This paper describes how to use the PDP15 under the Disc Operating System (DOS). The document includes (in section 1) the normal procedure for starting to use the PDP15 and for finishing; all users are expected to follow this. The 'starting DOS' procedure in 1.1 may look lengthy, but in practice it normally works out as a series of quick checks.
The remainder of the document is oriented towards the user of programs rather than the program developer; basically, it will tell such a user as much about DOS as is necessary in order to run a program with some knowledge of what options are available and what the loading instructions mean.
Section 2 on DOS commands could usefully be studied by someone learning how to use DOS and there are several examples which can be worked through on the computer. Loading instructions for particular programs are described ia other documents (see Appendix 5) for references, section 4 gives a brief outline of some programs available. These loading instructions include DOS commands and so an understanding of the commands in section 2.1 and 2.2 will help towards an understanding of what the loading instructions are doing.
Section 3 describes DOS error messages (as distinct from errors that are detected by a user program).
This document supersedes the description of DOS in the paper about VIEW (section 2 of SPROGS Technical Paper 9).
CONTENTS:-
1. PROCEDURE FOR STARTING AND FINISHING USING THE PDP15
1.1 Starting DOS
1.2 Starting a binary paper tape program other than the DOS bootstrap
1.3 Finishing
2 DOS COMMANDS
2.1 Commands immediately executed by DOS
(ASSIGN: BUFFS: DATE: INSTRUCT: KEEP: LOG: LOGOUT: REQUEST: TIME: VT)
2.2 DOS commands to load programs
(System programs: EXECUTE or E: DDT, DDTNS, GLOAD,LOAD: GET,GETP, GETS, GETT)
3 ERRORS IN USING DOS
3.1 IOPS messages
3.2 Loading errors .LOAD and .SYSLD
3.3 Others
4 USEFUL PROGRAMS
4.1 MTDUMP
4.2 CAMP/CAMPER
4.3 FONTS
4.4 LISTIT
4.5 VIEW
Appendix 1 Typing conventions used by DOS
Appendix 2 Loading paper tapes, ½" tapes and DEC tapes
Appendix 3 Layout of the PDP15 console
Appendix 4 PDP15 peripherals and abbreviations
Appendix 5 References
When starting to use the PDP15 and intending to use DOS, the following procedure must always be used, whether or not DOS is already started.
Fill in names and starting time in the log book; this is contrary to the previous practice on the PDP15, where logging-in took place only at switch-on. (The log is in the white folder, usually open on top of the PDP15 bookcase. The log should also be used for recording finishing time and noting faulty behaviour of the system). Normally also, time should be booked in the PDP15 diary, in order to ensure that time is available when needed. External users cannot book time during the day, however, although they can use the PDP15 during the day if no internal user requires it.
Glance at the white board on the wall because on this will be written any current or temporary important information about the state of the PDP15 (for example "The display will be unusable until.... ")
The disc is powered separately from the computer. The 2 green pilot lamps on the 2 disc cabinets and the lights of the disc processor (on the front of one of the disc cabinets) should be on. Check that they are on. If the disc appears to be off, inform one of the operators and do not attempt to use the system.
Check that the computer is switched on, it is normally left on all day and night and the console lights (just above the small working surface and the switches) will be on if it is.
If the computer is off, switch on at the console (diagram in Appendix 3). Note that in this case the computer will have to be started from 77646 (ie step (e) will fail but step (f) will work).
At this stage, the computer should be on. Check that the central teletype (or "system teletype", normally the KSR35) is also on, it possesses its own switch.
Type 'ctrlC' on the system teletype (Appendix 1 explains 'ctr1C'). The teletype should type:-
↑C (echo for 'ctr1c')
DOS-15 Vnn
$
At this point you are in DOS and can start typing DOS commands. This will normally work if DOS or a program called by DOS is working.
There is a 'keyboard listener'' which enters the core-resident DOS bootstrap when 'ctrlC' is typed. The bootstrap then reads in from disc a decoder for DOS commands and a loader for system programs. The computer then types $ as a signal of its readiness to receive a DOS command. For the first DOS command of the session consider step (1). You can then use any of the commands in section 2.
If 'ctrlC' does not work, it is necessary to restart the computer directly from an address in the bootstrap, using the console switches (see Appendix 3 for diagram).
