I was originally thinking along the lines of pdp-8 or pdp-11... I guess I'm not familiar with VAX yet...
Hmm... PDP-8 or PDP-11... that narrows it down to about 100 models.
I'll re-sequence your questions a little, and restrict myself to the PDP-11's. (Someone else will advise about others)
- What all does one of these machines need to work?
Models were available in many countries, and had differing power capabilities. It would be important to know where you live to answer this.
Also, models ranged from
Desktop to
Floor Stand to
Rack Mount to
Refrigerator size [Sub-Zero if you please] and consumed hundreds to ten-thousands of watts. [more if multiple large disk and tape drives were in use]
Power needs ranged from simple
110VAC 1PH to
220VAC 3PH, depending on which. Most systems were 50 or 60 hz operable. Amperage from
20A to
600A, again - depending on overall system size and to some degree, age.
Older disk drives are becoming more and more of a problem to get supplies and parts for. Moreover, removable cartridge drives required routine preventative maintenance - air filters, brushes, bearings and spindles etc... all of which are now unavailable and are critical to fault free operation. Fail to perform PMs and your drives will quickly become inoperable, and your media permanently physically damaged.
RL media for example, although rugged, can be damaged to the point where it's original format has been overwritten, and this cannot be subsequently re-formatted.
RM or
RP drives and media are
more rare and even more maintenance dependent.
Smaller machines had only "comfortable" atmospheric and Air Conditioning needs, where larger systems required
CTCH of a more rigorous nature.
One attribute often not considered is
system weight. Hardly any older systems weigh less than
hundreds of pounds - if not
thousands. Newer, more common "Floor Stand" types with self contained media probably weigh in mostly in the sub
100 LB range, but almost always over ~
50 LBS.
- What should I expect to pay for a working set up?
The sky is pretty much the limit these days. It seems if you've the patience, you can still piece a system together for
hundreds to thousands. Complete systems of the larger (and older) physical variety come along less and less frequently nowadays and I would expect to be able to land them for
Thousands to Ten-Thousands depending on the rarity, condition and completeness of the system.
- What model would be best to look for, for a noob?
Here's the real issue - PDP-11's are like Real Estate...
they ain't makin any more, so you'll be better off buying sooner than later. If you have the resources, jumping in at the deep end of the pond now will save you much more money than if you wait till you're experienced - down the road.
On the other hand, it's easy to make costly mistakes, both in purchasing and use. We cry a lot when noob mistakes destroy equipment - which is very easy to do - and anyone can "get taken advantage of", in a sale.
Operating Systems:
You haven't mentioned a purpose to your interest, or any specific software you'd like to be able to run. A museum for example, would be safe going for a large system with lots of variety of memory and media and be fairly secure in the knowledge that they could run any DEC Operating System of appropriate vintage with suitable hardware and options.
On the other hand, if for example your interest was primarily in early
Bell Labs UNIX OS's, the required minimum hardware set would be considerably less difficult to collect.
If the OS is not on your radar as yet, a good general purpose "Single User" system for a novice would be
RT-11. It's compatible with the broadest range of hardware configurations and is readily available over the internet. It also supports a pretty good smattering of devices and languages so will be "usable".
UNIX support of hardware varies quite a bit with the vintage, as one would expect. However, once running - expectations are more easily met because of it's longevity and current use in todays world [as long as your comfortable with a text user interface]
RSX seems to be of little interest to the hobbyist, and I do not recommend it unless you want to delve into the attributes of early, Multi-User, preemptive, realtime OSs. However if your interest does lie here, RSX is a most sophisticated OS and exceeds complexity of many more modern counterparts. [IMHO]
There are other OSs too,
RSTS,
CAPS-11, and more. Also a pre-OS type software can be fascinating to study too.
A quick guide to PDP-11 Models:
- In the beginning, DEC created UNIBUS, and it was good.
- DEC added more bits to the UNIBUS, and it prospered. (up to 18 bits)
- Then DEC created Memory Management and Mapped Systems were born. The king of these being the PDP-11/70 - a PDP-11 CPU with Supervisory Execution modes that accessed 32-bit memory via CACHE and contained separate I/O buses. 1 UNIBUS and up to 4 MASSBUSes. PDP-11/74 s could contain up to 4 such CPUs.
- In general, PDP-11's are distinguished by the BUS type - UNIBUS and QBUS (first called LSI-11 bus)
- Early CPUs were implemented in discreet LS logic. Most of these had console "Switch Registers". Later, CPUs were implemented using custom LSI and VLSI and then an early form of VLSI HCMOS. Their front panels dropped the Lamp / Switch Register in favor of requiring and inclusion of a Serial Console Terminal.
Eventually a
CPU type numbering system evolved where
even numbered models were
UNIBUS and
odd numbered ones were
QBUS. Unfortunately, early systems violate this thinking, for example - an 11/02 was a QBUS machine constructed with LSI [Large Scale Integrated Circuits] where an 11/05 was UNIBUS consisting of discreet IC logic. Likewise the 11/45 was UNIBUS.
Also, a timeline of Systems will be confusing. The model numbers denoted families, based on capability - not necessarily sequence. An 11/70 was first available much earlier than it's numeric value might imply. An 11/03 came much later.
Lastly, the Family notion is to be taken more literally on PDP-11's than perhaps on any other computer. Software which ran on earlier machines, almost always ran
unaltered on later models with more instructions and capabilities. This was known as "Upward Compatibility", and was a novel architectural asset not often found in other systems of the time. Device controllers for UNIBUS were often so compatible with their QBUS counterpart, that no customization of software drivers was required to run in either environment. Truly, a "Family" approach in many dimensions.
Ok, that's enough writing. If I haven't scared you off - supply us some feedback to get a useful line of discussion going.
