PDP-11 C for RT-11 ?

[Neal G.]

Where can I find the installation media kit?

Or maybe an RT-11 image with it already built and ready to go?

Thanks in advance.

[Clem Cole]

https://github.com/rust11/discuss

As an FYI:  Index of /RT-11/freeware/sigtapes/11sp68  - This server contains raw sector-by-sector disk images of the original DECUS distributions.

This is a directory of the original individual logical disk images (501.DSK through 606.DSK) containing the complete, unedited MACRO-11 and C source codes written by Martin Minow and David Conroy

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[Johnny Billquist]

That's DECUS C, which is not what the OP was asking for.

There is https://ftp.trailing-edge.com/pub/rt_dists/layered/, but I
haven't checked if that one actually is correct, but it looks like it.

Johnny

On 2026-05-14 21:35, Clem Cole wrote:
> https://github.com/rust11/discuss <https://github.com/rust11/decusc>

>
> As an FYI: Index of /RT-11/freeware/sigtapes/11sp68  - This server
> contains raw sector-by-sector disk images of the original DECUS
> distributions.
> This is a directory of the original individual logical disk images(|

> 501.DSK| through |606.DSK|) containing the complete, unedited MACRO-11

> and C source codes written by Martin Minow and David Conroy
>
> On Thu, May 14, 2026 at 12:12 PM Neal G. <cven...@earthlink.net
> <mailto:cven...@earthlink.net>> wrote:
>
> Where can I find the installation media kit?
> Or maybe an RT-11 image with it already built and ready to go?
> Thanks in advance.
>
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> pidp-11/347b9e4c-871b-4a16-9004-3c27275e8691n%40googlegroups.com?
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>
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--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: b...@softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol

[isy...@gmail.com]

Hi Neal,

 This will hopefully get you started with Decus c:

 1. Manual: https://drive.google.com/file/d/1voVSkjdG8nCCsiwxRGPFbHYYFvo2ozE-/view?usp=sharing

 2. RT11 image: https://drive.google.com/file/d/11nepCeBE2QVQVG7OIIWkYjSBRd791Hwz/view?usp=sharing

 To test, boot this RK05 image,

 . del pdp8.sav

 .@pdp8.com

<several messages>

 . r pdp8

 Argv:(press return)

 ->B

->R 200

.FCL

 (and have a good laugh)

See manual for required files and look at pdp8.com for an example compile. NB You do not need qopen for anything you might try.....

Regards, Ian.

[Neal G.]

Thanks Ian,

"YOU HAVE SUCCESSFULLY LOADED 'FOCAL,1969' ON A PDP-8 COMPUTER." 

Yes, I got a laugh out of that.

It is interesting to look over the work that others have done; though, as Johnny discerned, I was looking for DEC's PDP-11 C.

I had already taken a look at DECUS C from the archives on the freeware CDROM image from bitsavers.

Regards,

Neal G. 

On Monday, May 18, 2026 at 6:10:29 AM UTC-5 isy...@gmail.com wrote:

This will hopefully get you started with Decus c:

[isy...@gmail.com]

Excellent! I would note that I am not quite sure where DEC's definitive RT11 c compiler is. There are various links to

the original K&R code about the place but I have not seen it all put together for RT11. The nearest I have is

in the UNIX builds and I think the best/stable (???) version is in the last version of Ultrix for the PDP11 ... V3.x.

If you make any progress here, do let us all know.

BW, Ian

[Clem Cole]

Answering a few questions WRT the official compiler vs the DECUS C compiler, please note that I previously answered that the DECUS compiler will work on a traditional RT-11 system (a.k.a., RT-11/SJ or RT-11/FB).  But the OP did ask about the official layered product, as did Ian; I'll offer a more complete answer.  It's a bit more complicated.

Also, I note that the target system for the DEC layered product (PDP-11 C) requires a PDP-11 with an MMU and running what DEC called RT-11/XM with at least 256K of memory.  I'm going to assume you have sysgen'ed an RT-11/XM and set up OpenSIMH for a PDP-11 with an MMU.

Before I got further, https://web.archive.org/web/20220928104818/http://mim.stupi.net/manuals/LAYERED/ has four files: 

PDP-11 C V1.2

• AV-NA47D-TC Cover Letter [pdp11c1.pdf]
• AA-NA46D-TC Installation Guide [pdp11c2.pdf]
• ??? Guide to PDP-11 C [pdp11c2.pdf] - I believe this is some version AV-NA45x-TC
• ??? PDP-11 C RTL Reference Manual [pdp11c2.pdf] - I believe this some version AV-NA45x-TC

Unfortunately, the 4th file is corrupt (and seems to have been that way for several years, it seems), and I have not found a copy AV-NA45x-TC [the RSTS Guide to documentation lists it as AV-NA45A-TC]

The directory https://ftp.trailing-edge.com/pub/rt_dists/layered/ is believed to contain many of the DEC layered products. including: rt11_c_v1_1.zip, 

which is a zipped file of a virtual tape rt11_c_v1_1.tpc     

Given that this is a tpc format file, I will wager that it's either a copy of the 9-track image or the TK50.

