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Device Names

TOPS-10 supports a number of peripheral input/output devices to handle
data acquisition, storage, retrieval, and display.  These devices are:

     Card Punch            Card Reader          DECtape
     Disk                  Display Terminal     Graphics Display
     Hard-copy Terminal    Line Printer         Magnetic Tape
     Paper Tape Punch      Paper Tape Reader    Plotter

The monitor allocates a device to your job when you request access  to
the  device.  (See the ASSIGN and MOUNT commands.) Until you request a
device, it resides in the system pool of available resources.

To reference a device, you must specify a device name.  The  types  of
device   names   are:    generic,   physical,   logical,  ersatz,  and
system-defined logical.

Generic Device Names

The most general type of device name is the generic device name.  When
you  specify  a  generic  name, the monitor selects a free unit of the
device  type  specified.   When  your  computer  is   in   a   network
environment, the monitor chooses the device from those devices at your
location, or, if none are available, the monitor  chooses  the  device
from the host (central) site.

A generic name can be two or three letters long and is followed  by  a
colon  (:).   Two-character  generic  names  are  less  specific  than
three-character generic names.  For example, MT:  means  any  magnetic
tape  unit,  but  MTA:  means  any magnetic tape unit on controller A.
When you specify the generic name DSK: or DS:, the monitor  uses  your
job  search list to determine which disk device should be selected for
you.  For help on search lists, see the help file SERLST.

Generic Device Names

                                       3-Letter          2-Letter
  Device                             Device Name       Device Name

  Card punch                             CDP:              CP:
  Card reader                            CDR:              CR:
  Console terminal                       CTY:              ---
  DECtape                                DTx:              DT:
  Disk                                   DSK:              DS:
     Packs                               DPx:              DP:
                                         RPx:              RP:
     Fixed head                          FHx:              FH:
                                         FSx:              FS:
  Display                                DIS:              ---
  Line printer                           LPT:              LP:
     lowercase/uppercase                 ---               LL:
     uppercase                           ---               LU:
  Magnetic tape                          MTx:              ---
     7-track                             ---               M7:
     9-track                             ---               M9:
  Operator terminal                      OPR:              ---
  Paper-tape punch                       PTP:              PP:
  Paper-tape reader                      PTR:              PR:
  Plotter                                PLT:              ---
  Pseudo-terminal                        PTY:              ---
  System library                         SYS:              SY:
  Terminal                               TTY:              TT:

When  you  specify  a  generic   name,   the   monitor   selects   the
lowest-numbered  available  unit  of the device type specified.  There
are two defaults when you specify a generic name:

     1.  When your program specifies DSK or DS, the system  uses  your
         job search list.

     2.  When you specify TTY: or TT:, the monitor always selects your
         terminal (assuming that these are not logical names).

Physical Device Names

Every I/O device has a physical  name.   This  name  consists  of  the
generic  name,  a  letter  indicating  the controller, and one numeric
character indicating the unit number.  For example, the  generic  name
MTA: indicates any magnetic tape unit on controller A.  However, MTA1:
indicates magnetic tape unit 1 on controller A.

File Structures

The  TOPS-10  operating  system  organizes  disk  devices  into   file
structures.   File  structures  are  logical  arrangements of 128-word
blocks on one or more disk units.  A file structure can exist  on  one
disk unit, or it can be distributed over several disk units designated
by a single name.  However, two file structures cannot  exist  on  the
same unit.

The operator or system administrator assigns  a  name  to  every  file
structure  when  he or she defines the system's file structures.  This
name is one to four characters long, and cannot duplicate  a  physical
device  name,  a  unit  name, or an existing file structure name.  The
recommended   names   for   public   file   structures   are    DSKA:,
DSKB:,...,DSKO: in order of decreasing speed.

File structures are illustrated and explained in detail in the TOPS-10
Monitor Calls Manual, Vol.  1.

Logical Device Names

You can assign a logical name to a physical device.  The monitor  will
recognize  the  name  that  you assign, and associate the logical name
with the physical device.  You can assign a logical name to  a  device
using the ASSIGN command.

