic tape cartridges into the associated tape drive. The stack loader apparatus is filled with additional magnetic tape cartridges or spent magnetic tape cartridges are removed therefrom as a background process by the automated library system robot 230 unless the stack loader apparatus is without any queued magnetic tape cartridges or has the eject bin thereof completely filled with spent magnetic tape cartridges and can no longer service the associated tape drive. In those cases, the stack loader is treated as a conventional tape drive.

Therefore, at step 902 processing of conventional tape drive mount/dismount requests are preferentially handled. If the requests received from the host processor has as its target a stack loader equipped tape drive, processing advances to step 903 to determine whether the target stack loader is in need of immediate service since it either has no additional magnetic tape cartridges in the load mechanism or has a completely full eject mechanism. In this case, the associated tape drive is no longer operational and the stack loader receives equal priority with the conventional tape drives. Therefore, if the stack loader is idle and there are no outstanding conventional tape drive mount/dismount requests, processing advances to step 907 where the request is immediately handled in order to maintain the operational status of the tape drive associated with the stack loader.

If the stack loader is not idle and there have been pending mount/dismount requests, then at step 905 one of the pending mount/dismount requests is serviced in the order of arrival since this scratch loader can continue servicing its associated tape drive and it does not require immediate serving of its mount/dismount request. Upon the conclusion of the serving operation, at step 906 a determination is made whether there are additional mount/dismount requests received from the host processor in the time interval that it took to process the previously received request. If there is not a new request, processing returns to step 902 to determine whether there are any pending or queued mount/dismount requests in order to execute the backlog of service requests in an orderly fashion. If there is a new request processing advances to step 901 where the original receipt of this request and its analysis is processed as described above.

The distinction between stack loader and conventional tape drive service requests enables the automated library system 100 to use the stack loaders as a mechanical cache wherein a number of magnetic tape cartridges can be prestaged for sequential processing by the associated tape drive while conventional tape drives are serviced in an immediate fashion since they are idle once a tape must be mounted or dismounted therefrom. The prestaging of the magnetic tape cartridges in the stack loader is handled as a background process, interspersed in the idle times betweenprocessing immediate mount/dismount requests for conventional tape drives. This is especially beneficial when the stack loader is used a scratch tape mount facility and a plurality of scratch tapes can be prestaged in the stack loader. This enables the host processor to continually write data onto magnetic tape cartridges and to dismount written magnetic tape cartridge from the associated tape drive and load another scratch tape therein. This stack loader tape load operation execution time is a fraction of the time that it would take the automated library system 100 to locate, retrieve, transport and mount a scratch tape from one of the tape cartridge storage locations therein to the particular tape drive requesting the scratch tape. The stack loader equipped tape drive can sequence through a series of magnetic tape cartridges faster than it could if serviced by the library robot alone and the library robot can service the remaining tape drives in a shorter time interval then if all of the tape drives on the system were not equipped with the stack loader. The stack loader therefore provides a significant service improvement in the automated library system since it provides the library system with a time management capability that results in a direct significant service improvement.

While a specific embodiment of the invention has been disclosed, it is expect that those skilled in the art can and will implement variations of the preferred embodiment disclosed therein, which variations still fall within the scope of the appended claims.

Claims

I CLAIM:

1. A data storage media cartridge handling system connected to at least one associated host computer (101) for robotically storing and retrieving a plurality of data storage media cartridges therein comprising: an array (201, 202) of data storage media cartridge storage locations, each for storing an associated data storage media cartridge; at least one media drive means (211) connected via a data link (171) to said host computer (101) and located juxtaposed to said array (201, 202) of data storage media cartridge storage locations for reading/writing data onto a data storage media cartridge loaded therein; stack loader means (221) attached to said media drive means (211) for automatically storing a plurality of data storage media cartridges and loading said plurality of data storage media cartridges in sequence in said media drive means (211) ; and robot means (230) for transporting said data storage media cartridges between said data storage media cartridge storage locations and said stack loader means (221) .