The good news is that OpenSIMH can understand all of TAP, TPC, E11 or P7B virtual tape formats. You can also use either the older mtcvtv23(1) or the newer tpc2mt(1)  tools to create a native TAP format file.

If you leave it as TPC format, the command to sim> attach -r -F TPC <YOUR TAPE DEVICE>  rt11_c_v1_1.tpc  will mount the tape (readonly).  If you convert to TAP first, the -F TPC is not needed.  Either way, you need to replace <YOUR TAPE DEVICE> with one of:

• MS0 for a TS11/TS05 using the RT11 MS.SYS device driver and OpenSIMH TS device.
• MU0 for a TK50/TU81 using the RT11 MU.SYS device driver and OpenSIMH TQ device.
• MT0 for a TM11/TU10 using the RT11 MT.SYS device driver and OpenSIMH TM device.
• DT0 for a DECtape using the RT11 DT.SYS device driver and OpenSIMH TC device.

What I cannot tell you for sure, because I have not investigated/tied it myself, is the format the RT11 is expecting.   But if you look at the second file listed above (AA-NA46D-TC Installation Guide [pdp11c2.pdf])

started on Page 6-1  — Chapter 6 - Installing PDP–11 C on a RT–11 Operating System 

According to that page, DEC released PDP-11 C on one of an RL11, a 1600 BPI 9-track, a TK50, 6 RX50 diskettes, or 10 RX01 diskettes. 

Assuming you have booted RT-11/XM, make sure you have a tape configured in openSIMH, and a tape device driver is loaded.   To do that type: show devices  to list all devices currently installed and configured in the operating system's device table. Look for your device prefix (e.g., MS, MU, MT, DT in the left-hand column).  Then type: show sub  to list the currently loaded subsystem table, identifying which drivers are actively resident in memory or available for system execution.  If you don't see one, then type: install xx where xx is one of MS, MU, MT, or DT

Moving to page 6-4 and assuming this is a tape image:

6.2.2 Installing from Tape

To install PDP–11 C from a 1600 bpi magtape kit or TK50 tape cartridge, place

the PDP–11 C distribution medium in the drive and then issue the following

DCL command:

backup/restore/sys indev:pdp11c/saveset,*.* outdev:

indev: The device name where you mounted the PDP–11 C distribution medium.

outdev: The installation device name (the device where you wish to install PDP–11

C). If you desire a standard installation of PDP–11 C, specify SY: as the

installation device.

So, assuming you are using the TM11:   backup/restore/sys mt0:pdp11c/saveset,*.* SY: 

Good luck,

Clem

[Johnny Billquist]

The DEC PDP-11 C compiler is a ANSI C89 compliant compiler. So not K&R.

DECUS C is an early K&R, and at least Alan Baldwin (who did TCP/IP for
RT-11 and TSX) distribute a bug fixed version of DECUS C with his TCP/IP
package. See https://shop-pdp.net/index.php for more information.

But as for the DEC PDP-11 C compiler, I at least found one possible disk
image of it for RT-11. It's easier to find for RSTS/E or RSX (I created
an RPM for the RSX version).

Johnny

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[Johnny Billquist]

The "fourth file" is not corrupted at all. Maybe the wayback machine
copy is (haven't looked), but the one on MIM is certainly not corrupted.

However, Mim is nowadays on Mim.SoftJAR.SE, and not Mim.Stupi.SE.

But the backstory of those two manuals are that I found them many years
ago online, apparently from a VMS documentation set in docbook format
(then converted into PDFs by some tool), which is why they are slightly
annoying. I do have the paper manuals myself, and sometimes I wonder if
I should scan them. But all the actual information is in the online
versions, so it's not really a high priority thing.

Johnny

On 2026-05-19 04:57, Clem Cole wrote:
> Answering a few questions WRT the official compiler vs the DECUS C
> compiler, please note that I previously answered that the DECUS compiler

> will work on a traditional RT-11 system (/a.k.a/., RT-11/SJ or RT-11/

> FB).  But the OP did ask about the official layered product, as did Ian;
> I'll offer a more complete answer.  It's a bit more complicated.
>
> Also, I note that the target system for the DEC layered product (PDP-11
> C) requires a PDP-11 with an MMU and running what DEC called RT-11/XM
> with at least 256K of memory.  I'm going to assume you have sysgen'ed an
> RT-11/XM and set up OpenSIMH for a PDP-11 with an MMU.
>
> Before I got further, https://web.archive.org/web/20220928104818/http://

> mim.stupi.net/manuals/LAYERED/ <https://web.archive.org/

> web/20220928104818/http://mim.stupi.net/manuals/LAYERED/> has four files:
>
> PDP-11 C V1.2
>

> * AV-NA47D-TC Cover Letter [pdp11c1.pdf]
> * AA-NA46D-TC Installation Guide [pdp11c2.pdf]
> * ??? Guide to PDP-11 C [pdp11c2.pdf] - I believe this is some
> version AV-NA45x-TC
> * ??? PDP-11 C RTL Reference Manual [pdp11c2.pdf] - I believe

