You can obtain information
on all magnetic tape device characteristics by using the Get Device/Volume
Information ($GETDVI) system service. (See the HP OpenVMS System Services Reference Manual.)
See the Help files for more information on the $GETDVI system
service.
$GETDVI returns magnetic tape characteristics
when you specify the item codes DVI$_DEVCHAR, DVI$_DEVCHAR2, DVI$_DEVDEPEND,
and DVI$_DEVDEPEND2. Tables Table 3-1, Table 3-2, and Table 3-4 list
these characteristics. The $DEVDEF macro defines the device-independent
characteristics, the $MTDEF macro defines the device-dependent characteristics,
and the $MT2DEF macro defines the extended device characteristics.
The extended device characteristics apply only to the TU81-Plus tape
drive.
Table 3-1 Magnetic Tape Device-Independent Characteristics
Characteristic[1] | Meaning |
|---|
| | Dynamic Bits (Conditionally Set) |
DEV$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$M_WBC[2] | Device is capable
of write-back caching. |
Table 3-2 Device-Dependent Information for Tape Devices
Characteristic[1] | Meaning | |
|---|
MT$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$K_BLK_833 | Cartridge block mode recording[2] |
MT$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 3-3 Device-Dependent Information for Tape Devices
Characteristic[1] | 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.
