<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body><div>CP/M works a lot like this. But it's for 8989 not PDP11. It's also been ported to several other systems. Source code is available, but many folks don't consider it an OS.</div><div><br></div><div><br></div><div><br></div><div id="composer_signature"><div style="font-size:85%;color:#575757" dir="auto">Sent from my Galaxy Tab® A</div></div><div><br></div><div style="font-size:100%;color:#000000"><!-- originalMessage --><div>-------- Original message --------</div><div>From: Johnny Billquist <bqt@softjar.se> </div><div>Date: 10/22/16 7:11 PM (GMT-07:00) </div><div>To: simh@trailing-edge.com </div><div>Subject: Re: [Simh] RT-11 source </div><div><br></div></div>While we're at it then... Ray asked for RT-11, since he felt that it was <br>smaller and simpler than most other operating systems available, and <br>also because he felt more comfortable with assembler than some other <br>language.<br><br>Both those points are missed with any Unix-like OS, even if the <br>intention is good.<br><br>I could just as well offer up RSX, since it actually comes with source <br>where the comments are still in place, and it's actually written in <br>assembler for the most part as well. However, it is a much more complex <br>system than RT-11, and in some ways probably more complex than Unix as <br>well. So I don't think it might be a good choice if you just want to <br>understand how an OS works.<br><br>In fact, I would probably suggest Ray start with just writing some code <br>to do some simple things without looking at existing code. The first <br>thing needed would be to just have something that can load programs from <br>a device, and run them. This will require some simple device driver, <br>some simple file system, and a simple command line interpreter. Then you <br>can go on an expand from there. You'll soon realize things you want to <br>abstract away, and deal with in a somewhat coherent way.<br>I wouldn't bother with interrupt system, MMU, or any more fancy stuff to <br>start with. A plain 64K PDP-11, with the program loader just located in <br>one end, and then go from there. Do system calls through TRAP, EMT or <br>some other instruction, and then have a vector installed. If the user <br>program overwrites that, tough luck.<br><br> Johnny<br><br>On 2016-10-23 02:45, Nelson H. F. Beebe wrote:<br>> Ray Jewhurst <raywjewhurst@gmail.com> asks today for documented<br>> operating system source code for the PDP-11. Besides the Lions' Unix<br>> v6 code, there is also Doug Comer's Xinu project about which he wrote<br>> several books. Current versions are targeted at x86 and ARM CPUs,<br>><br>> http://www.xinu.cs.purdue.edu/<br>><br>> but he still provides code for older systems (PDP-11, SPARC, VAX):<br>><br>> ftp://ftp.cs.purdue.edu/pub/comer/<br>><br>> There is more about him here, including links to his books Web site:<br>><br>> https://en.wikipedia.org/wiki/Douglas_Comer<br>><br>> -------------------------------------------------------------------------------<br>> - Nelson H. F. Beebe Tel: +1 801 581 5254 -<br>> - University of Utah FAX: +1 801 581 4148 -<br>> - Department of Mathematics, 110 LCB Internet e-mail: beebe@math.utah.edu -<br>> - 155 S 1400 E RM 233 beebe@acm.org beebe@computer.org -<br>> - Salt Lake City, UT 84112-0090, USA URL: http://www.math.utah.edu/~beebe/ -<br>> -------------------------------------------------------------------------------<br>> _______________________________________________<br>> Simh mailing list<br>> Simh@trailing-edge.com<br>> http://mailman.trailing-edge.com/mailman/listinfo/simh<br>><br><br>-- <br>Johnny Billquist || "I'm on a bus<br> || on a psychedelic trip<br>email: bqt@softjar.se || Reading murder books<br>pdp is alive! || tryin' to stay hip" - B. Idol<br>_______________________________________________<br>Simh mailing list<br>Simh@trailing-edge.com<br>http://mailman.trailing-edge.com/mailman/listinfo/simh</body></html>