> this some version AV-NA45x-TC
>
> Unfortunately, the 4th file is corrupt (and seems to have been that way
> for several years, it seems), and I have not found a copy AV-NA45x-TC
> [the RSTS Guide to documentation lists it as AV-NA45A-TC]
>
> The directory https://ftp.trailing-edge.com/pub/rt_dists/layered/
> <https://ftp.trailing-edge.com/pub/rt_dists/layered/> is believed to

> containmany of the DEC layered products. including: rt11_c_v1_1.zip,

> which is a zipped file of a virtual tape rt11_c_v1_1.tpc
>

> Given that this is a tpcformat file, I will wager that it's either a

> copy of the 9-track image or the TK50.
>
> The good news is that OpenSIMH can understand all of TAP, TPC,E11or

> P7B virtual tape formats. Youcan also use either the older mtcvtv23(1)
> or the newer tpc2mt(1)  tools to create a nativeTAPformat file.

>
>
> If you leave it as TPC format, the command to sim>attach -r -F TPC <YOUR
> TAPE DEVICE>  rt11_c_v1_1.tpc will mount the tape (readonly). If you

> convert to TAPfirst, the -F TPCis not needed.  Either way, you need to

> replace<YOUR TAPE DEVICE>with one of:
>

> * MS0 for a TS11/TS05 using the RT11MS.SYS device driver and OpenSIMH
> TS device.
> * MU0 for a TK50/TU81 using the RT11 MU.SYS device driver and OpenSIMH
> TQ device.
> * MT0 for a TM11/TU10 using the RT11 MT.SYS device driver and OpenSIMH
> TM device.
> * DT0 for a DECtape using the RT11 DT.SYS device driver and OpenSIMH

> TC device.
>
> What I cannot tell you for sure, because I have not investigated/tied it
> myself, is the format the RT11 is expecting.   But if you look at the
> second file listed above (AA-NA46D-TC Installation Guide [pdp11c2.pdf])

> started on Page 6-1  — *Chapter 6 - **Installing PDP–11 C on a RT–11
> Operating System *

>
> According to that page, DEC released PDP-11 C on one of an RL11, a1600
> BPI 9-track, a TK50, 6 RX50 diskettes, or 10 RX01 diskettes.
>
> Assuming you have booted RT-11/XM, make sure you have a tape configured
> in openSIMH, and a tape device driveris loaded.   Todo that type: show

> devicesto list all devices currently installed and configured in the
> operating system's device table. Look for your device prefix (/e.g./,
> MS, MU, MT, DT in the left-hand column).  Thentype: show subto list the

> currently loaded subsystem table, identifying which drivers are actively
> resident in memory or available for system execution.  If you don't see

> one, then type: installxxwhere xxis one of MS, MU, MT, or DT

>
> Moving to page 6-4 and assuming this is a tape image:

> *
> *
> *6.2.2 Installing from Tape*

>
> To install PDP–11 C from a 1600 bpi magtape kit or TK50 tape
> cartridge, place
>
> the PDP–11 C distribution medium in the drive and then issue the
> following
>
> DCL command:
>

> backup/restore/sys /indev:/pdp11c/saveset,*.* /outdev:/
>
> */
> /*
>
> */indev: /*The device name where you mounted the PDP–11 C
> distribution medium.
>
> */
> /*
>
> */outdev: /*The installation device name (the device where you wish
> to install PDP–11
>
> C). If you desire a standard installation of PDP–11 C, specify *SY:
> *as the

>
> installation device.
>
>
> So, assuming you are using the TM11: backup/restore/sys mt0:pdp11c/
> saveset,*.* SY:
>
> Good luck,
> Clem
>
> On Mon, May 18, 2026 at 5:14 PM isy...@gmail.com

> <mailto:isy...@gmail.com> <isy...@gmail.com <mailto:isy...@gmail.com>>

> wrote:
>
> Excellent! I would note that I am not quite sure where DEC's
> definitive RT11 c compiler is. There are various links to
> the original K&R code about the place but I have not seen it all put
> together for RT11. The nearest I have is
> in the UNIX builds and I think the best/stable (???) version is in
> the last version of Ultrix for the PDP11 ... V3.x.
> If you make any progress here, do let us all know.
>
> BW, Ian
>

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[isy...@gmail.com]

Hi Clem,

 Thanks for your very useful homework. Just checked a volume named rt11c.dsk (RL01) from the layered products directory.

 The cc compiler runs but I haven't tried any tests as yet.  There is a doc file titled: PDP-11 C V1.2 (RT-11) RELEASE NOTES.

 I would also note that the doc refers to RSX/TSX/RSTS and there are .OLB library files on the disk. I wonder if cross

 OS compiles are supported ... looks very likely for RSTS/E.  In addition, the doc file confirms ANSI compliance ... C89.

 All in all, this looks like a very useable environment for c development under RT11(XM).

Regards, Ian.

[Johnny Billquist]

Just a short other comment on something I only spotted now.

Clem's suggestion of DT (DECtape) for the image is just crazy wrong.
DECtapes are not magtapes, and this whole description does not work at
all if you try with that. DECtapes are like disks.

And I don't know, but did people miss that I posted a link to the
trailing-edge site with the PDP-11 C compiler earlier? Seems like some
people don't see (or read) when I write something...

Johnny

On 5/19/26 04:57, Clem Cole wrote:
> Answering a few questions WRT the official compiler vs the DECUS C
> compiler, please note that I previously answered that the DECUS compiler

> will work on a traditional RT-11 system (/a.k.a/., RT-11/SJ or RT-11/

> FB).  But the OP did ask about the official layered product, as did Ian;
> I'll offer a more complete answer.  It's a bit more complicated.
>
> Also, I note that the target system for the DEC layered product (PDP-11
> C) requires a PDP-11 with an MMU and running what DEC called RT-11/XM
> with at least 256K of memory.  I'm going to assume you have sysgen'ed an
> RT-11/XM and set up OpenSIMH for a PDP-11 with an MMU.
>

> Before I got further, https://web.archive.org/web/20220928104818/http://
> mim.stupi.net/manuals/LAYERED/ <https://web.archive.org/

> web/20220928104818/http://mim.stupi.net/manuals/LAYERED/> has four files:
>
> PDP-11 C V1.2
>

> * AV-NA47D-TC Cover Letter [pdp11c1.pdf]
> * AA-NA46D-TC Installation Guide [pdp11c2.pdf]

> * ??? Guide to PDP-11 C [pdp11c2.pdf] - I believe this is some
> version AV-NA45x-TC
> * ??? PDP-11 C RTL Reference Manual [pdp11c2.pdf] - I believe

> this some version AV-NA45x-TC
>
> Unfortunately, the 4th file is corrupt (and seems to have been that way
> for several years, it seems), and I have not found a copy AV-NA45x-TC
> [the RSTS Guide to documentation lists it as AV-NA45A-TC]
>
> The directory https://ftp.trailing-edge.com/pub/rt_dists/layered/
> <https://ftp.trailing-edge.com/pub/rt_dists/layered/> is believed to

> containmany of the DEC layered products. including: rt11_c_v1_1.zip,

> which is a zipped file of a virtual tape rt11_c_v1_1.tpc
>

> Given that this is a tpcformat file, I will wager that it's either a

> copy of the 9-track image or the TK50.
>

> The good news is that OpenSIMH can understand all of TAP, TPC,E11or

> P7B virtual tape formats. Youcan also use either the older mtcvtv23(1)
> or the newer tpc2mt(1)  tools to create a nativeTAPformat file.

>
>
> If you leave it as TPC format, the command to sim>attach -r -F TPC <YOUR
> TAPE DEVICE>  rt11_c_v1_1.tpc will mount the tape (readonly). If you

> convert to TAPfirst, the -F TPCis not needed.  Either way, you need to

> replace<YOUR TAPE DEVICE>with one of:
>

> * MS0 for a TS11/TS05 using the RT11MS.SYS device driver and OpenSIMH
> TS device.
> * MU0 for a TK50/TU81 using the RT11 MU.SYS device driver and OpenSIMH
> TQ device.
> * MT0 for a TM11/TU10 using the RT11 MT.SYS device driver and OpenSIMH
> TM device.
> * DT0 for a DECtape using the RT11 DT.SYS device driver and OpenSIMH

> TC device.
>
> What I cannot tell you for sure, because I have not investigated/tied it
> myself, is the format the RT11 is expecting.   But if you look at the
> second file listed above (AA-NA46D-TC Installation Guide [pdp11c2.pdf])

> started on Page 6-1  — *Chapter 6 - **Installing PDP–11 C on a RT–11
> Operating System *

>
> According to that page, DEC released PDP-11 C on one of an RL11, a1600
> BPI 9-track, a TK50, 6 RX50 diskettes, or 10 RX01 diskettes.
>
> Assuming you have booted RT-11/XM, make sure you have a tape configured

> in openSIMH, and a tape device driveris loaded.   Todo that type: show

> devicesto list all devices currently installed and configured in the
> operating system's device table. Look for your device prefix (/e.g./,
> MS, MU, MT, DT in the left-hand column).  Thentype: show subto list the

> currently loaded subsystem table, identifying which drivers are actively
> resident in memory or available for system execution.  If you don't see

> one, then type: installxxwhere xxis one of MS, MU, MT, or DT

>
> Moving to page 6-4 and assuming this is a tape image:

> *
> *
> *6.2.2 Installing from Tape*
>

> To install PDP–11 C from a 1600 bpi magtape kit or TK50 tape
> cartridge, place
>
> the PDP–11 C distribution medium in the drive and then issue the
> following
>
> DCL command:
>

> backup/restore/sys /indev:/pdp11c/saveset,*.* /outdev:/
>
> */
> /*
>

> */indev: /*The device name where you mounted the PDP–11 C
> distribution medium.
>
> */
> /*
>
> */outdev: /*The installation device name (the device where you wish
> to install PDP–11
>
> C). If you desire a standard installation of PDP–11 C, specify *SY:
> *as the

