Management of Magnetic Tapes

Identifiers:

	TSAR ID
	Manufacturer + Model Number + Serial Number

A tape store and retrieval unit (TSAR) is a housing about 10 feet long, 7 feet high, and 8 feet wide. Inside the TSAR are several thousand storage slots in which reels of magnetic tape can be placed. The TSAR is equipped with a robot which can be directed to travel about within the TSAR and to move magnetic tapes from one slot to another.

Arranged adjacent to the TSAR are several magnetic tape drives. These tape drives have been positioned in such a way that the robot can reach and manipulate them in order to mount and dismount tapes.

The slots used for storage of tape are located along the long (10 foot) walls of the TSAR housing.

1.1. TSAR.TSAR ID

Each TSAR has been assigned an identifier which is used by the operations and maintenance staff to distinguish between the TSARs in service at the computer center. The identifier is a single alphabetic character, painted conspicuously on the TSAR housing itself.

The TSAR identifiers are assigned by the Chief of Operations.

Domain: See above

1.2. TSAR.Manufacturer

This attribute records the name of the manufacturer of the TSAR.

Domain: manufacturer names

1.3. TSAR.Model Number

At the moment, there are several kinds of TSARs in service, which differ in minor ways. Some models have storage slots along both of the long walls of the housing; other models have only one long wall so equipped. In addition, the storage slots on some models are closer together, providing a closer packing and, therfore, a larger number of tapes can be placed in the same sized housing. Details on these and other minor differences between models of TSARs can be found in the manufacturer's technical and maintenance manuals.

The Model Number attribute records the manufacturer-stated model number for the TSAR.

Domain: model numbers (as stated by the manufacturers)

1.4. TSAR.Serial Number

Every TSAR housing is given a serial number at the time of manufacture. This attribute records that serial number, as bestowed by the manufacturer of the TSAR.

Domain: serial numbers, as given by the manufacturers

Identifiers:

	TSAR ID + Tape Location ID
	TSAR ID + Wall Number + Tier Number + Rank Number

Associated with each TSAR are a number of defined tape locations which can be reached by the tape robot. These locations fall into two types: (1) the tape storage slots (see object description for Tape Storage Slot) and (2) the magnetic tape drives accessible by the robot. The TSAR Tape Location object provides the formalization of both types of tape location within the TSARs.

Within a given TSAR, the tape locations are arranged along one or both of the long walls. Every tape location on a given wall is known by its "tier number", which is proportional to the vertical distance from the floor of the TSAR housing, and a "rank number", which is proportional to the horizontal distance from the left end of the wall as the robot faces it. The basic scheme for tape locations is shown in the following sketch.

Note that each of the magnetic tape drives has been assigned a tier number and a rank number, corresponding to the correct horizontal and vertical position for directing the robot.

TSARs, walls, tiers, and ranks form a natural identification scheme for TSAR tape locations. Note, however, that not all combinations of tier number and rank number correspond to a place where the robot can put a tape, since there are no tape storage slots in the area where the tape drives abut the TSAR housing.

2.1. TSAR Tape Location.TSAR ID (R)

Each tape location accessible by a tape robot is identified by the TSAR within which it lies plus a wall number, tier number, and rank number within the TSAR. This attribute provides the TSAR component of the identifier of the tape location.

Domain: Same as TSAR.TSAR ID

References:

Tape Robot.TSAR ID (across R3)

2.2. TSAR Tape Location.Wall Number

Each wall of the TSAR housing has been assigned a number (0 or 1) to identify it. This attribute tells on which wall the tape location has been placed.

Domain: wall numbers

2.3. TSAR Tape Location.Tier Number

The tape locations within the TSAR are arranged in horizontal rows, or tiers. Each tier of tape slots is assigned a tier number, which is proportional to the distance of the tier from the floor of the housing. Tiers are numbered from 0 at the bottom to 6 at the top of the wall.

Domain: tier numbers

2.4. TSAR Tape Location.Rank Number

Each tape location is assigned a rank number, which is proportional to the distance of the tape location from one end of the wall. Rank numbers start at zero at the left end of the wall (as seen by the robot), and continue to a maximum value at the right end.

Domain: rank numbers

2.5. TSAR Tape Location.Tape Location ID

This attribute provides an arbitrary identifier, created for the purposes of this model, for a tape location within a TSAR. The attribute was created to provide a concise way of modeling the subtype/supertype relationship that prevails between the TSAR Tape Location object and the Tape Storage Slots/Robot-Loaded Drive objects.