(1) Set address switches to 77646 (octal).
(2) Press 'STOP' and 'RESET'.
(3) Press 'START' and DOS should start as follows:-
DOS-15 Vnn ENTER DATE (mm/dd/yy) - 2/28/73 (type date in form month/date/year or in form mmddyy eg 022873) $
At this point DOS is ready. User's response is emphasised. Note the American date.
If restarting does not work, the bootstrap is probably corrupted and must be reloaded from paper tape (DOS BOOTSTRAP), again using the console switches.
(1) Load paper tape in reader (see Appendix 2 for instructions), remembering to press the button for the reader.
(2) Set address switches to 77637.
(3) Press 'STOP' and 'RESET'.
(4) Press 'READIN'.
(5) DOS should start as in (f).
In this case, there is something wrong with the system. Inform one of the operators. In any case, record the occurrence in the log book. Do not attempt any thing further yourself, as such an action may corrupt a part of the system which is functioning perfectly well. For instance, do not attempt to recreate the DOS system on the disc. The only binary paper tape program an external user or a casual internal user should use is the DOS bootstrap.
In this case then it is advisable for you to type LOGOUT in case the previous person has not done so. This will clear any settings made by the previous user, in particular his device assignments (section 2 1.7 )
↑C DOS-15 Vnn $ LOGOUT $
Operators or certain internal users may have reason to load a paper tape program, for instance DOSSAV, the program to save or restore the disc. Steps 1.1 (a)-(d) will be necessary. Then, instead of typing 'ctr1C' at step (e), read in the paper tape required. The address to set up or the address switches is not normally the same as the DOS bootstrap, but is written on the tape itself.
Note that some programs are not self starting (in contrast to DOSSAV and the DOS bootstrap).
This is using the paper tape reader in hardware-read-in mode.
(a) Switch off the ½" tape decks if necessary. These are powered separately from the computer.
(b) Make sure that the VT screen is cleared. This means that any program making use of the display (eg VIEW) must be terminated (normally with 'ctrlC'). If in DOS and if there is text on the screen, type VT OFF.
This is important, since going away and leaving an image on the screen will unnecessarily shorten the tube life.
(c) Switch the system teletype off; this too has its own switch.
(d) Leave the computer on. The computer is now normally left switched on through the day and night.
(e) Make an entry in the PDP15 log book. This should record finishing time and should record any system errors or unusual occurrences.
After typing 'ctr1C', or starting DOS from the switches (section 1.1), the '$' sign is a signal that a DOS command can be typed on the system teletype.
While typing a command (or any input to a program from the system teletype), remember that characters and a whole line can be erased and retyped if necessary; this can be done provided that the line terminator has been typed. The line terminator is 'carriage return' or 'altmode' and must be typed before the whole line is accepted by the system. Appendix 1 describes these typing conventions.
A user of DOS works in 2 phases.
(a) The user can work directly under the control of DOS and specify the conditions under which a program is to run. Section 2.1 describes these commands. DOS types $ each time the user is to type a command.
(b) The user can load the program, which then initiates all I/O to the system teletype. In other words, no DOS commands can be typed. When the program terminates itself (eg by executing a FORTRAN STOP) or the user terminates it by typing 'ctrlC', DOS regains control. The user can now type DOS commands again.
A full description of DOS commands is found in the PDP15 DOS Users' Manual (reference 2). The pocket book 'PDP15/20 User's Guide" (reference 1) is also useful, but in fact describes an older system than DOS; however, it does include most of the DOS commands.
The intention of this section (section 2) is to enable a person, who is not programming the PDP15, to run other people's programs. Therefore it should not normally be necessary to refer to the full DOS Users' Manual.
DOS permanently contains a table ("Device Assignment Table" or "DAT") with numbered slots from -15 to (normally) 20 octal. Each numbered slot contains a reference to a device handler program. A program makes an I/0 request to a numbered slot. (For instance; a program wishes to WRITE to slot 6. Suppose that slot 6 refers to a paper tape punch handler PPA). DOS converts the WRITE to an I/0 request to a device handler (In this example DOS requests PPA to WRITE a record. PPA controls all output to the paper tape punch). The 'A' in 'PPA' is a version letter; other paper tape punch handlers can be 'PPB', 'PFC' etc. The purpose of more than one handler per device is to allow smaller and simpler handlers as alternatives to the comprehensive ones. 'PP' is equivalent to 'PPA' and normally the 'A' version is the largest and most comprehensive. The table can be listed on the teletype by the REQUEST command (2.1.8).
