SimH

Parallel to the physical PDP-11/70, here is a simulated version of it. It is photorealistic, written in platform-independent Java and connects to a modified SimH over network.This SimH contains an extended PDP-11/70 CPU and logic to interface to the Java panel. So the simulated 11/70 can be controlled over the panel in a realistic way, and also displays the history correct light patterns.Per default SimH executes RSX11-M. And yes: the famous "idle pattern" of RSX11M now appears on your desktop! (Like in this video of a real 11/70) For the simulation I shot lots of photos from the real panel, then processed them with Photoshop. It is the same processing chain as described for the PDP-10 KI10 panel.This PDP-11/70 panel simulation is very similar to the PDP-11/40 panel I made before. So this description page is essentially a link page to the 11/40 Blinkenbone project.Download and installDownload is from GitHub, see here for detailed info.To install, just unzip into an arbitray directory and execute the "pdp1170.bat" (or ".sh") batch file.What's running?After start, two separate applications run on your desktop: SimH and the panel simulation.Both communicate over a network protocoll, so perhaps your firewall will ask wether some ports should be opened. Agree!SimH executes a RSX11-M distribution, so you should be familiar with that OS. A basic PDF doc about RSX11-M is included in the archive. You operate the running PDP-11/70 through SimH's console terminal window as usual. Of course you can run any disk image on SimH by modifiying the "ini"-file.The modified SimH implemenets an additional "REALCONS" device to control the panel, see here for details.And the RSX11-M distribution was prepared by Mark Matlock, check out his article about RSX11M on SimH. He too connected a (blue!) PDP-11/70 panel to SimH with BlinkenBone, watch his video.Operating the panelAgain, this is just a quick guide! The PDP-11/40 page contains more instructions and a little MACRO11 program, which shows a running light on the panel if keyed in correctly.You operate the Java panel by just clicking onto the switches and the two knobs.For a lamp test, click the unlabeled white switch.To stop the simulation, press switch HALT. You'll notice that SimH goes to it's console mode, the simulation is stopped. To restart, release HALT and click CONT.You can also single step through the RSX11-M code by pressing CONT while HALT is active. SimH will show the current opcode.To manipulate memory, use the

Systems, but we can communicate and transferdata to and from them using modern technologies and protocols. A greatdeal of thanks is owed to the contributors of SIMH. Their decision tocontribute and release under open source furthers all our understandingof our history and guarantees that this history will always be free.Getting Started: Installing SIMHDownload the latest SIMH release, V3.4-0 at the time of this writing,compile and install. If you want to use Ethernet emulation, you may needto upgrade the libpcap library bundled with your OS as most currentlydistributed versions are too old. The SIMH installation documents explainhow to do this, and you can skip this step if you're not going to be usingnetworking support on your simulated machines. Compiling can be doneas any user and is as simple as:$ mkdir simh$ cd simh$ unzip /path/to/simhv34-0.zip$ mkdir BIN # Note all CAPS$ gmake USE_NETWORK=1 all# Only include USE_NETWORK=1 if your PCAP lib is up to date.(compilation chatter omitted)$ ls -l ./BIN/total 11624-rwxrwxr-x 1 matt matt 301959 Jul 16 18:45 altair-rwxrwxr-x 1 matt matt 482274 Jul 16 18:45 altairz80-rwxrwxr-x 1 matt matt 529317 Jul 16 18:44 eclipse-rwxrwxr-x 1 matt matt 297590 Jul 16 18:45 gri-rwxrwxr-x 1 matt matt 375737 Jul 16 18:44 h316-rwxrwxr-x 1 matt matt 577678 Jul 16 18:44 hp2100-rwxrwxr-x 1 matt matt 355225 Jul 16 18:44 i1401-rwxrwxr-x 1 matt matt 381672 Jul 16 18:45 i1620-rwxrwxr-x 1 matt matt 441079 Jul 16 18:46 ibm1130-rwxrwxr-x 1 matt matt 502037 Jul 16 18:46 id16-rwxrwxr-x 1 matt matt 508378 Jul 16 18:46 id32-rwxrwxr-x 1 matt matt 294614 Jul 16 18:46 lgp-rwxrwxr-x 1 matt matt 434940 Jul 16 18:44 nova-rwxrwxr-x 1 matt matt 345034 Jul 16 18:41 pdp1-rwxrwxr-x 1 matt matt 752055 Jul 16 18:43 pdp10-rwxrwxr-x 1 matt matt 1055376 Jul 16 18:43 pdp11-rwxrwxr-x 1 matt matt 474153 Jul 16 18:42 pdp15-rwxrwxr-x 1 matt matt 459203 Jul 16 18:41 pdp4-rwxrwxr-x 1 matt matt 460363 Jul 16 18:41 pdp7-rwxrwxr-x 1 matt matt 499473 Jul 16 18:42 pdp8-rwxrwxr-x 1 matt matt 467662 Jul 16 18:42 pdp9-rwxrwxr-x 1 matt matt 352233 Jul 16 18:45 s3-rwxrwxr-x 1 matt matt 429312 Jul 16 18:46 sds-rwxrwxr-x 1 matt matt 982694 Jul 16 18:43 vaxThis builds all possible system simulators. Each simulator becomesa separate binary in the ./BIN/ directory. SIMH can be run as anynormal user, but if you want to use Ethernet network simulation, youneed to execute it as root (under UNIX) to allow libpcap access to theEthernet device.Running UNIX V5UNIX V5, released in June 1974, was still very early in UNIXdevelopment at Bell Labs. Much of the system was still writtenin assembler. This disk image includes a working C compiler (cc)and a great deal of interesting source code under /usr/source.To begin our exploration, we must download the UNIX V5 disk image (seeResources). This zip archive containsthe pre-installed image file as well as a README and file containinglicense information. The disk image is a snapshot of a working installedsystem. In this case, it is simulating an RK05 disk drive. We must nowcollect the pieces we need to get this system booted. Begin

