PDP-11/03

You are either unaware of Multi-User Basic under RT-11 or you may have not remembered. While RT-11 has no file sharing capability and is certainly slow when run on a PDP-11/23 and limited in the size of files when only an RK05 is available, Multi-User Basic was available even before 1980 under RT-11. The Chicago Tribune required a system to handle their multi-million dollar newspaper printing presses. 11 computers had to be co-ordinated (using just 9600 baud serial lines - so there was a maximum of only 11 characters per millisecond and only very rarely was more than one computer active at a time) along with a data base that was kept of the 400 plates per day needed to print the newspaper. In 1981, the editorial offices were a few miles from the printing presses and sending a physical negative of each page was too time consuming. A microwave link was used to transmit the data for each page which then directly produced the physical plate for the press. The microwave signals had to be turned on within a time window of about 100 milliseconds, so the PDP-11/23 was quite adequate even when the signal had to be sent to 6 plate makers within that window. Multi-User Basic supported up to 4 users who entered the data as to which plates had to be made that day and which plates had been completed. It ran as a virtual background job under RT11XM. The foreground virtual job scheduled the 11 tasks controlling the 11 computers making the plates as well as the microwave switch. The foreground job scheduled each job on a round robin basis when there was any input character present to process and when finished gave the rest of the CPU time (probably over 95%) to Multi-User Basic. All this was done in 1981 with V04.00 of RT-11 with just 256 KB of physical memory. I don't know if it was ever upgraded to a PDP-11/73, but that would have been just a hardware upgrade. So while I agree that RT-11 is not often used in this manner, it can be done under the correct situation. In addition, while I agree that for a multi-user environment, scheduling a job based on its priority is essential, I have 6 VT100 terminals on my desk for the real PDP-11. System jobs are used to run 5 of the VT100 terminals in EDIT mode so that I can look at sufficient portions of the listing files which are produced by MACRO-11 along with having enough of the program listing displayed when I am debugging the program under SDX.SYS which freezes the complete system when stopped at a break point. While a bit inconvenient, it was not so difficult that switching to TSX-Plus was worth while to allow access to different parts of the listing as I progressed through the program. So, again, within a single user situation, RT-11 does easily support multiple jobs or multi-tasking, especially so under RT11XM with multi-terminal support. After I had set up this system, I stopped making hard copy listings of my programs and kept all of the current listings on a 600 MB ESDI hard drive. I have migrated the identical software to my PC and run Ersatz-11. The only difference is that the system runs many times faster than the PDP-11/83, the available disk space is many times larger, and there is only the single PC monitor on my desk with one keyboard - that is switched in less than 1/10 second supported by E11. In fact, it switches so fast that I can eyeball the different screens to detect where a listing changes to easily determine the differences (as long as the different copies of the same file are aligned, of course, with the same characters in the same location). I hope that my example of how I use RT-11 has convinced you that RT-11 (within the limitations due to the scheduling algorithm) is just as much of a "multitasking/timesharing" system as RSX-11 and RSTS/E. I often set the background task to execute a command file which assembles and links the current program beng developed WHILE I use the system EDIT jobs to look at the listing of the program, especially when the program has many subroutines and many assemblies combined into one program at the end. Jerome Fine