Slot assignments can be changed with the ASSIGN command (A or ASSIGN) (remember 'carriage return' or 'altmode').
Some examples:-
$ASSIGN PPA 6 (Assign paper tape punch PPA to slot 6.)
$A PP 6 (Same effect.)
$A TT 3,4 (Assign system teletype to more than one slot)
$$A PRC 3 (Assign 'C' version of paper tape reader handler.)
$A MT1 7 (Magnetic tape requires unit number (as dialled on transport).
DECtape also requires unit number)
$A VW 4/TT 5,6 ('/' divides >1 assignment)
$A DK <JRG> 7 (Each user area, indicated by <>, on the disc is treated
by the software as a separate device)
$A <JRG> 7 (Changes the disc area to <JRG>. Doesn't have any meaning unless
some disc area is already assigned to 7 )
A DT1 -4 (A loader 1ike LOAD, GLOAD reads in a program from a negative slot)
At any time, the set of assignments can be checked by using the REQUEST command (see 2.1.8) to type them out.
Assignment changes only remain in force for one program entry and exit; 'ctrlC' restores the standard set. The standard set can be listed by:-
↑C (Echo from 'ctrlC' or could use LOGOUT
$KEEP OFF
$R
list of slots and assignments
$
$LOGOUT
$VT OFF (Useful to clear the screen)
$A <SYS> -4 (Assigns DK <SYS> to -4. This assumes that DK is already assigned)
$E VIEW (This command loads VIEW program)
..... VIEW commands
↑C (echo from 'ctrlC')
DOS-15 Vnn
$A <SYS> - 4 (Need to redo assignment because of 'ctrlC')
$A DT2 6 (Slot 6 is used by the program LISTIT to input a fi1e.
Assign it to DECtape unit 2)
$E LISTIT
..... LISTIT Commands
↑C
DOS-15 Vnn
$A DK <FRA >-4 (FONTS program exists on FRA user area)
$A TT 4 (Now assign positive slots for FONTS data)
$A DT1 2
$A LTI 6 (Assign display keyboard to slot 6)
$A VT 10
$E FONTS
... etc
A command for pre-allocating core space for disc buffers. How you use this will depend on the program you're using; VIEW doesn't need it; CAMP and CAMPER require it but this is documented in the CAMP and CAMPER manual. Basically a program requires one buffer for each disc file it has open at one time.
The date is normally typed in when the system is started up (1.I f) it is possible to get DOS to type out the date and it is possible to change it.
To get DOS to type the date:-
$ DATE (or $D)
DATE 02/28/73
$
To change the date, use DATE mm/dd/yy or
DATE mmddyy, where mm=month (01-12), dd=day (01-31), yy=year (70-99);
for example
$DATE 2/28/73
$DATE 022873
$D 2/26/73
INSTRUCT types out a list of DOS commands.
INSTRUCT ERRORS types a list of DOS errors.
Both print outs are long and can be terminated with 'ctrlP'.
2.1.1 said that 'ctrlC' restores the standard set of DAT slot assignments. The commands KEEP ON causes an altered table to be the new standard. This saves slot assignments from one run to the next. For example:-
$LOGOUT $A <SYS> -4 $KEEP ON $E VIEW ..... VIEW Commands ↑C $E VIEW (A <SYS> -4 is unnecessary since KEEP ON was typed) .... VIEW Commands ↑C $KEEP OFF $A <SYS> -4 (Assignment is again necessary) $E VIEW KEEP OFF restores the default standard
An occasionally useful comment facility
$LOG THIS LINE IS TERMINATED WITH CARRIAGE RETURN (AS IS THIS) AND SO 'LOG' KEEPS CONTROL, 5 SPACES ARE PUT OUT BY 'LOG' THIS LINE ENDS WITH ALTMODE 1- WHICH MEANS END OF COMMENT ' $
There is a LOGIN command but people not programming the PDP15 will not need it. It is useful to type LOGOUT as you start using the machine (However perverse this may seem). This has the effect of clearing the previous user's standard assignments if he has altered them (it includes the effect of KEEP OFF (2.1.5) ). For instance:-
$LOGOUT $VT OFF $A <SYS> - 4 $E VIEW etc
The ASSIGN section (2.1. 1) describes the assignment table. REQUEST or R types the currently active table, for example:-
$A <SYS> -4
$MT2 6
$REQUEST (or $R)
DAT DEVICE UIC
-15 DKA ZZ
.