I have been called “nostalgic beyond my years” by some, and I supposethat is accurate. I was born in 1976 and have always had a voraciousappetite for early minicomputer and mainframe history. I believerecorded history itself is the single-most important innovation of humanexistence. We humans seem to have a hard-wired compulsion to record,pass on and learn from the mistakes and successes of those before us.Open-source software is the natural evolution of this concept appliedto computer technology. In the Open Source philosophy, we are allfree to learn from the wealth of software created by the masses thatcame before us. By examining the evolution of a project, we can learnfrom the mistakes of others and, perhaps most important, copy verbatim fromtheir successes. By harnessing this freely available history as wellas unfettered cooperation, we advance the common good.Recently, companies have begun to loosen their grip on their earlycomputing “intellectual property”. Although some have not fully embracedopen source, these sometimes small, token gestures offer us a wealthof knowledge. In this article, I focus on how wecan explore early operating system history by running“historic” UNIXreleases on our very own Linux boxes using a simulator. The SCO Group(Yes, “them”, previously Caldera, Inc.) claims current ownership of earlyUNIXes and has released them under an “Ancient Unix”license, which allowsfor noncommercial use. I focus here on the UNIX V5 release, because itis the earliest available. UNIX V6, V7 and various early BSD releasesare also available. If you plan on trying out any of these OSes,examine the licenses included with each before booting them up.Stranger in a Strange Land: the UNIX V5 User EnvironmentThe UNIX V5 system provided in the disk image is rather stark andunfriendly compared to modern, lush UNIX/Linux systems. Here are a few pointers toget you started:sh is the shell. It's only 858 lines of C; don't expect it to worklike bash.Use chdir to change the default directory.Backspace and arrow keys rarely work.ed is the text editor; see en.wikipedia.org/wiki/Ed.bas is a basic interpreter.fc is a FORTRAN interpreter.cc is the C compiler.Source code is in /usr/source.There are not many files, so use find / -print tosee what else is included.In order to explore these OSes, we need to be able to run them oncommonly available computing hardware. Luckily, we have simulatorsfor this purpose. Because of its quality and depth of support,one of the most popular simulators is SIMH, available fromthe SIMH Web site (see the on-line Resources). SIMH runs on every popular*nix OS, aswell as Microsoft Windows, and is capable of simulating a wide range ofearly computer systems, including Digital Equipment Corp.'s PDP and VAXsystems, the MITS Altair, early IBM systems and many more. Some ofthe most historically significant systems are DEC's PDP series, thebirth-system of UNIX.SIMH is a ground-up system simulator; it simulates the CPU, memory,firmware and devices of a number of early computer systems. Thismeans that original distributed software can run unmodified on thesesimulated systems. SIMH successfully simulates devices such as disks,tape drives, printers and networking devices. This means that not onlycan we run these historic

