Ignoring the fact that even a 4 card PDP-11 Qbus system has a large physical footprint when one throws in the power supply, they are beautiful systems to create standalone systems with. If one has a parallel port and realtime clock, then one can replace a huge number of dedicated control circuits which have purely digital inputs and outputs. The reason that I like the PDP-11 so much is that when it powers on, it starts executing in console mode which is a monitor program that allows one to either boot various physical devices, or to load/examine data in various memory locations. Simple programs can be entered as a series of octal numbers via a dumb terminal, or one can boot the system from the parallel port. I used this approach when I used a PDP-11/23 as a data acquisition system for a PDP-11/44, and all I had to do was to enter parallel port bootstrap code via console, and the PDP-11/23 would then load my minimalist OS via parallel port which then allowed the machine to load and execute my data acquisition program. For those who have an interest in the PDP-11/23, here are some photos of a few boards. For more information about PDP-11's, repositories of PDP-11 code, etc go to http://www.trailing-edge.com/.

The ability to set/examine any address via a serial connection is immensely usefull and no other computer system has ever used this interface again to the best of my knowledge (I'm not including various microcontroller systems which can be programmed via a serial port; they are not as easily obtained as the ubiquitous IBM PC). One thing I had considered was to use IBM PC clones for microcontrollers as I have picked up 80386SX motherboards for under $5 and SIMM's now are on the order of $1/megabyte. Throwing in an equally cheap video card and parallel port/serial port card gives one processing power that is theoretically far greater than the PDP-11/23 system I've discussed, but when one powers up this system, nothing happens. Well, I shouldn't say that nothing happens, various messages flash on the screen of ones monitor and usually the system hangs with some type of error message that there is no boot disk.

If anyone knows where I can get a BIOS that allows use of a serial port as the boot device, I would be very interested. I could disassemble the BIOS for a particular machine and determine where the boot code is entered and replace it with a simple monitor program like on the PDP-11; unfortunately my tmie is now worth enough that I would be better off buying a complete computer system than spending a few hours trying to come up with this serial BIOS. One does not need a hard disk drive or floppy drive to run simple controller applications. Code for such applications might be 1 Kbyte if they are especially complicated and this takes almost no time to squirt through a serial connection to the monitor program.

The obvious question people will ask me at this point is why don't I get a microcontroller like the Basic Stamp or similar device? There is nothing wrong with these devices, except most of my applications require considerbly more processing power than the Basic Stamp can bring to bear.