.
.
-4 DKA SYS
.
6 MTA2 ZZZ
.
.
.
20
$
REQUEST can be used at any time (after a DOS $) to check assignments.
It is possible to cut down the printing by- typing "R (or REQUEST) name" where name can be the letters USER or any of the system program names in section 2.2. For example:-
$R USER (Just prints the positive slots)
. DAT.........
1
.
.
.
20
$
The printout can be put on the display for speed using VT ON and 'ctrlX' (2.1.10).
Like DATE (2.1.3), it is possible to get DOS to type out the time and it is possible to set it. The time has no special significance for any of our existing programs but it may be useful as a record in a console session.
To set the time, use "TIMEhhmm" where hh=hours (00-23) and mm=minutes (00-59) for example:-
$TIME 0830 (or $T 0830) $TIME 2355 to get DOS to type the time:- $TIME (or $T) TIME 083256 $
It is possible to command DOS to send to the display all messages intended for the system teletype. The DOS commands are" VT ON" and "VT OFF".
When VT is OFF (most recent VT command is VT OFF), no listing on display is possible.
When VT is ON, listing can be switched between display and teletype at any time by typing 'ctrlX'. 'ctrlX' can be typed while a program is running. Warning: it is inadvisable to use 'ctrlX' to switch, if a graphics program is running (for instance it should not be used while VIEW is running).
When 'ctrlX' has switched output to the display, pushbutton 5 off (counting from left) makes the output 'scroll' when the bottom of the screen is reached; button 5 on is 'page mode' and, at the bottom of a page, button 6 has to be pressed to get a new page. You will observe that button 5 can hold up the whole machine. For example:-
$yT ON $;ctrlX followed by REQUEST listing on display; can find out existing assignments quickly A <SYS> - 4 (No $ on teletype, since it appears on display) #E LISTIT etc (LISTIT dialogue will appear on the screen)
There are a variety of ways in which a program can be loaded from DOS; which way is correct for a particular program depends on how the binary has been stored.
All system programs are loaded by just typing the name (and 'return'). Anyone not programming under DOS will only be interested in MTDUMP, the ½" tape list and copy program (this is outlined in section 4.1). Programmers will use CHAIN for building overlays, DTCOPY, DUMP for printing a core dump, EDIT for editing character files, EDITVT for doing the same using the VTI5, F4 compiling FORTRAN programs, MACRO for compiling assembly language (MACRO-15) programs, PIP for transferring files (binary or character) from one device to another, UPDATE for building libraries and collective binary fields (SPROGS 9). For example:-
$A TT 3 $MTDUP MTDUMP message <now type MTDUMP commands
Most Atlas written programs (see section 4) are made available this way; this loadable form is produced by the CHAIN system program and consists of 2 files ZZZZZZ XCU and ZZZZZ XCT where ZZZZZZ is the program name.
$A <SYS> -4 (EXECUTE reads in the program via slot -4)
$A DT1 3 (A positive slot used by the program)
$E LISTIT
The EXECUTE program in this example would look for file LISTIT XCU and LISTIT XCT on disk area <SYS>
The "linking loader" loads one or more files each of which contains relocatable binary (which is output by the assembler and FORTRAN compiler).
There are 4 possible commands for using the linking loader. DDT is used when the programmer wishes to examine locations in the program and insert breakpoints. DDTNS saves space by preventing the use of local symbols. GLOAD loads the program and starts it without intervention from the user. LOAD just loads it and waits for a command from the user to start it (ctrlS) or dump it (ctrlQ).
A description can be found in the User's Guide
Example
$A DK <ALF> -5 (Loader looks for a file .LIBR5 BIN via slot
-5 and uses it as a library. If -5 assigned
to NON, loader does not look for .LIBR5 BIN)
$A DT1 -4 (Loader reads binary via slot -4. Assign it to
DEC tape unit 1)
$LOAD
LOADER Vnn
>PCG ← MAIN, SUB1, SUB2 altmode
(P.G and C options to print out core map.
