5. PDP-11/23 SE ( Special Edition )


The system was built up almost exclusively with DEC standard components though with following 4 exceptions or unusual features:
1) Chasis is do-it-yourself
Q-BUS <--> CTI-BUS Converter is do-it-yourself
3) Original power supply was replaced by standard 300W PC power supply.
4) Additional hardware to provide the correct power-up sequenze , do-it-yourself
The Q-BUS <--> CTI-BUS Converter is controlling the 5MByte Hard-Disk which originally was from a DEC PC350 professional. Detailed information in chapter 5.1 .

5.1 Architecture

Emergence and Installation

The system was installed for the first time in 1983, in the beginning based on a KD11 processor board, also known as LSI-11/2 CPU ( M7270 ). As of 1985 to 1987 one PDP-11/23 CPU board (M8186) was used with the Floating-Point-Unit FPF11. End of 1985, an additional doubly floppy drive RX02 and a 5Mbyte RD50 Hard-Disk was installed. This Hard-Disk is attached to my own development, a Q-BUS <--> CTI-BUS Converter.

Further informations:

Detailed description of my PDP-11/23 SE, PDF document ( 15.942 KB )
Notice: Not translated yet ( I will do this if I have spare time in my spare time ).
Anyway, there are a lot of pictures included and all source code : RT-11 device driver, format program and disk-exerciser, written in MACRO-11 language. Source code: All explanations and comments in English.

circuit-diagram of my Q-BUS <--> CTI-BUS Converter , PDF document.

Video: via YOUTUBE.



5.2 Repairing + Restoration

Restoration of the System

The restoration of this system did start 2008 after approx. 22 years Cellar room storage, carried out in 2008. The damaged power supply ( uptime only 20 min ) was replaced by a standard 300W
PC power supply. There was only one problem, the PDP-11 requires a special power-up sequenze otherwise the PDP-11 would 't start. I designed a logic-board which includes the power-up logic and an additional 50Hz system clock generator ( see video ). The complete Outsides became by use of Plexi glass and LED changed to the effect, that an insight into the inside of the system is possible.



5.3 DEC Professional 350 ( PRO-350)


The DEC Professional 350 ( PRO-350) PC was developed in 1982 and was worldwide published as of 1985. The entry model was the PRO-325 system. This system only was equipped with a quad-density Floppy disk drive ( known as RX50 ). The PRO-350 system was equipped with a 5 or 10 Mbyte hard disk ( known as RD50/RD51) in addition. The development was done with an extremely big overhead of DEC first. It was one of the greatest challenge of DEC to become the Desk-Top market leader but this did not turn out well, though and unfortunately, it failed at long last. A very impressive VIDEO about the development of the PRO- 325 is provided from the COMPUTER-HISTORY museum. A technically detailed documentation is available here .

The operating system for the Professional 300 Serie was P/OS( Professional Operating System ), a modified version of RSX-11M with a menu-driven core user interface. Despite much internal criticism, the DEC marketing made up its mind to use the RSX-11M operating system as a basis for the P/OS. My opinion on it: It was the greatest erroneous decision in the company-history of DEC. RSX-11M was a Multiuser, Multitasking , Realtime operating system and not appropriated for the desk top environment. In my opinion were other systems been suitable much more better, like RT-11 with mit DIBOL and CIS ( Commercial Instruction Set ), RSTS or MUMBS. Result: The Professional 300 Series was not sold roughly in the desired quantities.



5.4 Structure


The Pro-350 in my collection is fully functional again. Some pictures to this:
Front view:

The DEC Professional 350 ( PRO-350) :

Opened system-unit cover:

The internal card cage had space for up to 6 options total:

RD50 , RD51 Disk controller:

RD51 Disk-Drive ( 10 Mb ) :

RX50 Floppy-Disk controller: