Create a PDP-8 OS8 RK05 system disk from RX01 floppies with SIMH (and get text files in and out of the PDP-8)
Published: 07-12-2016 | Last update: 07-05-2019 | Author: Remy van Elst | Text only version of this article
❗ This post is over two years old. It may no longer be up to date. Opinions may have changed.
Table of Contents
PDP-8/L with papertape reader (src)
This guide shows you how to build an RK05 bootable system disk with OS/8 on it for the PDP-8, in the SIMH emulator. We will use two RX01 floppies as the build source, copy over all the files and set up the LPT printer and the PTR/PIP paper tape punch/readers. As an added bonus the article also shows you how to get text files in and out of the PDP-8 sytem using the printer and papertape reader / puncher.
Oscar Vermeulen created an amazing replica of the PDP-8/I. It's a front panel with working switches and LED's, plus a simple Raspberry Pi running the SIMH emulator. I've written multiple articles on the PDP and PiDP-8 and I like the device a lot in general.
Consider sponsoring me on Github. It means the world to me if you show your appreciation and you'll help pay the server costs.
You can also sponsor me by getting a Digital Ocean VPS. With this referral link you'll get $100 credit for 60 days.
You need simh installed. On Ubuntu this can be done with
apt-get install simh
On Arch linux with
pacman -Sy simh
You also need two RX01 floppy disks with the OS/8 system on them. We will use
those floppies to create and format an RK05 disk and copy over all the files. As
a bonus we will also copy over a lot of games from the famous
Create a new folder for this project:
mkdir pdp8-buildsys cd pdp8-buildsys
Download the two floppies:
wget http://www.pdp8online.com/ftp/images/os8/os8_rx.rx01 wget http://www.pdp8online.com/ftp/images/os8/os8f4_rx.rx01
The files are mirrored here as well:
wget https://raymii.org/s/inc/downloads/pdp/os8_rx.rx01 wget https://raymii.org/s/inc/downloads/pdp/os8f4_rx.rx01
The first disk is OS/8 with Basic, the second disk with Fortran 4.
advent disk as well:
OS/8 was delivered via a lot of different ways. You could get it on paper tape,
DECtape, RK05 disks or RX01/2 floppies. All 'distributions' came with a utility
named BUILD, which allowed you to create new systems or modify the existing
running system. In our case we use the RX01 floppies as our 'source', booting of
one of them. We then use the
BUILD program to format a new RK05 disk and then
copy over all the programs.
On the left an RX01 or RX02 diskette and on the right an RX50 diskette. (source)
Update 2019-05-07, thanks to Doug. Doug wrote in, quoting verbatim:
The RX01 and RX02 are both 8 inch diameter floppy disks. They are single sided media. The RX50 is a 5.25 inch single sided diskette with 10 sectors per track and 80 tracks. There were 512 bytes per sector making this about a 400kb diskette. The diskette on the left is the RX50 and the diskette on the right is either an RX01 or RX02. The RX01 was formatted in an industry standard with 26 sectors and 77 tracks. Each sector was 128 bytes. The RX02 has 256 bytes per sector. The RX01 could hold 256kb and the RX02 could hold 512kb. I never saw an RX50 on a PDP-8. There was no support for it in OS/8 V3.
We will not create a simh ini file just yet. Fire off the emulator in this folder:
First we will tell the emulator that it is emulating a PDP8 with 32k of core memory (instead of 4):
PDP-8 simulator V4.0-0 Beta git commit id: ff95fb8e sim> set cpu 32k sim> set cpu noidle
Attach the (nonexistent) new system disk, simh will create it:
sim> attach rk0 systemdisk.rk05 RK: creating new file
Attach the two existing floppy images:
sim> attach rx0 os8_rx.rx01 RX: buffering file in memory sim> attach rx1 os8f4_rx.rx01 RX: buffering file in memory
Last but not least, the
sim> attach rk1 advent.rk05 sim>
All is set up, we're ready to boot into OS/8 from the floppy.
RUN SYS BUILD
It is time to boot up the system from the floppy disk:
sim> boot rx0 .
If you see the
. (dot), then it works and you're in OS/8. Test it out:
.RESORC /L 1 FREE BLOCKS NAME TYPE USER SYS RX8E DSK RX8E PTR PTR RXA0 RX8E RXA1 RX8E RKA0 RK8E RKB0 RK8E RKA1 RK8E RKB1 RK8E TTY TTY LPT LPTR OS/8 V3Q .