Altmode is necessary. Loader looks for files
MAIN BIN, SUB1 BIN and SUB2 BIN on DEC tape)
↑S ctrlS (Loader types ↑S when loading is complete.
User must type 'ctrlS' to start program)
etc
These commands load a core image of a program. For example, suppose that a file FISHY DMP on DECtape unit 2 contains a core image of program. Load it as follows:-
$A DT2 -14 (Core image is read via -14) $GET FISHY DMP wait for DECtape to stop moving, then ctrlS etc. GETS would start the program without waiting for ctrlS.
GET without a file name would load the most recent dump. This and the process of dumping are described in the DOS user's manual (section 8.7); they would only be useful to someone developing a program.
Every program has its own set of error responses and the documentation for the program in question should explain them. Certain messages and events are more general and are described here.
A DOS error message consists of 'IOPS' followed by an integer error code followed possibly by more information. Some of these are frequent and the user should be aware of them.
If 'ctrlC' and reloading the program does not clear the condition, then try restarting the bootstrap (set 1.1 (f) ). Failing that, reload the bootstrap (step 1.1 (g) ). If reloading the bootstrap fails to clear the condition
(a) Record the occurrence in the log-book.
(b) Inform one of the operators.
There are other IOPS errors, which are unlikely to be encountered by someone just using programs; a PDP15 programmer may encounter them and should be able to deal with them (eg I0PS25 may mean a full disc, in which case some files must be deleted). A full list of errors can be found in Appendix D.1 of the DOS User's Manual. A summarized list is included in the DOS leaflet pinned on the notice board.
Example:-
$A <SYS> - 4 (Set up assignments for VIEW)
$A TT 4
$E VEIW (Mis-spell VIEW)
IOPSl3 DKL 03 SYS VEIW EXT
(The system failed to find VEIW XCT on the user
area <SYS> of the disc)
ctrlC
$A <SYS> - 4
$A PR 4 (Assign the paper tape reader to be the output
device for VIEW's messages)
$E VIEW (Program VIEW is attempting an illegal operation;
trying to write a message 'TAPE VIEWER' to the
paper tape reader)
ctrlC
DOS -15 Vnn
$A <SYS> - 4
$A TT 4
$E VIEW
TAPE VIEWER
←F 1
IOPS4 ctrlR (Device not ready; in VIEW, probably magnetic tape,
make it ready then 'ctrlR')
Program continues.
These errors appear on the teletype as
.LOAD n if using the linking loader (2.2.3) or .SYSLD n if loading a system program (2.2.1)
The error number n can be 1,2,3 or 4
If the computer stops or a peripheral becomes uncontrollable or some other inexplicable event occurs, try 'ctrlC'. If restarting or reloading the bootstrap fails, report the fault as in section 3.1.
MTDUMP is a program for performing simple tasks on ½" magnetic tape, viz, listing, copying and creating a software directory. It is described in the MTDUMP manual (reference 3). Users should be able to learn how to use MTDUMP by using this paper for information about DOS, by using this section (4.1) to find out what facilities are available and where they are described in the manual and by using the MTDUMP manual itself for a full description.
MTDUMP is normally loaded as follows:-
$A MTAn 1 (n is any number from O to 7, it is immaterial what the
the number is. Normally this assignment already exists.)
$A TT 3 (Slot 3 is the output device for MTDUMP listings. TT
is normal but can be varied)
$MTDUMP
MTDUMP Vnn
BUFSIZ m
> ('>' is the signal for the user to type an MTDUMP command)
At any point while this is going on, one or two tapes can be loaded.
Ignore the loading procedure in the MTDUMP manual, which uses the linking loader (2.2.3).
At anytime 'ctrlP' can be typed, to restart MIDUMP without going back to DOS.
MTDUMP provides a BACKSPACE (B), REWIND (R), SPACE (S) and TAPEMARK command. Example:-
>R 2 (Rewind tape unit 2) >T 2 ( 1 filemark) >T 2 >R 2 (To BOT) >S 2 (Space unit 2 by 1 record) >S 2,EOF (Space unit 2 until EOF is passed >B 2,2 (Backspace to BOT) >S 2,2 (Space forward 2 records) >R 2 (Return to BOT)
Read section 3.1 and 3.3 of the MTDUMP manual.