>
> installation device.
>
>
> So, assuming you are using the TM11: backup/restore/sys mt0:pdp11c/
> saveset,*.* SY:
>
> Good luck,
> Clem
>
> On Mon, May 18, 2026 at 5:14 PM isy...@gmail.com

> <mailto:isy...@gmail.com> <isy...@gmail.com <mailto:isy...@gmail.com>>

> wrote:
>
> Excellent! I would note that I am not quite sure where DEC's
> definitive RT11 c compiler is. There are various links to
> the original K&R code about the place but I have not seen it all put
> together for RT11. The nearest I have is
> in the UNIX builds and I think the best/stable (???) version is in
> the last version of Ultrix for the PDP11 ... V3.x.
> If you make any progress here, do let us all know.
>
> BW, Ian
>

> --
> You received this message because you are subscribed to the Google
> Groups "[PiDP-11]" group.
> To unsubscribe from this group and stop receiving emails from it, send
> an email to pidp-11+u...@googlegroups.com
> <mailto:pidp-11+u...@googlegroups.com>.
> To view this discussion visit https://groups.google.com/d/msgid/pidp-11/

[Clem Cole]

below

On Tue, May 19, 2026 at 5:47 AM isy...@gmail.com <isy...@gmail.com> wrote:

Hi Clem,

 Thanks for your very useful homework. Just checked a volume named rt11c.dsk (RL01) from the layered products directory.

I suspect that is from: https://pdp-11.org.ru/~form/files/pdp-11/rt-11/layered/

Do you have any idea if it is a raw DEC install disk or something that has been installed?  The index says all the files have been patched.

How does it compare to what is described in AA-NA46x-TC C Installation Guide? 

 The cc compiler runs but I haven't tried any tests as yet. 

fair enough. 

There is a doc file titled: PDP-11 C V1.2 (RT-11) RELEASE NOTES.

If we go by the file name:  https://ftp.trailing-edge.com/pub/rt_dists/layered/rt11_c_v1_1.zip

The version you found is newer and possibly Y2K patched.  It also matches the docs I found in the Wayback Machine.

 I would also note that the doc refers to RSX/TSX/RSTS and there are .OLB library files on the disk. I wonder if cross

 OS compiles are supported ... looks very likely for RSTS/E. 

I believe that it is supposed to. Remember, this compiler was originally released for VMS.  As the SPD for the original VAX product says:

The compiler runs in native mode, as a cross compiler, on the host VMS environment and produces PDP–11 object code compatible with all the supported target systems. These target systems are RSX–11M, RSX–11S, RSX–11M–PLUS, Micro/RSX, RSTS/E, RT–11, and VAX–11 RSX. The Run-Time Library is provided in object form.

Reading the "Cover Letter" DEC document: AV-NA47D-TC The Description says:

PDP-11 C, Version 1.2 is a C language processor for Digital's major operating systems on the PDP-11. The language processor is hosted native on VAX/VMS, RSX-11M-PLUS, RSX-11M, Micro/RSX, RSTS/E, and RT-11. Target systems are RSX-11M-PLUS, RSX-11M, RSX-11S, Micro/RSX, RSTS/E, RT-11 and VAX-11 RSX. PDP-11 C is highly compatible with the ANSI Standard for the C language.

As the SPD for the SPD for the RT-11 product says:

The compiler runs in native mode on the RT–11 mapped host systems and produces PDP–11 object code compatible for all the supported target systems.  These target systems are RSX–11M, RSX–11S, RSX-11M–PLUS, Micro/RSX, RSTS/E, RT–11 (both mapped and unmapped monitors), and VAX–11 RSX. The Run-Time Library is provided in object form.

The SPDs were used to determine what the product is said to support (note that at DEC, we had a notion of 'latent support' - which are features that engineering may have done, but are not officially recognized as part of the product). This URL has a fairly complete list and pointers to many of them [although there are dead links]:

http://zx.net.nz/mirror/h18000.www1.hp.com/info/SPD/

The two general SPDs that are for RT-11:

12.01  RT-11, Version 5.7 (Single-User Operating System)                                             29 Oct 1998

http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP1201/SP1201PF.PDF

20.96

RT-11 Optional Software Cross Reference Table                                                             21 Sep 1992

http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP2096/SP2096PF.PDF 

The PDP-11 C Compiler SPD's are:

31.54   PDP-11 C FOR VMS, Version 1.2                                                                           28 Jan 1992

http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP3154/SP3154PF.PDF

09.30   PDP-11 C for RSX-11M and RSX-11M-PLUS, Version 1.2                                    29 Mar 1995

http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP0931/SP0931PF.PDF

09.31   PDP-11 Micro/RSX PDP-11C, Version 1.2                                                             29 Mar 1995

http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP0931/SP0931PF.PDF

09.32   PDP-11 C for RSTS/E, Version 1.2                                                                        29 Mar 1995

http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP0931/SP0931PF.PDF

09.33   PDP-11 C for RT-11, Version 1.2                                                                            29 Mar 1995

http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP0931/SP0931PF.PDF

[Clem Cole]

As an FYI: I noted a discrepancy between the Installation guide [DEC doc # AA-NA46D-TC] and the product's SPD [09.33.03], which possibly could be important. The SPD says the product is distributed on 9-track and TK50 only, while Page 6-1 of the installation guide suggests that an RL02, RX50, or RX01 media is possible.  I bring this up because you mentioned you found an RL image of the product.  Both reference Version 1.2, but the installation guide [AA-NA46D-TC] is dated February 1992, while the SPD was published on 29-Mar-95.  This makes me wonder about the bits you found.  There are numerous ways these two documents can be out of sync, but the SPD is the formal definition for customers of what the product does.  It is possible that Version 1.2 was delivered, the TLG (Technical Languages Group - the development team) folks created all 5 of the media kits, and at some point, DEC Product Marketing for Tech Languages dropped all but the two tape-oriented versions.   Another possibility is that the RL disk image you found is not an installation kit, but something someone other than the TLG development created at product release.

[Johnny Billquist]

There are no Y2K patches for the DEC PDP-11 C compiler. But it don't
have any Y2K problems to start with, as far as I know.
However, it will get into trouble in 2038. :-(

Johnny

On 2026-05-20 23:28, Clem Cole wrote:
> below
>
> On Tue, May 19, 2026 at 5:47 AM isy...@gmail.com

> <mailto:isy...@gmail.com> <isy...@gmail.com <mailto:isy...@gmail.com>>

> wrote:
>
> Hi Clem,
>
>  Thanks for your very useful homework. Just checked a volume named
> rt11c.dsk (RL01) from the layered products directory.
>
> Isuspect that is from: https://pdp-11.org.ru/~form/files/pdp-11/rt-11/

> layered/ <https://pdp-11.org.ru/~form/files/pdp-11/rt-11/layered/>

> Do you have any idea if it is a raw DEC install disk or something that
> has been installed?  The index says all the files have been patched.
> How does it compare to what is described in AA-NA46x-TC C Installation
> Guide?
>
>  The cc compiler runs but I haven't tried any tests as yet.
>
> fair enough.
>
> There is a doc file titled: PDP-11 C V1.2 (RT-11) RELEASE NOTES.
>
> If we go by the file name: https://ftp.trailing-edge.com/pub/rt_dists/

> layered/rt11_c_v1_1.zip <https://ftp.trailing-edge.com/pub/rt_dists/
> layered/rt11_c_v1_1.zip>

> The version you found is newer and possibly Y2K patched.  It also
> matches the docs I found in the Wayback Machine.
>
>
>  I would also note that the doc refers to RSX/TSX/RSTS and there
> are .OLB library files on the disk. I wonder if cross
>  OS compiles are supported ... looks very likely for RSTS/E.
>
> I believe that it is supposed to. Remember, this compiler was originally
> released for VMS.  As the SPD for the original VAX product says:
>
> The compiler runs in native mode, as a cross compiler, on the host
> VMS environment and produces PDP–11 object code compatible with all
> the supported target systems. These target systems are RSX–11M, RSX–
> 11S, RSX–11M–PLUS, Micro/RSX, RSTS/E, RT–11, and VAX–11 RSX. The
> Run-Time Library is provided in object form.
>
> Reading the "Cover Letter" DEC document: AV-NA47D-TC The Description says:
>
> PDP-11 C, Version 1.2 is a C language processor for Digital's major
> operating systems on the PDP-11. The language processor is hosted

> nativeon VAX/VMS, RSX-11M-PLUS, RSX-11M, Micro/RSX, RSTS/E, and

> RT-11. Target systems are RSX-11M-PLUS, RSX-11M, RSX-11S, Micro/RSX,

> RSTS/E, RT-11 and VAX-11 RSX.PDP-11 C is highly compatible with the

> ANSI Standard for the C language.
>
> As the SPD for the SPD for the RT-11 product says:
>
> The compiler runs in native mode on the RT–11 mapped host systems
> and produces PDP–11 object code compatible for all the supported
> target systems.  These target systems are RSX–11M, RSX–11S, RSX-11M–
> PLUS, Micro/RSX, RSTS/E, RT–11 (both mapped and unmapped monitors),

> and VAX–11 RSX.The Run-Time Library is provided in object form.

>
>
>
> The SPDs were used to determine what the product is said to support
> (note that at DEC, we had a notion of 'latent support' - which are
> features that engineering may have done, but are not officially
> recognized as part of the product). This URL has a fairly complete list
> and pointers to many of them [although there are dead links]:
>

> http://zx.net.nz/mirror/h18000.www1.hp.com/info/SPD/ <http://
> zx.net.nz/mirror/h18000.www1.hp.com/info/SPD/>

>
>
> The two general SPDs that are for RT-11:
>

> 12.01*RT-11, Version 5.7 (Single-User Operating System)* 29 Oct 1998
>
> http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP1201/
> SP1201PF.PDF <http://zx.net.nz/mirror/h18000.www1.hp.com/info/
> SP1201/SP1201PF.PDF>
>
> 20.96
> RT-11 *Optional Software Cross Reference Table* 21 Sep 1992
>
> http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP2096/
> SP2096PF.PDF <http://zx.net.nz/mirror/h18000.www1.hp.com/info/
> SP2096/SP2096PF.PDF>

>
>
> The PDP-11 C Compiler SPD's are:
>

> 31.54 *PDP-11 C FOR VMS, Version 1.2 *28 Jan 1992
>
> http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP3154/
> SP3154PF.PDF <http://zx.net.nz/mirror/h18000.www1.hp.com/info/
> SP3154/SP3154PF.PDF>
>
> 09.30 *PDP-11 C for RSX-11M and RSX-11M-PLUS, Version 1.2*
>                       29**Mar 1995
>
> http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP0931/
> SP0931PF.PDF <http://zx.net.nz/mirror/h18000.www1.hp.com/info/
> SP0931/SP0931PF.PDF>
>
> 09.31 *PDP-11 Micro/RSX PDP-11C, Version 1.2*
>                                     29 Mar 1995
>
> http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP0931/
> SP0931PF.PDF <http://zx.net.nz/mirror/h18000.www1.hp.com/info/
> SP0931/SP0931PF.PDF>
>
> 09.32 *PDP-11 C for RSTS/E, Version 1.2*
>                                          29 Mar 1995
>
> http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP0931/
> SP0931PF.PDF <http://zx.net.nz/mirror/h18000.www1.hp.com/info/
> SP0931/SP0931PF.PDF>
>
> 09.33 *PDP-11 C for RT-11, Version 1.2 *
>                                              29 Mar 1995
>
> http://zx.net.nz/mirror/h18000.www1.hp.com/info/SP0931/
> SP0931PF.PDF <http://zx.net.nz/mirror/h18000.www1.hp.com/info/
> SP0931/SP0931PF.PDF>

>
>
>
> In addition, the doc file confirms ANSI compliance ... C89.
>  All in all, this looks like a very useable environment for c
> development under RT11(XM).
>
> Regards, Ian.
>

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> wwvKSnLS_4rtsskpcTJBfRm%3D%3DpAM-uJCyvXF6A%40mail.gmail.com?

[Neal G.]

Thanks for the tips everyone.

The comment, "Clem's suggestion of DT (DECtape) for the image is just crazy wrong." made me laugh.

I'd missed that information when I skimmed through Clem's response earlier.

But I don't think anyone would have thought the TPC file could be a Dectape image, the file is just too large. And my impression has always been that the TPC extension implies a 9-track tape image.

I've been successful in bringing up two RT11 PDP11-C  dev systems; one from the RL disk image and the other from the TPC tape image. Both pass the product installation tests (CCCIVP.COM) and are able to compile and run a few small math tests which I had initially created on RSX.

[Johnny Billquist]

Well, TPC format don't really imply 9-track, but it implies magtape, or
magtape-like media. Streaming tapes and all kind of other technology
also align with TPC. It's basically about any kind of media with
variable length records and tape marks.

Neither is true for DECtapes.

Johnny

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> groups.google.com/d/msgid/pidp-11/d5e61ee7-cd5e-4dbc-be88-
> dd1d525e84dan%40googlegroups.com?utm_medium=email&utm_source=footer>.

[Clem Cole]

On Mon, May 25, 2026 at 1:47 PM Neal G. <cven...@earthlink.net> wrote:

Thanks for the tips everyone.

The comment, "Clem's suggestion of DT (DECtape) for the image is just crazy wrong." made me laugh.

I'd missed that information when I skimmed through Clem's response earlier.

But I don't think anyone would have thought the TPC file could be a Dectape image, the file is just too large. And my impression has always been that the TPC extension implies a 9-track tape image.

Right.  Sorry if I confused some people.  Yes, I did include the TC11/TU56 in the list of tape subsystems supported by OpenSIMH and RT11, along with instructions on how to map OpenSIMH names to RT names and load the drivers (as intended). FWIW: I wrote the original message before I found the SPD for the product, which is the official statement of what the product is and how it is distributed. 

The error was adding the TC11/TU56 (RT-11's DT driver) to the line as an afterthought; I should have left the two tape schemes that OpenSIMH handles identically (9-track and TK50). While it is a tape system, OpenSIMH will not allow the same -F XXX switch to be attach comand for the TC device, as the virtual format for them is quite different. In fact, the attach command for the TC11 has instead -t (PDP-8 format), -f (18-bit format), or -a (autoselect).  Moreover, the "tape" blocks are fixed (578 bytes), and the tape metadata is quite different from that of a 9-track using the native TAP or earlier TPC formats (and we already knew this was TPC-formatted tape).  FWIW: Most people that I have worked with tend to use the 9-track emulations, because it works the same, no matter the OS or device manufacturer (ANSI standard can be helpful).  TK50 was a special thing that DEC created.  But it turns out that TK50's are able to be handled by the simulator identically to 9-tracks WRT to the virtual tape format.  The difference from the "on-tape" format is that 9-track tape records (using one of ANSI X3.22 - 800 bpi, X3.39 - 1600 bpi, or X3.54 - 6350 bpi) can range from 18 bytes to 65536 bytes per data record and are start/stop.  TK50s are always 512 bytes in a streaming scheme (but multiple can be read or written per operation, which is similar to how QIC-style tapes are recorded).  So as long as the "tape records" in the virtual tape are a multiple of 512 bytes, it works the same way; thus, TAP or TPC virtual tape files can be attached to either style tape controller.