The domain of this attribute is arbitrary. Should such an identifier be required in implementation of an automated system, the domain could be defined as integers. Alternatively, a naming scheme based on the TSAR ID, wall number, tier number, and rank number could be devised.

Domain: See above

Identifiers:

TSAR ID + TSAR Tape Location ID

A Tape Storage Slot is TSAR Tape Location that is used for storage of magnetic tapes within the TSAR. The tape locations corresponding to the robot-loaded magnetic tape drives are not considered to be tape storage slots.

3.1. Tape Storage Slot.TSAR ID (R)

This attribute tells which TSAR contains the tape storage slot, and so formalizes the relationship Tape Storage Slot IS IN TSAR.

Domain: Same as TSAR.TSAR ID

References:

	TSAR.TSAR ID (across R2)
	TSAR Tape Location.TSAR ID (across R4)

3.2. Tape Storage Slot.TSAR Tape Location ID (R)

Each tape storage slot is regarded as being a tape location. This attribute provides the identifier of the tape location that corresponds to this tape storage slot, and so formalizes the relationship Tape Storage Slot IS A (SUBTYPE OF) TSAR Tape Location.

Domain: Same as TSAR Tape Location.Tape Location ID

References:

TSAR Tape Location.Tape Location ID (across R4)

3.3. Tape Storage Slot.Assigned Tape Reel ID (R)

Each tape reel selected for storage within a TSAR is assigned to a tape storage slot. This attribute tells which reel, if any, is assigned to this tape storage slot, and so formalizes the relationship TSAR Tape Reel IS ASSIGNED TO Tape Storage Slot.

Domain: Same as Tape Reel.Tape Reel ID

References:

TSAR Tape Reel.Tape Reel ID (across R7)

Identifiers:

	Drive Number
	TSAR ID + TSAR Tape Location ID

A Robot-Loaded Drive is a magnetic tape drive that has been specially constructed to allow loading of tapes on it by a tape robot. In every other regard, a Robot-Loaded Drive is an entirely standard tape drive.

4.1. Robot-Loaded Drive.Drive Number (R)

Every magnetic tape drive in the facility is assigned a unique drive number by the operations staff. This attribute provides the drive number for a robot-loaded tape drive.

See also the description of Drive.Drive Number.

This attribute is used to establish the relationship Robot-Loaded Drive IS A (SUBTYPE OF) Drive.

Domain: Same as Drive.Drive Number

References:

Drive.Drive Number (across R10)

4.2. Robot-Loaded Drive.TSAR ID (R)

Each robot-loaded drive is placed adjacent to a TSAR housing in such a way that the tape loading station of the drive lines up with a special loading slot on the TSAR housing. This attribute formalizes the relationship Robot-Loaded Drive IS ADJACENT TO TSAR.

Domain: Same as TSAR.TSAR ID

References:

	TSAR Tape Location.TSAR ID (across R4)
	TSAR.TSAR ID (across R5)

4.3. Robot-Loaded Drive.TSAR Tape Location ID (R)

Each robot-loaded drive can be viewed as a tape location within a TSAR, in that it provides a place to which the robot can deliver tapes. This situation is reflected in the model by the relationship Robot-Loaded Drive IS A (SUBTYPE OF) TSAR Tape Location.

This attribute, together with Robot-Loaded Drive.TSAR ID, formlizes the relationship Robot-Loaded Drive IS A TSAR Tape Location.

Domain: Same as TSAR Tape Location.Tape Location ID

References:

TSAR Tape Location.Tape Location ID (across R4)

Identifiers:

TSAR ID

A tape robot is a mechanical device that is capable of fetching a tape from a tape location in a TSAR, travelling to another point in the TSAR, and depositing the tape in a new tape location. The tape robot runs on tracks fixed to the floor of the TSAR housing.

The tape robot is a computer-controllable device.

5.1. Tape Robot.TSAR ID (R)

Each tape robot is housed in exactly one TSAR. This attribute tells the name of the TSAR in which the robot is housed, and so formalizes the relationship Tape Robot IS HOUSED IN TSAR.

Domain: Same as TSAR.TSAR ID

References:

TSAR.TSAR ID (across R1)

5.2. Tape Robot.Cycle State

The motions that the tape robot goes through are described as states in an operational cycle. Under normal circumstances, the robot progresses serially through states 1 to 6, as follows:

1. Idle. The robot is motionless and ready to accept a new "tape move" comand.
2. Accepting Command. The robot is accepting a "tape move" command. Each tape move command specifies a source wall, source tier, and source rank, as well as a target wall, target tier, and target rank. The meaning of the command is to move a tape from the source to the target location.
3. Seeking Source. The robot is moving to the source tape location.
4. At Source. The robot is positioned in front of the source tape location and is picking up the tape.
5. Seeking Target. The robot is moving to the target tape location.
6. At Target. The robot is positioned in front of the target tape location and is depositing the tape. Following this state, the robot will return to the Idle state.
   