It is possible to set parity (0 or E) and density (2, 5 or 8) for subsequent reading and writing with the FORMAT command. Default is 0 and 5. Example:-
>F 1,08 (Format of unit 1 is to be odd and 800 bpi) >F 1,80 (Same effect) >F 12,E (The 2 units can be different; density is unchanged)
There is a LIST command (section 3.4 of MTDUMP) for typing records on the teletype and a COPY command (section 3.5 of MTDUMP) for transferring records from one tape to another. A copy or a list can be terminated by a record-count, EOF or EOT (like SPACE and BACKSPACE). A long copy or list can be terminated by 'ctrlP' but the exact tape positions after 'ctrlP' are undefined.
The VT ON facility can be used (see section 2.1.10 of this paper).
Records can be dumped onto a DECtape file using the DUMP command (section 3.4 of MTDUMP); this requires an assignment of DTn (where n is the DECtape unit number) to slot 3 in DOS. This DECtape file can then be listed on the 1906A lineprinter using the LISTIT system (reference 6). A disc file should not be used; at present the facility does not work.
The program prints a message when it hits an irrecoverable read error.
This is a pair of programs for producing computer animated movies. CAMP is 2-D only; CAMPER can manipulate 3-D objects. They are fully described in the CAMP and CAMPER manual (reference 4); chapters 1,2,3 describe the programs and section 4.3 describes the particular case of the PDP15.
The FONTS program allows a user to design characters using the lightpen and to design slides or title pictures using these characters or previously designed ones. Description is in SPROGS PAPERS 17 and 23 (reference 5).
The purpose of LISTIT is to transfer character files from any PDP15 device to the 1906A 1ineprinter via ½" tape, not via the BSI. It is described in SPROGS TECHNICAL PAPERs 10 and 13 (reference 6).
The purpose of VIEW is to display on the VT15 frames which are recorded on magnetic tape in SD4020 format. It is described in SPROGS TECHNICAL PAPER 9 (reference 7). That paper also includes a description of how to use DOS (section 2), but that is superseded by this paper.
Whenever the system teletype is used for input, there are some control characters available.
The control key (CTRL)
The convention 'ctrl*', where* is some letter in the list below, is used in this document to mean:-
"press the key marked 'CTRL' and while it is pressed down hit the letter. DOS will 'echo' the keystroke as below".
INPUT ECHO MEANING
INPUT
'ctr1C' ↑C current program is terminated and control is returned to DOS
'ctr1P' ↑P interrupt the program; the precise action for any program is
described in the documentation for the program program. MTDUMP restarts itself (4.1).
'ctr1R' ↑R If DOS types 'IOPS 4' this means some device is not ready to
be used by the program (probably ½" tape). Make the
device ready and type 'ctrlR'.
'ctr1S' ↑S start the program; normally used when the linking loader has
finished loading (2.2.3); also, for some programs this is a
useful method of causing a restart.
'ctr1U' @ the whole of the current line is deleted from the input buffer;
typing at the keyboard can begin again.
'ctr1X' ↑ or controls text output on display if VT ON has been used -
nothing brief mention in 2.1.10.
Rubout
If you press the RUBOUT key, before 'return' or 'altmode', then the previous character is deleted. For example:-
ABCDruboutruboutEF will put ABEF into the input buffer. DOS will echo /; the hard copy will look like
ABCD//EF
Terminators
No command is acted upon by the system unless a line terminator is typed (RETURN key or ALTNODE key). Therefore before the line terminator is typed, rubout and 'ctrlU' can be used.
(1) Twist the top hub anticlockwise to loosen it.
(2) Put the tape reel around the hub, make sure it is flat and tighten the hub again. If the tape is not flat, then it will revolve crookedly. VIEW does not write to the tape, so the write-permit ring can be removed. The gap it leaves must be inwards.
(3) Wind off some tape until is almost reaches the floor.
(4) Guide the tape between the 2 white covers and bring the end onto the top of the take up reel. The tape should be straight all the way through and must be entirely the other side of the glass vacuum cover, so that nothing prevents the tape being drawn into the vacuum at step 7.
(5) If power is not already on, press POWER switch.