The logical name that  you  assign  may  be  up  to  six  alphanumeric
characters  and  may  optionally be ended by a colon (:).  Thereafter,
the monitor will use the device that you associated with  the  logical
name,  when  you  or your programs specify that logical name.  Logical
names are cleared by the DEASSIGN command.  That is, use the  DEASSIGN
command to disassociate logical names from devices.  Logical names are
also cleared when you log off the system, and when you specify another
logical name for the same device.

Logical names are useful when you are writing a program that  needs  a
device,  but you will not know until program execution what device you
will need.  Use a logical name in the program to represent the device.
Before  you  run  the  program use the ASSIGN command to associate the
logical name with a physical device.

Logical names take precedence over physical names.  Therefore, if  you
assign the logical name DSK: to the device MTA3: (magnetic tape unit 3
on controller A), all output to generic DSK will go  to  the  magnetic

Some names are recognized by the  monitor  as  special  system-defined
logical  names that the monitor translates into physical device names.
One example is the generic device name OPR:.  The generic name OPR: is
the system-default logical name for the operator's terminal.

Therefore, the terminal specified as OPR:  can  change  during  system
operation;  but  if  you  send  a message to OPR:, the message will be
routed to the last physical  device  declared  to  be  the  operator's
terminal at your node.

All devices except terminals can be  designated  as  being  restricted
devices.   You  request  a  restricted  device from the system pool of
available resources  by  issuing  the  MOUNT  command.   This  command
requires operator intervention before the specified device is assigned
to your job.  The system deassigns a restricted device from  your  job
when you log off the system or issue the DISMOUNT, DEASSIGN, or FINISH

Unrestricted devices  are  assigned  to  your  job  on  a  first-come,
first-served  basis  when  you issue the MOUNT or ASSIGN command.  The
device assignment remains in effect until you release  the  device  by
issuing  a  DEASSIGN  command  or a FINISH command, or you log off the

The following example illustrates the use of both physical and logical
device names.


     You request a DECtape drive with the logical name ABC:


     The monitor gives you unrestricted device DTA0: (DECtape number 0
     on controller A).  You then mount a DECtape on drive DTA0:


     You request any paper-tape punch and  request  that  the  logical
     name ABC: be assigned to it.


     The monitor prints  a  warning  message,  telling  you  that  the
     logical  name  was  previously  assigned  to another device.  The
     monitor changes the logical-name assignment, so that the  logical
     name ABC: now refers to the paper-tape punch.


     You run the system program PIP.

     .R PIP

     You issue a command string to PIP asking that file  FILEA.EXT  be
     transferred  from  device  DTA0: to logical device ABC: (physical
     device PTP0:).


     You type a CTRL/C, returning your job to monitor mode.


     You request another DECtape drive and request that  logical  name
     DEF: be assigned to it.


     The monitor prints a message telling you that all DECtape  drives
     are  in use by the specified jobs.  The monitor does not assign a
     DECtape drive or a logical name to your job.


     You request that DECtape unit 0 (which you already have  assigned
     to you) be assigned the logical name DEF:.


     DECtape unit 0 takes on the logical name DEF:.


     You deassign the paper-tape  punch,  clearing  the  logical  name


     You run the system program PIP.

     .R PIP

     You request that the file FILEB is to be transferred from  device
     DEF: to device ABC:


     TOPS-10 prints an  error  message  indicating  that  the  logical
     device name ABC: is no longer assigned.


     You type a CTRL/C, returning your job to monitor mode.


     You request drive DTA0: (DECtape drive 0) again and request  that
     the logical DEF: be changed to XYZ:


     The system  disassociates  the  logical  name  DEF:  from  DTA0:.
     DECtape unit 0 takes on the logical name XYZ:.


Ersatz Device Names

An ersatz device is a disk-simulated library.  Although you specify an
ersatz  device  like  a  file structure, an ersatz device represents a
particular project-programmer number  on  a  disk  structure.   Ersatz
device  names are three characters long.  See the help file ERSNAM for
a complete list of the ersatz device names used by TOPS-10.