   There are also several error states:
   
   
7. No Tape at Source. If the robot enters this state, the computer must issue a "robot reset" command to return the robot to the Idle state.
8. Dropped Tape. This state occurs if the robot ever picks up the source tape, but loses it before depositing it at the target tape location. If the robot enters this state, the operations staff must enter the TSAR housing and pick up the dropped tape; after which the computer must issue a "robot reset" command to return the robot to the Idle state.
9. Reset with Tape in Hand. This state occurs if a "robot reset" command is given when the robot is carrying a tape.

Domain: [ idle | accepting command | seeking source | at source | seeking target | at target | no tape at source | dropped tape | reset with tape in hand ]

5.3. Tape Robot.Current Wall Number

The wall currently being accessed by the tape robot. When the tape robot is in motion, the current wall number is considered to be the number of the last wall accessed.

Domain: wall numbers

5.4. Tape Robot.Desired Wall Number

The wall to which the tape robot is being directed. Under normal circumstances, the desired wall number will differ from the current wall number only when the tape robot is in motion. If, however, the robot is broken, it may stop before it reaches the new (desired) wall number.

Domain: wall numbers

5.5. Tape Robot.Current Tier Number

The tier currently being accessed by the robot. When the robot is in motion, the current tier number is undefined.

Domain: tier numbers or undefined

5.6. Tape Robot.Desired Tier Number

The tier to which the tape robot is being directed. Unless the robot is broken, the desired tier number will diff from the current tier number only when the tape robot is in motion.

Domain: tier numbers

5.7. Tape Robot.Current Rank Number

The rank currently being accessed by the robot. When the robot is in motion, the current rank number is undefined.

Domain: rank numbers or undefined

5.8. Tape Robot.Desired Rank Number

The rank to which the tape robot is being directed. Unless the robot is broken, the desired rank number will differ from the current rank number only when the tape robot is in motion.

Domain: rank numbers

5.9. Tape Robot.Computer Name (R)

Each tape robot is controlled by exactly one computer. This attribute provides the name of that computer, so formalizing the relationship Tape Robot IS CONTROLLED BY Computer.

Domain: Same as Computer.Computer Name

References:

Computer.Computer Name (across R6)

Identifiers:

Drive Number

A Drive is a computer-controlled magnetic tape drive which is used to read and write industry-standard magnetic tapes for programs running on the computer to which it is interfaced.

Each tape drive in the computer center is assigned one of two roles: It can be acting as an operator-loaded drive, in which case it can be interfaced to any of the general purpose computers, or it can be acting as a robot-loaded drive. In this case, the drive must be interfaced to a computer that is equipped with a TSAR.

6.1. Drive.Drive Number

Each tape drive has been assigned a drive number which is used by the operations and maintenance staff to distinguish between the drives in service at the computer center. The drive numbers are posted on the fronts of the drives.

Drive numbers are assigned from the integers by the maintenance group.

Domain: See above.

6.2. Drive.Number of Tracks

Each tape drive is equipped with magnetic heads which read and write bits in tracks longitudinally on the tape. The number of tracks that can be read or written is determined by the construction of the magnetic heads and supporting electronics.

Domain: number of tracks (7 or 9)

6.3. Drive.Density

Drives may read and write data in a variety of densities, measured in bits per (longitudinal) inch of tape. Standard densities available with the more modern drives are 800 bpi (bits per inch), 1600 bpi, and 6250 bpi. The computer center also maintains a few older drives to allow access to tapes which were originally written at 200 or 556 bpi.

Some drives allow a choice of density. Density selection, if available, is under computer control.

The Drive.Density attribute models the set of densities available on the drive.

Domain: [ 800 | 1600 | 6250 | 800 & 1600 & 6250 | 200 & 556 ]

Identifiers:

Drive Number

An Operator-Loaded Drive is a magnetic tape drive that is not associated with a TSAR and, therfore, must have magnetic tapes mounted on it by an operator.

7.1. Operator-Loaded Drive.Drive Number (R)

This attribute provides the drive number of the operator-loaded drive. It formalizes the relationship Operator-Loaded Drive IS A (SUBTYPE OF) Drive.