RESORC command shows the system resources. In this case we can see that
SYS (system partition?) is of type
RX8E. This type is the subsystem
controller (hardware board) which, via the OMNIBUS, drives the RX01 floppy
drive. RK8E is the (OMNIBUS) controller for the
RK05 disks. The
is the paper tape/punch used with
PIP as the
We start with formatting the disk with the
.ZERO RKA0: .ZERO RKB0: .
RKA0 and RKB0 represent the inner and outer cylinders of the disk. The split is necessary because OS/8 cannot address the entire 2.5 MB disk with a 12-bit machine word. 1.6 megawords is 6250 sectors (256 words per sector) so that overflows the 4096 word limit. So, it just assigns half the disk to one device, and half to the other.
On the RK05F, the double-capacity fixed-disk version, OS/8 sees two logical drives, drive 0 and drive 1. So, RKA0, RKB0, RKA1, and RKB1.
The above disk explanation comes via Warren Young and Rick Murphy on the PiDP-8 mailinglist.
The actual system build is done with the
.RUN SYS BUILD $
From the OS/8 System reference manual (AA-H607A-TA OS8 V3D_sysMan), Chapter 9,
the description of
BUILD is the system generation program for OS/8 that allows you to:
- Create an OS/8 monitor system from cassettes or paper tapes.
- Maintain and update device handlers in an existing OS/8 system.
- Add device handlers supplied by DIGITAL to a new or existing system.
- Add your own device handlers to a new or existing system.
BUILD, you use simple keyboard commands to manipulate the device handlers
that make up the OS/8 peripheral configuration.
BUILD allows you to quickly
and easily insert devices not standard on the system.
Device handlers are comparable to our current day device drivers. They for example know how a specific disk, paper tape or other device works and let the OS/8 system use it.
I'll go over a few commands in more detail below. After that we create the actual disk with the commands.
$PRINT PT8E: PTP *PTR RX8E: *SYS RX01: *RXA0 *RXA1 RK8E: SYS RKA0 RKB0 RK05: *RKA0 *RKB0 *RKA1 *RKB1 RKA2 RKB2 RKA3 RKB3 KL8E: *TTY LS8E: *LPT DSK=RX8E:SYS
If there is an asterisk (
*) in front of the devices then that device is active
and will be included in the new OS/8 system.
SYSTEM are used to activate
device handlers. A maximum of 15 handlers, including the system device (SYS) and
the default mass storage device can be made active.
If you have a tape with a specific device handler, which will be unlikely in the
simh emulation, you can use the
LOAD command to load this handler
from the tape device. For example to load a handler from a binary paper tape:
$LOAD PTR: ^ $
The caret (
^) is shown to indicate that the system is waiting for the tape to
be loaded. If you've loaded the device then you can press any key (the ESC is a
good one). The prompt will change back to
$ to indicate that the handler has
been loader. If you have a specific filename on a structured device you can
specify it after the colon. A paper tape is a non-structured device so we can
omit it there.
To load the handler with the filename
HANDLR.03 from the DECtape device
use the below syntax:
$LOAD DTA3:HANDLR.03 $
INSERT and DELETE
LOAD command has made a handler or group of handlers available for
insertion into the OS/8 system, use the
INSERT command to make particular
entry points active. The
INSERT command uses two arguments;
Gname is the group name of the handler, for example, the
TC08 DECtape is
Pname is the permanent name by which the device is
currently known to
BUILD. TC08 DECtape thus has the group name
TC and the
Other examples are to include a handler for the paper tape reader and punch
$INSERT PT8E:PTR $INSERT PT8E:PTP
If you want to export files or import files (with PIP) then having the papertape reader is quite handy.
DSK allows you to specify the name of the device that will become the default
storage device of OS/8. Since we want to use the RK05 disk, we should tell the
SYSTEM and BOOTSTRAP
SYSTEM command specifies devices that are system handlers. The
command is the command that finally implements all the changes that you made
BOOT rewrites all relevant Monitor tables and device handlers to
reflect the updated system status. The devices
BUILD had marked active now
become device handlers in the system.
To mark the RK05 drive as the system device:
$SYSTEM RK8E $BOOT WRITE ZERO DIRECT?YES SYS BUILT
If the system device specified is different from the current system device,
BUILD copies the system from the current system device to the new system
device. After the copy is complete,
WRITE ZERO DIRECT?
to determine whether a new (zero) directory is to be writtenon the new system device. If the reply is YES, the system will place a zero directory on the device. Any other reply causes the system to retain the old directory.
