MSV11-K/L Jumpers
SLU Jumpers
Powerup Reset Circuit
UDC11 Jumpers




I have refurbished/built several small PDP-11/23's and sold or traded them, mostly on eBay. One purpose of this page is to serve as a useful reference for the people who now own these machines. Also, if you are interested in building your own PDP-11, this page might get you started.


Generally, each of these PDP-11/23's contains the following:

bulletKDF11-AA (M8186) CPU board, rev D, 22 bits. See Micronote 17 for info on this board, including jumper settings You can also use a KDJ11-A for a CPU in this rack. It's twice as fast, and it will run 2.11BSD if you can get a big enough hard drive..

bulletMSV11-L (M8059) 256K memory. Also MSV11-KP. The difference in the suffix on refers to the memory chips used. This board is briefly described in Appendix C of the "Micro/PDP-11 Handbook", 1983, and in more detail in "MSV11-L User Guide", EK-MSV0L-UG-001. I have summarized the jumpers here.

bulletAndromeda UDC11. This is an MSCP controller that handles a wide range of MFM hard drives and floppies. There is a utility program that runs under RT-11 that programs a non-volatile RAM on the board to remember the drive parameters. It can handle up to four physical drives and 8 logical drives. It can assign multiple logical DU's to a single hard drive. I have the manual and setup software for this board. Jumpers here.



SLU combo board. This board contains 2 DEC compatible serial ports, a somewhat non-standard LTC, and an undocumented parallel port. I believe it was built by 3M's Interactive Systems, which was purchased and absorbed by Allen-Bradley in 1986. Jumpers here.


bulletDLV11-J four port serial board. With the above boards, this is only good for RT11, unless you have an alternate source for LTC.

bullet5" floppy drive. The Tandon TM65-4 is compatible with RX50 disks (80 track, single sided), and also can handle 80 track, double sided disks that will hold 800K. The UDC11 setup software (OCT) calls it a TM100-4, which is the full height version.
bullet40 meg hard drive: Seagate ST251 or Mitsubishi MR535

This hardware will run 2.9BSD UNIX.

You can easily and cheaply build one of these from parts which are readily available. Here is a picture of a minimal and very inexpensive PDP-11 that will run 2.9BSD UNIX.

The hard drive is a Seagate ST151 (40 megs). Other hard drives that work are ST251, ST4096, and Maxtor XT1140. Other necessary items that are not shown in the picture are: power supply with +5 and +12, cooling fans, a terminal such as a VT420, and the terminal cable. VTserver can be used to load UNIX from a PC, once the hard drive has been set up and formatted.


This PDP-11 must be cooled with forced air. If the fans stop, the CPU and hard drive controller will overheat and fail. Two small fans blowing through the cage from the side works.

Certain hard drives, among them the DEC RD54/Maxtor XT2190, and the XT1140, also must be cooled with forced air. They overheat and start to get data errors in still air.

The card cage is an H9281-BA.

The small card on the back supplies power-on reset and other signals needed to make the CPU run. This is in lieu of a console with reset and run/halt switches. This card does not supply LTC, which is needed for UNIX and some versions of RT-11 Kermit. I'm not sure what the card is called or who made it. The card is described here.


Last modified: December 31, 2009