I've been successful in bringing up two RT11 PDP11-C  dev systems; one from the RL disk image and the other from the TPC tape image. Both pass the product installation tests (CCCIVP.COM) and are able to compile and run a few small math tests which I had initially created on RSX.

Outstanding.   Glad it all worked out. 

Clem

[Johnny Billquist]

First of all, the DECtape on a PDP-11 have 512 byte blocks, not 578. And
the disk image is exactly those 512 bytes for each block. Just like any
other disk. There is no additional metadata of any kind. You can take a
DECtape image and attach it to an MSCP controller and vice versa, and
all will work fine (with the caveat that if you take an MSCP disk that
is of a different size than a DECtape is supposed to be, the additional
blocks will not be accessible).

The 18-bit systems have 578 bytes per block with DECtape, but simh
actually does 256 32-bit words in the disk image for those systems. But
only use 18 of those 32 bits. PDP-8 format DECtapes are a little more
complicated, but this is getting far from PDP-11 tapes now...


Second, the TK50 does not have 512 byte blocks. No idea where that came
from. It *might* be that internally the tape have some kind of fixed
format, but that is completely invisible (and in fact I don't think it
does, but if someone finds details on the actual on-tape format, that
would be nice). To any software, the TK50 looks no different than any
9-track tape drive, and is in fact programmed using the same TMSCP
protocol as the TU81 for example, and even use the same controller as
the TU81.

As such, it gives you variable length records, and tape marks. And
that's what any software have to deal with. And from the simh point of
view, this is what is needed to be emulated, which is why formats such
as TPC is used, and it is used for both traditional 9-track tapes and
compact tapes like the TK50. For simh, they are equivalent. And it's
exactly because simh needs to give records of variable length, so simh
needs to know the length of each record. And in addition, there are the
tape marks that also needs to be emulated.


And again, this is completely different than DECtape, which is just
another variant of a disk (even though it looks like a tape to a human
having one in the hand).

Johnny

On 2026-05-25 21:27, Clem Cole wrote:
>
>
> On Mon, May 25, 2026 at 1:47 PM Neal G. <cven...@earthlink.net
> <mailto:cven...@earthlink.net>> wrote:
>
> Thanks for the tips everyone.
>
> The comment, "Clem's suggestion of DT (DECtape) for the image is
> just crazy wrong." made me laugh.
> I'd missed that information when I skimmed through Clem's response
> earlier.
> But I don't think anyone would have thought the TPC file could be a
> Dectape image, the file is just too large. And my impression has
> always been that the TPC extension implies a 9-track tape image.
>
> Right.  Sorry if I confused some people.  Yes, I did include the TC11/
> TU56 in the list of tape subsystems supported by OpenSIMH and RT11,
> along with instructions on how to map OpenSIMH names to RT names and

> load the drivers (as intended).FWIW: I wrote the original message before

> I found the SPD for the product, which is the official statement of what
> the product is and how it is distributed.
>

> The error was adding the TC11/TU56(RT-11's DT driver) to the line as an

> afterthought; I should have left the two tape schemes that OpenSIMH
> handles identically (9-track and TK50). While it is a tape system,

> OpenSIMH will not allow the same -FXXX switch to be attach comand for
> the TCdevice, as the virtualformat for them is quite different. In fact,
> the attach command for the TC11 has instead -t(PDP-8 format), -f (18-bit

> format), or -a (autoselect).  Moreover, the "tape" blocks are fixed (578
> bytes), and the tape metadata is quite different from that of a 9-track

> using the native TAPor earlier TPCformats (and we already knew this was

> TPC-formatted tape).  FWIW: Most people that I have worked with tend to
> use the 9-track emulations, because it works the same, no matter the OS
> or device manufacturer (ANSI standard can be helpful).  TK50 was a
> special thing that DEC created. But it turns out that TK50's are able to

> be handled by the simulator identically to 9-tracksWRT to the virtual

> tape format.  The difference from the "on-tape" format is that 9-track
> tape records (using one of ANSI X3.22 - 800 bpi, X3.39 - 1600 bpi, or
> X3.54 - 6350 bpi) can range from 18 bytes to 65536 bytes per data record
> and are start/stop.  TK50s are always 512 bytes in a streaming scheme
> (but multiple can be read or written per operation, which is similar to
> how QIC-style tapes are recorded).  So as long as the "tape records" in
> the virtual tape are a multiple of 512 bytes, it works the same way;
> thus, TAP or TPC virtual tape files can be attached to either style tape
> controller.
>
>
>
> I've been successful in bringing up two RT11 PDP11-C  dev systems;
> one from the RL disk image and the other from the TPC tape image.

> Both pass the product installation tests (CCCIVP.COM <http://
> CCCIVP.COM>) and are able to compile and run a few small math tests

> which I had initially created on RSX.
>
> Outstanding. Glad it all worked out.
> Clem
>

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