We must save the built system in the case we ever want to make changes to it
again without starting over. This is after you've exited the
(with CTRL+C), in the OS/8 prompt:
. SAVE SYS BUILD
BUILD the new device
If you've read all the above information you can probably guess the commands
we're going to execute. We start from the OS/8 monitor (
. prompt) by running:
. RUN SYS BUILD
The prompt changes to the
$. Delete the current system device (we don't want
the floppy-based system, but the disk based one):
Make the RK8E device the active system handler:
Also make the RK8E device the active handler for the RK[A|B]0 disk:
$INSERT RK8E:RKA0 $INSERT RK8E:RKB0
The papertape reader and punch and the LPT printer always come in handy, so insert the required system handlers:
$INSERT LS8E:LPT $INSERT PT8E:PTP $INSERT PT8E:PTR
Mark the RK8E handler the primary disk:
$DSK RK8E:SYS $SYSTEM RK8E
If you get the error:
Then you need to check if the RX8E (floppy) handler is not active. Issue the
RX8E: *SYS RK8E: *SYS *RKA0 *RKB0
* (star) is there, it is active. Run
DELETE SYS again and check with
RX8E: SYS RK8E: *SYS *RKA0 *RKB0
Run BOOT again and it should work.
.SAVE SYS BUILD
Copy all the things
The systemdrive is set up on the RK05 disk, we can now boot from it. Press
CTRL+E to pause and return to the SIMH prompt and boot from the new system
Simulation stopped, PC: 01210 (JMP 1207) sim> boot rk0 .
Any command will fail, since there is nothing on the device except the bare base system:
.DIR NO CCL! .RES /L NO CCL! .
We should copy over all the system files and software from the floppy drive.
CTRL+E again and boot from the floppy disk again:
Simulation stopped, PC: 01210 (JMP 1207) sim> boot rx0 .
DIR command you can see what is on the disk. I made a typo earlier
SAVE SYS BUILD as you can see:
.DIR RKA0: BUILT .SV 33 BUILD .SV 33 2 FILES IN 66 BLOCKS - 3126 FREE BLOCKS
The other side of the disk is empty as well:
.DIR RKB0: 0 FILES IN 0 BLOCKS - 3241 FREE BLOCKS
Copy over all the files from disk A:
The syntax is
COPY DEST:<SRC:name.ext. To just copy the binaries you can do
The output is a list of files copied:
FILES COPIED: ABSLDR.SV BITMAP.SV [...] BATCH.SV FUTIL.SV IDS.SV .
The second floppy has the FORTRAN compiler. Copy that over as well:
The same output is given, the list of files and such:
FILES COPIED: BUILD.SV CCL.SV DIRECT.SV EDIT.SV FOTP.SV F4.SV FORLIB.RL [...]
We also have the
ADVENT disk coupled. It houses a few programs I want, like
WPFLOP.SV (to manage WPS-8 diskettes) and the editor
TECO.SV. Copy that as
Here I copy just the programs, nothing else. The B side of that disk has the
ADVENT.SV game and a boatload of other games, if you like you can copy it as
You might hit a full disk and get errors like these:
NO ROOM, SKIPPING- RX01SY.BN
DIR RKA0: command you can see large files (blocks used). With the
DEL command you can remove them:
.DEL RKA0:ADVENT.TX FILES DELETED: ADVENT.TX
I also don't want the
FILES DELETED: MUSIC5.MU USA.MU JCOOK2.MU SCALE.MU JCOOK1.MU BABYEL.MU MUSIC2.MU MUSIC3.MU MUSIC4.MU MUSIC1.MU MUSIC6.MU FIFTH3.MU FIFTH1.MU MINUET.MU YANKEE.MU FUGUE.MU CASCAD.MU MAPLE.MU ENTER.MU GMINOR.MU
Do more file management as you like. To see the contents of a file, use the
1 PRINT "DIRECT YOUR DOG TO ANY OF THE FOLLOWING FILES:" 2 PRINT "1=KEYBOARD,2=LINE PRINTER,3=HIGH SPEED PUNCH" 3 PRINT "WHICH ONE";\INPUT A [...]
