MicroVAX 3100-30
miod > machineroom > manufacturers > Digital > MicroVAX 3100-30

The MicroVAX 3100 family

The MicroVAX 3100 family, when introduced, was a low cost VAX range marketed as ``office server systems''.
There were two distinct MicroVAX 3100 families: the first one was intended to replace the MicroVAX II, and was built upon CVAX processors running at 11.1MHz (models 10 and 20) or 13.3MHz (models 10e and 20e). A few years later, a new set of MicroVAX 3100 were introduced, consisting of four different models: two entry-level models (30 and 40) based upon the same motherboard (using SOC processors) but different enclosures, similarly to models 10 and 20, and two higher-level models (80 and 90) running faster processors (Mariah for the 80, NVAX for the 90) in the model 40 enclosure. Model 40 could be upgraded to a model 80 simply by replacing the motherboard, and model 80 could be upgraded to model 90 similarly.

Here is a short summary of the different models, borrowed from Digital's MicroVAX 3100 Systems Comparison Chart:
Model Enclosure CPU type and speed L1 cache size L2 cache size Maximum memory capacity
10BA42-ACVAX, 11.1MHz1KBnone32MB
10eBA42-ACVAX, 13.3MHz1KBnone32MB
20BA42-BCVAX, 11.1MHz1KBnone32MB
20eBA42-BCVAX, 13.3MHz1KBnone32MB
30BA42-ASOC, 25MHz6KBnone32MB
40BA42-BSOC, 25MHz6KBnone32MB
80BA42-BMariah, 50MHz2KB256KB72MB
90BA42-BNVAX, 72MHz10KB128KB128MB

I am ashamed to admit that I have no recollection of how I got this machine. It is very unlikely that I ever paid for it, so it must have been either something found on my doorstep (i.e. a donation), or an extra collected while buying something else (``Hey, while you're there, would you mind picking that VAX?'').
What I remember very well, on the other hand, is that this machine used to be the webserver for gentiane.org for years, you may notice it near the bottom of the so-called ``tower of babel'' in the 2003 machineroom pictures. And I am considering making it the local webserver again.


(Click on the pictures to get larger resolution images)
The BA42-A enclosure is a pizzabox-like slim case, yet heavy as the whole case is made of steel. It has room for three internal devices, and one of them can be a removable device (either a floppy, tape, or CD-ROM drive), using a different front bezel.
(An example of the larger BA42-B enclosure can be found in the VAX 4000/106 page.)
Opening the case is straightforward: remove the two captive screws at the back of the chassis, and the whole cover slides towards the front of the case.
As usual with that kind of enclosure, the power supply is on the side, with the motherboard being partly covered by the drive tray. This machine currently has a 1GB SCSI disk drive. It used to have its two original drives, noisy Digital-branded RZ23 and RZ24 (100MB and 200MB respectively)...
Here is a better look at the drive tray with the drive removed. There is room for two 3"1/2 devices, in horizontal position, in the left half, and one 3"1/2 or 5"1/4 device, in vertical position, in the right half. The drive in the previous picture is not in its canonical place, but I think this allows for better airflow inside the enclosure.
This is what the motherboard looks like, with the drive tray removed. Nothing fancy to mention: the processor is the large chip on the lower right quarter, most of the I/O devices are close to the rear connectors.
Here is a better view of the motherboard, with all the connectors removed. Near the top of the board (which would be the rear of the case), the blue connector is the external SCSI connector.
The two black connectors to its right are connectors for the serial port expansion boards; these boards plug themselves into the high-density connectors near the processor (as two columns: each board using one of the two connectors below the processor, and one of the two connectors below the memory slots), and have their external ports (mounted at the rear of the chassis) connected to one of these black connectors.
Above the leftmost black connector, the square chip is the AMD ``LANCE'' Ethernet interface; its companion (``media interface'', before the MII days) chip being the brown chip immediately above the blue connector.
Immediately below these blue and black connectors are the six memory slots; memory is added in pairs of 4MB SIMMs. Since there are 8MB onboard (in the middle of the motherboard), the system can accomodate from 8MB (with no SIMMs) to 32MB (with six 4MB SIMMs) of memory.
Under the memory slots, the black connector on the left is the internal SCSI cable connector, to which the drive tray attaches.
Then, further down, the middle of the board is filled with the on-board memory. On the left side, under the memory, the two large horizontal chips are the motherboard's EEPROM. Immediately next to them, on the right side, is the SCSI controller, a good old NCR53C94.
To complete this tour, let's have a peek at the rear of the machine. Nothing special to see...
The top row sports the two optional serial option board external connectors, and the external SCSI connector.
The bottom row sports, from left to right: