Digital Equipment Corporation PDP-11 Recognition


The DEC (Digital Equipment Corportation) PDP-11 is now a favourite with vintage computer enthusiasts, for several reasons: Some are still showing up at scrappers, and this page is an attempt to make it easy for the operators of such places to recognize PDP-11's - almost all of which are worth more, as vintage computers, than as scrap. (You can click on essentially all the images below to see a larger version.)

Note: DO NOT just keep the boards, and discard the box, bulkhead panels, cables, etc. Everyone does that, as a result of which we are now over-supplied with boards - but the cables, boxes etc are now rare (un-obtainium in some cases, such as UNIBUS and RL0x cables). These are all now worth a lot more than the cards are!

The tables below include a rough idea of the value, based in most cases on recent sales history. Ones which are pure guesses are marked with a '?'. However, don't put too much stock in these numbers: a number of factors will cause them to vary considerably from the numbers given here:

The first can have a large effect; inclusion of a large tape drive and some large disk drive (each fairly valuable in their own right) can have a big upward impact on the value. To illustrate these factors at work, I have seen a PDP-11/70 with magtape and MK11 memory system in two 6' DEC racks go for over US$10K on eBay when a number of high-end collectors went for it; and as an example of the importance of the last factor, I heard of one collector from the UK who was arranging to fly to the US to arrange shipping back to the on a PDP-11/40 in a 6' DEC rack - only to be outbid by another collector at $10K!


The reason this section is first is that some models are to be met in both rack and table-top forms - so in the pictures of the various models in the next sections, realize that they may also appear in a rack, not just as the smaller unit shown. For most, the mounting boxes were originally mounted in racks, in slides (see below).

PDP-11's come in a variety of different mounting racks (all usually the standard 19 inches wide, although some have a side-bay which increases the width). Some of the racks (e.g. the H960's, below) are from DEC, and are the racks many PDP-11's came in originally, and are thus now rare and desirable, and thus valuable in their own right.

There are a whole line of accessories for the H960 series, many of which are also now rare, and thus valuable. The top picture shows a rack with one of them - the pink and purple plastic 'advertising panel' at the top (panels with other colour scheme are also to be met with, and are also desirable). Pictures of some other items are shown below.

In addition to the items shown, there are also rear full-height swing-out frames (just a plain rectangle, made of square cross-section tubing) for the H960, which are now quite rare.

Also, rack-mounted units (not just CPUs, but also disk drives, etc) were usually rack-mounted on slides; these come in an 'outer' (mechanically attached to the rack), and an 'inner' (mechanically attached to the unit). When many systems were taken apart, people just slid the units out, and usually didn't bother dismounting the outers and putting them back with the inners, so the outers as also now hard to find, and thus of value.

Image Model Size Value Comments
H960 72" H x 22" W x 30" D $200-500 The original PDP-11 cabinet, now the most sought-after. If it has any of the original accessories (sides, back door, extension feet on the front, the logo panel at the top, and blank panels on the front), each of those will add to the value. (Technically, the bare frame is an H950; 'H960' refers to the complete unit, including the accessories.)
H960 side panel 72" H x 30" W x 1/2" D $50-$150? Side panels are somewhat rare because when a number of racks are joined together, all the intermediate racks don't have side panels. The image shows the inside face; the outside is totally flat.
H960 rear door 72" H x 20" W x 1/2" D $50-$150? Rear doors are also rare, although the reason is not obvious; perhaps they just got in the way? This image too shows the inside face; the outside is also totally flat.
H960 filler strip 72" H x 1" W x 2x" D $50-$150? Filler strips are used in pairs between each pair of racks; they are cruciform in cross-section (see right-hand image). Very rare.
H960 stabilizer feet 2" H x 2" W x 8" D (each side) $50-$150? (each) These are not just decorative; when units in the rack are slid out, it will topple forward without them. As castings, they will be hard to reproduce. There is also a kick-plate running between the two.
Full blank front panel 10-1/2" H x 19" W x 1" D $20-50 The front of the rack has blank panels to fill empty spaces where equipment is not mounted. These are also much in demand.
Half blank front panel 5-1/4" H x 19" W x 1" D $20-50 Even though they are half the size of the full panels, they are worth the same since they are currently rarer.
Logo panel 4" H x 20" W x 2" D $40-50 (blank)
$80-150 (lettered)
These go at the top of the rack; in addition to the one with lettering (shown), there are also blank ones, with just the two color blocks. In addition the PDP-11 ones, shown here, there are ones for other DEC computers, in different colors.


All the early -11's were based around a bus called the UNIBUS; these machines are grouped together because they are (mostly) the largest, oldest, and most valuable of the PDP-11's.

Almost all the UNIBUS PDP-11's all had distinctive front consoles which were an integral part of the CPU (and thus could not be changed), enabling them to be identified at a glance purely externally. The only exceptions are the 11/84 and 11/94; an /84 could be upgraded to a /94 by swapping the CPU card.

It is not uncommon to find PDP-11's with custom printing on the front panel, produced by both DEC and OEMs. The thing to look at is the configuration of the switches (and knobs, if any): this never varies, from model to model (although on occasion one finds custom switch colours too).