When you're done we can finish off by booting from the filled up
CTRL+E to return to the simh prompt and boot off the disk:
Simulation stopped, PC: 01207 (KSF) sim> boot rk0 .
Check that the new system runs from the disk with the
.RESOURC /L 614 FREE BLOCKS NAME TYPE USER SYS RK8E DSK RK8E PTP PTP PTR PTR RXA0 RX8E RXA1 RX8E RKA0 RK8E RKB0 RK8E RKA0 RK8E RKB0 RK8E RKA1 RK8E RKB1 RK8E TTY TTY LPT LPTR OS/8 V3Q
The version command:
.VERSION OS/8 - KBM V3Q - CCL V1F
SNOOPY script to get a nice ASCII suprise:
.R BASIC NEW OR OLD--OLD FILE NAME--SNOOPY.BA READY RUN SNOOPY BA 5B DIRECT YOUR DOG TO ANY OF THE FOLLOWING FILES: 1=KEYBOARD,2=LINE PRINTER,3=HIGH SPEED PUNCH WHICH ONE?1 [...] COMPLIMENTS OF DIGITAL'S PDP-8/E COMPUTER READY
Punching and reading PAPERTAPE with PIP aka getting files in and out of the
Now that we have a working systemdisk we can set up a
simh.ini file and play
with the papertape reader and puncher. This is the contents of my simh ini file:
set cpu 32k set cpu noidle attach ptr ptr.txt attach ptp ptp.txt set lpt enable attach lpt lpt.txt attach rk0 systemdisk.rk05 boot rk0
If you start the sim it will create the text files:
$ simh-pdp8 pdp8.ini PDP-8 simulator V4.0-0 Beta git commit id: ff95fb8e PTR: creating new file PTP: creating new file LPT: creating new file .
To get files off the PDP-8 system, use the
PTP device (paper tape punch).
Create a test file with the
I to Insert text in the current like:
#I HELLO RAYMII.ORG HOW ARE YOU?
CTRL+L to exit EDIT mode:
L to list the contents:
#L HELLO RAYMII.ORG HOW ARE YOU? .
Save the file with
TYPE command you can also check the contents:
.TYPE REMY.TX HELLO RAYMII.ORG HOW ARE YOU? .
Fire up the
PIP program, it stands for
peripheral interchange program. I
didn't make it up, but the name is quite a mouthfull. Just as with the copy
command, we can send data from place A to place B:
The prompt changes to a
*. Send the text file to the
Or to the papertape punch:
Syntax is like
DEST:<SRC. Press ESC afterwards to return to the OS/8
Exit SIMH (
BOOT /DT) or just
CTRL+E and check the printer text file:
$ cat lpt.txt HELLO RAYMII.ORG HOW ARE YOU? .
To get files into the system, like your assembler or basic programs, use the
PTR (reader). On the host system, edit the
ptr.txt file with your desired
$ cat ptr.txt Raymii.org The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog.
The file does require DOS line endings, so convert it:
$ unix2dos ptr.txt unix2dos: converting file ptr.txt to DOS format...
Start up simh again and fire up PIP. The syntax here is the opposite of when getting data out of the system, since we now have our local file as the DEST:
.R PIP *REMY2.TX<PTR:
The prompt now changes to an
^. This is to allow you to load the paper tape.
Since we're emulating that is not needed. Press
ESC to continue, the prompt
will go back to the
^* *^C .
Since the encoding is different the file is in ALL CAPS, but that's not an issue for compiling:
.TYPE REMY2.TX RAYMII.ORG THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG. THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG. THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG. .
There is one more way to get text in the system, directly via the terminal.
TTY device on emulated PDP-8's is just a window on your host
computer, you can use the
TTY device in
PIP and paste text in from the host.
Start up pip in OS/8:
. R PIP
then use the "FILE.EX<TTY:" as input to PIP:
Paste the text and ype
CTRL+Z when the input is done. There is a 140 character
line limit in ASCII mode. If you have binary data or longer lines, start up
PIP with the
/I flag in Image Mode.
The above TTY trick comes via Warren Young and Rick Murphy on the PiDP-8 mailinglist.
When your entirely finished with your newly built system drive you can shut down
the system with the
BOOT command, then quit SIMH with a
Tags: articles , dec , pdp , pdp-8 , pidp8 , rk05 , rx01 , simh , wps-8
HALT instruction, PC: 00002 (JMP I 177) sim> ^C