(6) Press and hold START/BRAKES switch to BRAKES. This releases the brake and will allow you to turn the take-up reel clockwise. With ingenuity, keep hold of the tape while turning the take-up reel 3½-4 revs. Release the BRAKES-switch.
(7) Press START/BRAKES switch to START this will cause the tape to be drawn into the vacuum chambers. The door can now be closed.
(8) Dial the thumbwheel unit number to 1 for VIEW program.
(9) In the top row of switches, press FORWARD and, when the tape has stopped moving, ONLINE. If tape continues to move indefinitely, load-point must already have been passed. Therefore, press RESET and REWIND to bring it back. When it stops press ONLINE.
(10) The tape is now ready to be accessed by the program. Check that, of the lights in the top row, LOAD, RESET, ONLINE & POWER are alight and that, of the lights in the top right READY, LOAD-POINT, 7, WRITELOCK (if no write-ring) and (possibly) SELECT.
(1) Press OFFLINE.
(2) If tape is not at load-point (see top right set of lights), then press REWIND (unless tape is known to be before load-point).
(3) Press and hold START/BRAKES to BRAKES and wind the top reel anti-clockwise until all the tape is on the top reel. Note that the brakes take an instant to release themselves.
(4) Twist the top hub anti-clockwise to loosen it, remove the tape reel and retighten the hub.
(5) If no more tapes POWER OFF.
(1) Note that Reader has shiny knob in centre. Turn it clockwise to lift a black movable plate in the mechanism.
(2) Note that reader has a fanfold tape holder either side of the mechanism in the centre. Put fan-fold tape in right-hand holder.
(3) Take hold of the leading piece of tape and check that (a) the leading line of holes is off centre away from you and (b) the line of arrows printed on the tape is towards your left. Otherwise turn the tape around until it is correct.
(4) Lay the leading piece of tape immediately under the fixed black plate and over the toothed wheel; the teeth should fit the holes.
(5) Turn the shiny knob anti-clockwise to lower the black movable onto the tape; the teeth should still fit the holes.
(6) Ensure that Reader switch is ON.
(7) Press FEED button (for READER not PUNCH) sufficiently long for some blank tape to be sitting in left-hand holder, but obviously no non-blank tape should pass underneath the fixed plate.
(8) Paper tape is now ready to be read by the computer.
Not all the tape will pass through after being read by the computer. To unload either (a) press the feed button until it is all through, or (b) turn the knob to lift the movable plate and lift the tape out.
The central console of the PDP15 is the array of switches and lights with a working surface in front. A diagram of the switches is shown below and those features mentioned in this document are labelled.
The address switches are used in loading a paper tape program (like the bootstrap or hardware test program), or in re-starting the computer (section 2.2). A switch set with the stripe showing is a bit set to 1 in the number representing the address. When we refer to this number (or when the DEC manuals do), the bits will be grouped into three's; in other words, it will be expressed in octal. The address in the diagram therefore, is 77646.
Each bit of the data switches can be read by a program. Only bits 0 to 3 are used by VIEW. In the diagram, switches 0, 2 and 3 are set.
The ON/OFF switch for the computer is turned clockwise. for ON and anti-clockwise for OFF. The ½" tape decks are switched on/off separately. The control teletype is switched off automatically when the computer is switched off.
This appendix gives a list of PDP15 peripherals mentioned in this document with the abbreviations that are understood by the software. In particular, these abbreviations are used in assignment commands (sections 2.4 and 5).
(1) PDP15/20 User's guide: Advanced Monitor Software System (DEC-15-MG2B-D) (The Advanced Monitor is the system ACL used prior to DOS. The pocket book Users Guide describes most of the DOS commands, however.) (copy in PDP15 area)
(2) PDPl5 DOS Users' Manual (DEC-I5-MRDA-D) (Copy in PDP15 bookcase)
(3) MTDUMP utility program (DEC-I5-YZB-NA) (copy in PDPl5 Bookcase)
AC1 Software (briefly mentioned in sections 4.2 to 4.5)
(4) CAMP and CAMPER on the 1906A and PDP15 (from the library)
(5) SPROGS PAPERS 17 and 23 on FONTS (from Basic Software)
(6) SPROGS TECHNICAL PAPERS 10 and 13 on LISTIT from Basic Software)
(7) SPROGS TECHNICAL PAPER 9 and SPROGS PAPER 13 on VIEW (from Basic Software)