Let's pretend for a moment you are as crazy as myself about computing and, specially, about classic computers like the PDP-11. Let's say your crazyness gets to the point you start to consider seriously writing your own operating system for the PDP-11. Or, at least, doing the first steps to write something similat to an operating system. Sounds scary, doesn't it? No way! It sounds fun!Still reading? Fine, because we are going to do those very first steps towards this goal. And the very first step to build an operating system is to have the hability to write, debug and run standalone software. That is, to run programs in a PDP-11 without any operating system loaded.To do that, we can use two different approaches:We can use a running PDP11 system with an existen operating system to write and assemble the software, moving it to our "empty" system.We can use a cross-assembler and cross-compiler to write the software under another operating system, and feed it to our PDP11.At this point, it is important to remember we are talking about a simulated PDP-11. At least in my case, I don't have access to a real machine. Then, it makes sense to use the host operating environment to write and compile the software we will run in the simulator. The plan is to be able to build files loadable into the SIMH simulator using the "load" console command. Then we can use simh to run the software or to single step it. No operating system needed for that.Load file formatSimh can load into memory files representing a paper tape image. Yup, you have read it well. Punched paper tape. Now we are talking about classic computing! We can find the format of those images reading the pdp11_sys.c source file of the simh distribution. The code is in a function called sim_load. The comments block of that function describes the file format, which is not very complicated. The file is composed by byte blocks, each one of them preceded by a header and followed by a checksum. The last block is en empty one (just header and checksum). The structure of the header is as follows: Offset Length Datatype Content 0 1 char Fixed value: 1 1 1 char Fixed value: 0 2 2 word Size of the data block, in little endian format 4 2 word Load address for that block, in little endian formatThe checksum is computed adding every byte value of the block including the header and taking the 2's complement of the low order byte of the result. In other words, the negative value of the low order byte taken as an unsigned character.The last (empty) block also contains a

"load address", but in this case the content of that field will be loaded into the PC register of the machine after the file has been loaded. So it has to contain the entry point for the loaded program. We will refer to this format as "load format".Generating a load format fileFrom RT-11The easiest way to generate a load file is to use a running RT-11 system. The RT-11 linker has the option of generating directly load files instead of native executables. We have just to add the "/LDA" switch to the LINK command and we'll get a file with a LDA extension instead of the usual SAV one. The linker will set up the file to load at the octal address 01000 by default, just over the interrupt vector area, so we will be mostly fine with the default. We can change it using the /BOTTOM switch if we really need to load our code in any other place.So, we can edit our source code in our RT-11 system, assemble/compile it using the native MACRO-11 compiler or whatever HL language we want, and LINK the resulting object into a LDA file. Now we have to transfer that file to our host environment. We have several options to do that. As examples:We can use KERMIT to move the file to our host system. For some reason, I've not been able to do this. When I launch KERMIT in SERVER mode in the RT-SYSTEM it ignores my download requests. We could use a TCP/IP stack. I haven't done that, so I can't really help about that option.We can use the paper tape emulation in SIMH. To do so, we have to SYSGEN our RT-11 adding the PC device, and then we can simply COPY from or to PC: to transfer the files.This procedure works, but you have to use the RT-11 environment and specifically the KED editor, which I've found difficult to use with my terminal emulators. You can edit in your host environment and use the paper tape device to upload your sources to RT-11, but its quite cumbersome (and you must be sure you are using the DOS convention for the line terminators...), so I wanted to find an alternative.Cross-compiling and cross-assemblingThe obvious solution is to use a cross-assembler and a cross-compiler to generate the PDP-11 code directly in your host environment. In my case, that host environment is a laptop running Ubuntu Linux. After asking in the simh mailing list, I found myself with several opti (ons:The simh distribution contains a port of the "native" assembler, MACRO-11, to unix. It compiles without problems and generates PDP-11 object files. It also uses the DEC source format (being a port