Magnetic Tape Driver Device Information

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HP OpenVMS I/O User's Reference Manual

Magnetic Tape Drivers

Driver Features

Magnetic Tape Function Codes

Magnetic Tape Driver Device Information

You can obtain information on all magnetic tape device characteristics by using the Get Device/Volume Information ($GETDVI) system service. (Refer to the HP OpenVMS System Services Reference Manual.)

$GETDVI returns magnetic tape characteristics when you specify the item codes DVI$_DEVCHAR, DVI$_DEVCHAR2, DVI$_DEVDEPEND, and DVI$_DEVDEPEND2. Magnetic Tape Device-Independent Characteristics, Device-Dependent Information for Tape Devices, and Extended Device Characteristics for Tape Devices list these characteristics. The $DEVDEF macro defines the device-independent characteristics, the $MTDEF macro defines the device-dependent characteristics, and the $MT2DEF macro defines the extended device characteristics. The extended device characteristics apply only to the TU81-Plus tape drive.

Table 1 Magnetic Tape Device-Independent Characteristics
Characteristic¹ Meaning

Dynamic Bits (Conditionally Set)

DEV$M_AVL
Device is on line and available.

DEV$M_FOR
Volume is foreign.

DEV$M_MNT
Volume is mounted.

DEV$M_RCK
Perform data check on all read operations.

DEV$M_WCK
Perform data check on all write operations.

Static Bits (Always Set)

DEV$M_FOD
Device is file-oriented.

DEV$M_IDV
Device is capable of input.

DEV$M_ODV
Device is capable of output.

DEV$M_SQD
Device is capable of sequential access.

DEV$M_WBC²
Device is capable of write-back caching.

**Table 1** **Magnetic Tape Device-Independent Characteristics**
Characteristic¹	Meaning
	Dynamic Bits (Conditionally Set)
DEV$M_AVL	Device is on line and available.
DEV$M_FOR	Volume is foreign.
DEV$M_MNT	Volume is mounted.
DEV$M_RCK	Perform data check on all read operations.
DEV$M_WCK	Perform data check on all write operations.
	Static Bits (Always Set)
DEV$M_FOD	Device is file-oriented.
DEV$M_IDV	Device is capable of input.
DEV$M_ODV	Device is capable of output.
DEV$M_SQD	Device is capable of sequential access.
DEV$M_WBC²	Device is capable of write-back caching.

Table 2 Device-Dependent Information for Tape Devices
Characteristic³ Meaning

MT$M_LOST
If set, the current tape position is unknown.

MT$M_HWL
If set, the selected drive is hardware write-locked.

MT$M_EOT
If set, an end-of-tape (EOT) condition was encountered by the last operation to move the tape in the forward direction.

MT$M_EOF
If set, a tape mark was encountered by the last operation to move the tape.

MT$M_BOT
If set, a beginning-of-tape (BOT) marker was encountered by the last operation to move the tape in the reverse direction.

MT$M_PARITY
If set, all data transfers are performed with even parity. If clear (normal case), all data transfers are performed with odd parity. Only nonreturn-to-zero-inverted recording at 800 bits/inch can have even parity.

MT$V_DENSITY MT$S_DENSITY
Specifies the density at which all data transfer operations are performed. Possible density values are as follows:

MT$K_GCR_6250
Group-coded recording, 6250 bits/inch

MT$K_PE_1600
Phase-encoded recording, 1600 bits/inch

MT$K_NRZI_800
Nonreturn-to-zero-inverted recording, 800 bits/inch

MT$K_BLK_833
Cartridge block mode recording⁴

MT$V_FORMAT MT$S_FORMAT
Specifies the format in which all data transfers are performed. A possible format value is as follows:

MT$K_NORMAL11
Normal PDP-11 format. Data bytes are recorded sequentially on tape with each byte occupying exactly one frame.

MT$_FASTSKIP_USED
If set, the most recent IO$_SKIPFILE function was performed using the optimized SCSI space-by-file-marks algorithm. (See Skip File for more information about the IO$M_ALLOWFAST modifier to the IO$_SKIPFILE function.)

**Table 2** **Device-Dependent Information for Tape Devices**
Characteristic³	Meaning
MT$M_LOST	If set, the current tape position is unknown.
MT$M_HWL	If set, the selected drive is hardware write-locked.
MT$M_EOT	If set, an end-of-tape (EOT) condition was encountered by the last operation to move the tape in the forward direction.
MT$M_EOF	If set, a tape mark was encountered by the last operation to move the tape.
MT$M_BOT	If set, a beginning-of-tape (BOT) marker was encountered by the last operation to move the tape in the reverse direction.
MT$M_PARITY	If set, all data transfers are performed with even parity. If clear (normal case), all data transfers are performed with odd parity. Only nonreturn-to-zero-inverted recording at 800 bits/inch can have even parity.
MT$V_DENSITY MT$S_DENSITY	Specifies the density at which all data transfer operations are performed. Possible density values are as follows:
	MT$K_GCR_6250	Group-coded recording, 6250 bits/inch
	MT$K_PE_1600	Phase-encoded recording, 1600 bits/inch
	MT$K_NRZI_800	Nonreturn-to-zero-inverted recording, 800 bits/inch
	MT$K_BLK_833	Cartridge block mode recording⁴
MT$V_FORMAT MT$S_FORMAT	Specifies the format in which all data transfers are performed. A possible format value is as follows:
	MT$K_NORMAL11	Normal PDP-11 format. Data bytes are recorded sequentially on tape with each byte occupying exactly one frame.
MT$_FASTSKIP_USED	If set, the most recent IO$_SKIPFILE function was performed using the optimized SCSI space-by-file-marks algorithm. (See Skip File for more information about the IO$M_ALLOWFAST modifier to the IO$_SKIPFILE function.)

Table 3 Extended Device Characteristics for Tape Devices
Characteristic⁵ Meaning

MT2$V_WBC_ENABLE
If set, write-back caching is enabled for this unit.

MT2$V_RDC_DISABLE
If set, read caching is disabled for this unit.

**Table 3** **Extended Device Characteristics for Tape Devices**
Characteristic⁵	Meaning
MT2$V_WBC_ENABLE	If set, write-back caching is enabled for this unit.
MT2$V_RDC_DISABLE	If set, read caching is disabled for this unit.

DVI$_DEVTYPE and DVI$_DEVCLASS return the device type and class names, which are defined by the $DCDEF macro. DVI$_DEVBUFSIZ returns the buffer size. The buffer size is the default to be used for tape transfers (normally 2048 bytes). The device class for magnetic tapes is $DCTAPE, and the device type is determined by the magnetic tape model. For example, the device type for the TA78 is DT$_TA78; for the TA81 it is DT$_TA81.

This function code takes no function-dependent arguments.

Footnotes

1 Defined by the $DEVDEF macro.

2 This bit is located in DVI$_DEVCHAR2.

3 Defined by the $MTDEF macro.

4 Only for the TK50 and TZ30 tape drives.

5 Defined by the $MT2DEF macro. Only for the TU81-Plus. Initial device status will show both of these bits cleared; write-back caching will be disabled, read caching will be enabled.

( Number takes you back )

Driver Features

Magnetic Tape Function Codes