Back in the 1980s was my first introduction to computers. This was on a PDP-11/70 running RSTS/E V7.0 and a PDP-11/45 running UNIX V7. :Later the the 45 was upgraded to a 11/44 running 2.9BSD. Since cutting my teeth on these machines, I've always had a great fondness for the PDP-11 series.
PDP-11's were nice machines. Maybe not the fastest computers for their time, but their designs were typically simplistic and straight-forward in implementation. The instruction set is 16-bit with 8 general purpose registers, although R6 was used for the stack, and R7 the program counter. Some machine, like the 11/73, had separate instruction and data capabilities allowing a program to exceed 64KB to 128KB. Software overlays allowed a program to exceed 64KB of instructions, typically up to 512KB.
Back in January 2002, the Ebay bug hit me, and I discovered various DEC machines offered for auction there! My first machine acquired was a DEC PDP 11/23 clone from 3M circa 1984. This machine has 256KB of memory, and a ST-506 based disk. It currently runs 2.9BSD.
My next acquisition was a VAXStation 4000. Why? I always wanted a VAX to play with. ;-) Except, after the machine showed up I got distracted by other things going on in my life and put the e machine side for a while.
Okay, after that.. (yes.. I was hooked for a bit. ;-)) was a rack-mountable version of a Micro PDP-11/73. This came with two floppy drives, one ST-506 disk, and 1MB of RAM.
After that, a huge lot of DEC equipment appeared under one virtual electronic auction block. The lot contained 4 VAXStation 3100's, 1 InfoServer, 20 (yes twenty!) DECServer 200, 10 DECServer 300, 1 Microvax II, 1 DECServer 500, 1 DECMate system, and a sh*t load of DEC cables, serial connectors, and keyboards.. I won the block for ~$800 with an additional shipping of $600. Some of the equipment suffered damage during shipping with the MicroVAX II taking most of the dents. Thankfully, the machine still was able to NFS boot NetBSD 1.5.2 and the limited Linux VAX port.
The DECServer 200 and 300s are of not much important.. especially 30 of them. The machines talk DECNet and no TCP/IP. A bit of a bummer. It is possible use a DECNet package with Linux or FreeBSD to be able to log into the boxes, but it seems a little overkill. ALSO, they require boot images. Both boxes are integrated motherboards using Motorola 680X0 CPU's.
The DECServer 500 is of some major important. especially for PDP-11 hacking. This is a QBUS based system with a DEC Ethernet board, a PDP-11/55 processor board, and several serial QBUS cards. In short, its a small PDP-11 system without disks. Wanna build a PDP-11 system? Acquire a DECServer 500 and add MSCP QBUS card .. you might be able to run something on it.
I'm hoping to acquire a full cabinet PDP-11/70 with the front panel that has all the toggle switches and lights, and either a VAX-11/750 or VAX-11/780 at some point. I figure I'll stop then.. yep.. sure, trust me... I'm in control! Okay, well maybe or two more systems after that.
PDPs have been old for a while.So what do you do when the disks, which are no longer manufacture, start to fail? One solution is to use a MSCP emulation board. Dilog makes several Q-BUS emulation boards allowing a system to continue to run with SCSI drives. Yes, they still make them (as of July 2002), and yes they are very expensive. You may luck out and find one on Ebay.
I purchased a SQL-739 MSCP/SCSI board back in July 2002 from Dilog. This was an investment in getting the collection up and running.
The SQL-739 board is great. It can emulate several MSCP and TMSCP controllers using SCSI devices. Plug in a SCSI drive or 2 or 7, and suddenly the CPU can see a MSCP drive. There is ROM code that contains a menu based configuration to easily setup the board. Any SCSI drive can be dynamically mapped to a specific emulated MSCP controller.
The funny thing is an average modern SCSI hard disk can exceed the Q-BUS bandwidth (at 3.3MB) by several times. My high end Seagate drive in my desktop PowerMac does over 62MB/s throughput -- some 20X the speed of a double-wide Q-BUS.
It is possible to get a PDP on a Ethernet network running TCP/IP. To make this happen, you'll need the following items:
* 1 PDP CPU with Separate I&D
* A DEC Ethernet QBUS card
* A copy of the 2.11BSD installation
* Suggested 1MB of RAM
Okay, remember the micro PDP-11/73? Its running 2.11BSD and its on the net. Its slow, but usable! Telnet-ing into the box causes the load average to remain at a constant .5. FTP upload and downloads are around 35KB/s. Ping times are 33ms to another box on the same network, and 16ms to ping localhost.
The DEC Ethernet QBUS card came from the DECServer 500. The bus chases mounts are incompatible between the two boxes, but 2 minutes of drilling out the mounts corrected that problem. ;-)
Okay, so maybe you don't have any PDP-11 hardware. One of packages you can do this with is Bob Supnik's SIMH. Not does this package emulate a PDP-11, but it can emulate a PDP-1, PDP-8, PDP-10, PDP-18, and a VAX.
I used SIMH to create a networking 2.11BSD kernel. Okay, a 11/73 was fast for its day, but a simulated PDP-11/73 on PowerMac G4/1Ghz dual cpu machine running Mac OS/X with 62MB disk throughput is, obviously, faster. Building the entire kernel took less than 10 minutes under SIMH versus 1 hour on the 11/73. I created a disk image from the 11/73's drive by using a simple 'dd' command, then pointed SIMH at the image, built the kernel, then re-dump the disk image back to the drive, and connected it backup to the 11/73. And BINGO! the 11/73 booted with the image generated under SIMH.
http://www.pdp11.org is probably the best place to start, another good place is http://www.trailing-edge.com