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Many years ago, my high school had a VAX (not sure what model, but from the size I remember, it easily could have been an 11/750!) running VMS which ran the administrative functions of the school as well as some other mundane things, such as the library's card catalog system. During my sophomore year of high school, I found this out, and found a simple loophole that let me log in and get a normal shell, as opposed to the menu system that I was "supposed" to be using. Apparently, some administrators at my high school didn't like me being able to "play" on their VAX with SYSTEM privileges, so I got a short suspension after my parents and others plead with the administrators that I shouldn't get tossed out for a couple of weeks because of it. That was the only time I ever got "disciplined" while I was in high school.
I must admit, it was sort of fun looking around, it was the first time I had access to a "real" computer (something that wasn't a PC or a Mac of some sort). Before you start accusing me - no I didn't do anything malicious to the system, and I didn't even find out where the thing kept grades. VMS has some strange file-system layout possibilities, and I didn't know much (anything) about VMS at the time other than what I found in a "hacking guide" which turns out to be actually a fairly good resource for learning some basic VMS.
Now, on to the interesting stuff...
Well, it turns out that my 11/750 wanted to be elusive - a broken fuel pump thwarted my first attempt to pick it up, and when I tried getting it shipped, the driver of the truck delivered it to the wrong place. But, I eventually got it here to my shared office.
Next, I opened it up, and looked inside. The picture below is of it powered on, but be assured that the machine didn't actually get powered on until much later. After all, I had to check out the hardware and make sure there wasn't something metal sitting in it that was going to short out the power supply on accident!
The first thing I did was to look over the configuration - see what cards I really had, what slots they went into, etc. I checked that all of the empty slots had grant continuity cards in them. My machine seems to use "knuckle buster" short grant cards, and wire-wraps the remaining lines on the backplane. I noticed that the memory controller card (L0016) was stuck in the wrong slot of the backplane (why? Maybe someone pulled it out and didn't know where it went?).
After fixing that, I prayed that the power consumption was less than the label on the back indicated (other peoples' web sites on 11/750s seem to claim a lower power consumption than what the label on it does), and wired up a 30A to 15A (120V AC) converter cable, and plugged it into a spare 20A circuit. After running for 10-15 minutes, the cables were still cool, and the plug was just barely warm to the touch (it was colder than the plugs on the power strips from our clusters, which push about 16A through a 20A plug). I'm going to guess that it uses about 12A at 120V AC, which is 1/2 of the 24A rating stamped on the back of it.
The 11/750 is divided up into a few different sections of backplane - starting from the right, there's the cards that comprise the CPU, including the UNIBUS and Massbus card(s). The bus that those are sitting on (the main CPU bus) is called CMI - Component Memory Interconnect, I believe. In the center, there's cards that are less "deep" which are memory boards - 1MB M8750's in my case. Finally on the left is the UNIBUS backplane. There's a small two-card "module" called a M9202 (which also has an LED for power status), with the cards connected by a 2ft piece of white UNIBUS ribbon cable that connects the small UNIBUS backplane back to the CPU backplane, and specifically the Primary UNIBUS interface card (L0004). Some information in this section is from The VAX 11/750 FAQ
First, the list and pictures of the primary CPU boards (from right to left in the backplane slots - the rightmost slot is slot "1".
One thing to watch out for is the power supply cables - there's some massive current available and one wrong move could weld you to it. That's why the VAX has a sign warning you to "remove watches and rings" when working in the machine. Anyways, the 2.5V / 85A power supply powers the gate array chips, and the 5V / 135A power supply powers all the logic in the machine.
The backplane in the machine has some jumpers on and connections on it that you'll need to change when adding/removing modules, or to change things like the console line baud rate. There's a diagram on the backplane cover, which I took a picture of for reference:
The control panel has the following functions:
Indicators
RESTART: "Simulates a power-off followed by a power-on." Basically just does a hard-reset of the machine
BOOT DEVICE: Chooses which ROM to use for bootstrapping, A is usually the TU58 on the console/control panel.
POWER ON ACTION: The 11/750 can contain a lead-acid battery that maintains power to the memory in the event of a power failure. VMS can "restart itself" from before the power failure if you have the switch in either of the two "RESTART" positions. The other two positions, BOOT and HALT, boot the system or leave the system at an SRM prompt when power is restored, or the RESET button is pressed.
Key switch: in effect when power distribution box switch is set to "REMOTE"
I don't yet have disk drives for the machine, but hope to get either some Massbus drives or (more likely) a UNIBUS SMD or some other type of drive controller. Right now, it's just got the "console" TU58 attached (which of course I don't have any tapes for), which doesn't do me a whole lot of good. TU58's provide 256KB on a compact tape cartridge. Yes, 256KB!! My first PC had that much RAM in it. Fortunately, though, there is a software TU58 emulator package called vtserver, which runs on a UNIX machine and emulates the TU58 software protocol over a serial port. So far, all I've gotten it to do is try to boot (which it can't) and halt at the SRM (dead-sergeant) prompt. I can enter commands, but can't do anything too useful until I get a TU58 image for it or something.
If you've got a spare UNIBUS disk controller, ethernet (DEUNA/DELUA) controller, Massbus disks, TU58 tapes or images of tapes for an 11/750, or any other VAX 11/750 information, drop me a line at "pat" at this domain (computer-refuge.org).
Last updated - Sat Feb 14 23:19:38 EST 2004
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