Domain: Same as Drive.Drive Number

References:

Drive.Drive Number (across R10)

7.2. Operator-Loaded Drive.Computer Name (R)

This attribute tells which computer the operator-loaded drive has been interfaced with. See the description of the relationship Drive IS CONTROLLED AND ACCESSED BY Computer.

Domain: Same as Computer.Computer Name

References:

Computer.Computer Name (across R11)

Identifiers:

	Computer Name
	Manufacturer + Model Number + Serial Number

The computer center operates a number of general-purpose computers for use by various departments of the company. Only general-purpose computers housed at the computer center and under the control of the operations staff are considered to be Computers in this model. Personal computers, network concentrartors, and various sepcial purpose machines do not qualify.

8.1. Computer.Computer Name

Every computer is assigned a name by the Operations Department. These names are in widespread use by operations, maintenance, and the computer users. The names are not posted on the machines, but appear on the Machine Schedule board in the user's lobby.

At one time the computers were named by a numbering system. Currently, however, they are named after Sesame Street characters: Big Bird, Oscar the Grouch, Cookie Monster, and the like.

Domain: See Above

8.2. Computer.Manufacturer

This attribute provides the name of the manufacturer of the computer.

Domain: computer manufacturers

8.3. Computer.Model Number

The model number of the computer, as stated by the manufacturer.

Domain: manufacturer model numbers

8.4. Computer.Serial Number

The serial number given to the central processor by the manufacturer.

Domain: manufacturer's serial numbers

8.5. Computer.Operating System

The name of the operating system used on this computer when in production.

Domain: operating system names

Identifiers:

Tape Reel ID

A Tape Reel is a magnetic tape which has been assigned a Tape Reel ID.

9.1. Tape Reel.Tape Reel ID

Each tape is assigned a unique identifier by the Operations staff before it is placed into service. The identifier is of the form yy-mm-v-n, where yy are the last two digits of the year, mm is a one or two digit month number, v is a single letter code identifying the company division to which the tape will be allocated, and n is a sequence number assigned sequentially through the month. The information encoded in the ID is purely for the convenience of the Operations staff, and is of no consequence to the usage of the tape.

Domain: See above

9.2. Tape Reel.Number of Tracks

The number of tracks written on the tape. This attribute is established at the time the tape is first written ("initialized", in the terminology of the computer center). See description of Drive.Number of Tracks.

Domain: Same as Drive.Number of Tracks

9.3. Tape Reel.Density

The density at which the tape was written. This attribute is established at the time the tape is initialized.

Domain: Same as Drive.Density

Identifiers:

Tape Reel ID

An operator-accessible tape reel is a reel of magnetic tape that is stored outside of the TSARs. Operator-accessible reels must be mounted on the operator accessible tape drives for use by programs.

10.1. Operator-Accessible Tape Reel.Tape Reel ID (R)

This attribute provides the identifier of a tape reel that has been classified as an operator accessible tape reel.

Domain: Same as Tape Reel.Tape Reel ID

References:

Tape Reel.Tape Reel ID (across R9)

Identifiers:

Tape Reel ID

A TSAR tape reel is a tape reel that has been placed in a TSAR.

11.1. TSAR Tape Reel.Tape Reel ID (R)

This attribute provides the identifier of a tape reel that has been classified as a TSAR tape reel.

Domain: Same as Tape Reel.Tape Reel ID

References:

Tape Reel.Tape Reel ID (across R9)

11.2. TSAR Tape Reel.TSAR ID (R)

At any time, a TSAR tape reel is to be found somewhere within the TSAR to which it has been assigned.

This attribute, together with TSAR Tape Reel.Current Tape Location ID, formalizes the relationship TSAR Tape Reel IS CURRENTLY LOCATED IN TSAR Tape Location.

Domain: Same as TSAR.TSAR ID

References:

TSAR Tape Location.TSAR ID (across R8)

11.3. TSAR Tape Reel.Current Tape Location ID (R)

This attribute tells which tape location within the TSAR currently holds the TSAR tape reel.

Domain: Same as TSAR Tape Location.Tape Location ID

References:

TSAR Tape Location.Tape Location ID (across R8)

Identifiers:

Mount ID

A tape mount is the mounting of a tape reel on a tape drive for the purposes of access by a program.

Tape mounts come in two types: Mounts done by an operator (formalized as Operator Tape Mounts) and Mounts done by a tape robot (formalized as TSAR Tape Mounts). This typing is reflected in the model by the subtype/supertype relationship between Tape Mount, Operator Tape Mount, and TSAR Tape Mount.

12.1. Tape Mount.Mount ID

An arbitrary identifier assigned to the Tape Mount for purposes of formalizing the subtype/supertype relationship Operator Tape Mount/TSAR Tape Mount IS A Tape Mount.

Domain: See above

12.2. Tape Mount.Date of Mount

Every tape mount occurs on a date. This attribute reflects the date on which the mount took place.

Domain: dates

12.3. Tape Mount.Time of Mount

Every tape mount occurs at a specific time of day. This attribute records the time at which the mount took place.

Domain: times

12.4. Tape Mount.Request ID (R)

Tape mounts are done at the request of a program that needs access to the tape. This attribute records the request that occasioned the mount. See also the description for the Tape Request object.

Domain: Same as Tape Request.Request ID

References:

Tape Request.Request ID (across R16)

Identifiers:

Mount ID

An Operator Tape Mount is the mounting of an operator-accessible tape reel on an operator-loaded drive.

Operator Tape Mount is an associative object used to formalize the (Mc:Mc) relationship Operator-Accessible Tape Reel HAS BEEN MOUNTED ON Operator-Loaded drive.

13.1. Operator Tape Mount.Tape Reel ID (R)

This attribute tells which tape reel participated in the mount.

Domain: Same as Tape Reel.Tape Reel ID

References:

Operator-Accessible Tape Reel.Tape Reel ID (across R12)

13.2. Operator Tape Mount.Drive Number (R)

This attribute tells which tape drive participated in the mount.

Domain: Same as Drive.Drive Number

References:

Operator-Loaded Drive.Drive Number (across R12)

13.3. Operator Tape Mount.Mount ID (R)

This attribute formalizes the relationship Operator Tape Mount IS A (SUBTYPE OF) Tape Mount.

Domain: Same as Tape Mount.Mount ID

References:

Tape Mount.Mount ID (across R14)

Identifiers:

Mount ID

A TSAR tape mount is the mounting of a TSAR tape reel on a robot-loaded drive.

TSAR Tape Mount is as associated object used to formalize the (Mc:Mc) relationship TSAR Tape Reel HAS BEEN MOUNTED ON Robot-Loaded Drive.

14.1. TSAR Tape Mount.Tape Reel ID (R)

This attribute tells which tape reel participated in the TSAR tape mount.

Domain: Same as Tape Reel.Tape Reel ID

References:

TSAR Tape Reel.Tape Reel ID (across R13)

14.2. TSAR Tape Mount.Drive Number (R)

This attribute tells which tape drive participated in the mount.

Domain: Same as Drive.Drive Number

References:

Robot-Loaded Drive.Drive Number (across R13)

14.3. TSAR Tape Mount.Mount ID (R)

This attribute formalizes the relationship TSAR Tape Mount IS A (SUBTYPE OF) Tape Mount.

Domain: Same as Tape Mount.Mount ID

References:

Tape Mount.Mount ID (across R14)

Identifiers:

	Request ID
	Computer Name + Tape Reel ID + Date + Time

Whenever a program requires a tape (other than a scratch tape), it issues a tape request. Each tape request specifies the particular type required, the computer and program to which the tape is to be made available, and the time and date of the request.

Each tape request is eventually satisfied by a tape mount.

Tape Request is an associative object used to formalize the relationship Tape Reel WAS REQUESTED FOR USE BY PROGRAM RUNNING ON Computer (Mc:Mc).

15.1. Tape Request.Request ID

Each tape request within a particular computer is assigned a request ID—a number— by the operating system. This attribute records that request ID.

Domain: See above

15.2. Tape Request.Computer Name (R)

Each tape request originates in a single computer. This attribute records the computer in which the request was generated.

Domain: Same as Computer.Computer Name

References:

Computer.Computer Name (across R15)

15.3. Tape Request.Tape Reel ID (R)

This attribute tells which tape reel was being asked for in this tape request.

Domain: Same as Tape Reel.Tape Reel ID

References:

Tape Reel.Tape Reel ID (across R15)

15.4. Tape Request.Date

This attribute records the date of the tape request.

Domain: dates

15.5. Tape Request.Time

This attribute records the time of the tape request. It is assumed that time is recorded to such precision that a single tape reel cannot be requested twice at the same Tape Request.Time by programs running in the same computer.

Domain: times

15.6. Tape Request.Program Requesting

Every tape request is generated by a program. This attribute records the name of the program that generated the tape request.

Domain: program names