2. The system of claim 1 wherein said array (201,202) of data storage media cartridge storage locations includes: a first cylindrical array (202) of data storage media cartridge storage locations centered about a vertical axis (A) .

3. The system of claim 2, wherein each of said data storage media cartridge storage locations in said cylindrical array (202) includes a front opening that is inwardly directed in a radial direction toward said vertical axis (A) to accept data storage media cartridges to be stored therein, said robot means

(230) includes: a support column (322) centered on said vertical axis (A) ; arm means (321) connected to said support column (322) and rotatable around said vertical axis

(A) ; and means (240) connected to the distal end of said arm means (321) for retrieving said data storage media cartridges stored in said first cylindrical array (202) .

4. The tape cartridge handling system of claim 3 wherein said array (201, 202) of data storage media cartridge storage locations further includes: second cylindrical array (201) of data storage media cartridge storage locations concentrically arranged inside of said first cylindrical array (202) wherein said front opening of said data storage media cartridge storage locations in said second cylindrical array (201) are outwardly directed in said radial direction.

5. The system of claim 4 wherein said retrieving means (240) are positioned between said first cylindrical array (202) and said second cylindrical array (201) .

6. The system of claim 1 wherein said stack loader means (221) includes: means (1104, 1126) for loading a data storage media cartridge into said media drive means (211) ; and means (1100-1103) located in juxtaposed position above said loading means (1104) for receiving a stack of data storage media cartridges placed therein by said robot means (230) and operable to deposit the bottommost data storage media cartridge of said stack into said loading means (1104, 1126) for insertion into said media drive means (211) .

7. The system of claim 6 wherein said stack loader means (221) further includes: means (1112) located in juxtaposed position below said loading means (1104, 1126) for receiving data storage media cartridges ejected by said associated media drive means (211) into said loading means (1104,1126).

8. The apparatus of claim 7 wherein said loading means (1104, 1126) includes: means (1104) for supporting a data storage media cartridge ejected from said media drive means (211) above said receiving means (1112) .

9. The apparatus of claim 8 wherein said supporting means (1104) is operable to place said ejected data storage media cartridge into said receiving means (1112) .

10. The system of claim 1 further comprising: means (120-122) , responsive to a user on said associated host computer (101) requesting a scratch data storage media cartridge, for activating said stack loader means (221) to load one of said data storage media cartridges stored in said stack loader means (221) into said media drive means (211) .

11. The system of claim 1 further including: means (120, 121) , responsive to a data storage media mount/dismount request presently received from said host processor (101) which directs said data storage media handling system robot means

(230) to mount/dismount a designated data storage media cartridge on one of said media drive means

(211) , for determining whether said presently received request is directed to said stack loader means (221) ; and means (122) , responsive to said determining means (120, 121) , for ordering a sequence of said received requests for execution by said robot means (230) according to a predetermined priority.

12. The system of claim 11 wherein said ordering means (122) includes: means (901, 902) for determining whether unexecuted received requests directed to said media drive means (211) are pending for execution; means (903, 904), responsive to pending unexecuted received requests directed to said media drive means (211) , for queuing a presently received stack loader access request; and means (905) , responsive to said queuing means (903, 904) storing said presently received request, for immediately servicing one of said unexecuted requests directed to said media drive means (211) that has been pending the greatest length of time.

13. The system of claim 12 wherein said ordering means (122) further includes: means (903, 904, 906, 907) for servicing one of said unexecuted requests directed to said stack loader means (221) that has been pending the greatest length of time when there are no longer any unexecuted requests directed to said media drive means (211) .

14. The system of claim 13 wherein said ordering means (122) further includes: means (904, 907), responsive to said stack loader means (221) entering an idle state, for servicing said idle stack loader means (221) with a priority of said media drive means (211) .

15. The system of claim 14 further comprising: at least one access means (150) located in said array (202) for transferring data storage media cartridges into/out of said data storage media cartridge handling system.