Image Model Year of Introduction Value Comments
11/20 - 11/15 1970 $2-3K The original PDP-11, now one of the most sought-after. The 11/20 and 11/15 are very slightly different, but are basically the same machine.
11/05 - 11/10 1971 $1-2K The 11/05 and 11/10 are the same machine; the latter is a re-badged version for the OEM market, instead of end-users, differening only in the number painted on the front panel.
They are to be found in both 10-1/2" high (as here) and 5-1/4" high boxes.
11/45 - 11/50 - 11/55 1971 $4K These are all basically the same machine, differing only in the kind, and amount, of memory they were supplied with (and the number painted on the inlay of the front console). The CPU is identical in all three.
11/35 - 11/40 1973 $4K-$5K+ The 11/35 and 11/40 again are the exact same CPU, differing only in the number on the front panel, and usually the box they are in (10-1/2" for the /35, and 21" for the /40 (although that's not a hard-and-fast rule, exceptions have been seen). The former is a re-badged version for the OEM market, instead of end-users.
11/70 1975 up to $10K+ The largest PDP-11, and the last with a full switch panel. DEC produced them with both the blue colouration (shown here) and the red/purple colour scheme of the other PDP-11's (above).
(Later 11/70s often had a remote diagnostic console, which omits the lights and switches, and are thus worth considerably less.)
11/04 1975 $1K Both the 11/04 and 11/34 (following) may come with either the programmer's console (shown below on the 11/34) or the 'normal' console (shown here); the two are otherwise externally visually identical. These too are to be found in both 10-1/2" high and 5-1/4" high boxes.
11/34 1976 $1K Either the 11/04 or the 11/34 can appear with this console; the programmer's console is much more desirable than the normal console, and will add several hundred US$ to the value. The consoles only differ in the number printed on them.
Probably the most common PDP-11; again, to be found in both 10-1/2" high and 5-1/4" high boxes, although usually the former.
11/60 1977 $6K? An extremely rare (and desirable) -11; the rarest of the UNIBUS PDP-11s.

(The image is of the front console only, not the entire machine; nonetheless, all PDP-11/60's will contain this panel, making them easy to identify.)

11/44 1980 $1-2K The last of the 'pure UNIBUS' PDP-11's.
11/24 1981 $700-1K A UNIBUS version of the -11/23. Found in both 5-1/4" and 10-1/2" boxes.
11/84 1985 $1K This has a QBUS PDP-11 KDJ11-B CPU board (see below) hiding inside it.
Image coming 11/94 1990 $4K Also had a QBUS PDP-11 (a KDJ11-E) hiding inside it. This is the last PDP-11.


DEC later introduced a cost-reduced bus called the QBUS; a number of later PDP-11's were built for it.

Unlike the UNIBUS CPUs, the QBUS CPUs did not have an integral front console, so there's no external clue to tell you what kind of QBUS PDP-11 one has. To make things worse, all QBUS PDP-11 CPU's are a single card, and they are (basically) plug-compatible. So sometimes a box initially shipped as one kind of QBUS PDP-11 (e.g. an -11/23) was later upgraded to something else by swapping out the CPU card.

So the only definitive way to know which kind of QBUS machine one has is to examine the CPU card. However, it's not really necessary to do that - all the QBUS machines are worth roughly the same, so if one can tell that one has a QBUS PDP-11, one knows roughly how much it is worth. The one exception is the -11/93, which is very rare, and worth a lot more than any of the others.

An additional complication, for the QBUS PDP-11's, is that companies other than DEC made the boxes for them. The most common is Sigma Systems, but there are several others, including Plessey.

So the tables below show first the PDP-11 CPU cards (prices given are for the CPU card alone), and then the various DEC QBUS boxes. (Other manufacturers made memory, I/O cards, etc, but basically only DEC made CPUs - until after they sold the PDP-11 line off to a company called Mentec.)

Image Model Date of Introduction Value Comments
LSI-11 1975 $100 The original QBUS PDP-11; limited memory, and cannot run most time-sharing PDP-11 operating systems; valuable only for its historic nature. Several models exist, with and without on-board memory, etc.
LSI-11/2 1975 $100 The same CPU chips as the board above, but in a dual-width card without anything else on it.
11/23 (KDF11-A) 1979 $75 Probably the most common QBUS PDP-11. The basic version has one large plug-in chip, more advanced models have a second (as here), and possibly a third, each with a slight ($25) increment in value.
11/23-PLUS (KDF11-B) 1979 $150 The same CPU chips as the one above, but packaged with several serial lines, ROM, etc.
KEF11-B Commercial Instruction Set option chip 1979 $200 A very rare option chip for the two boards above, but usually only seen on the second type; of considerable value by itself.
11/73 (KDJ11-A) 1983 $100 The power of a PDP-11/70 in a much smaller, and cheaper, box.
11/83 (KDJ11-B) 1985 $250 The CPU from the QBUS-only equivalent to the 11/84. Note the large chip in the upper right; this is the the FPJ11 floating point accelerator. This is again very rare, and of considerable value on its own; occasionally seen on the board above, too.
11/93 (KDJ11-E) 1990 $2-3K The CPU from the QBUS-only equivalent to the 11/94.

As mentioned above, these are some of the boxes in which QBUS PDP-11's
are to be found:

Image Model Date of Introduction Value Comments
Image coming BA11-M 19xx $200 The original QBUS mounting box.
BA11-N and BA11-S 19xx $100 These two mounting boxes are almost identical (modulo various appliques on the front panel), and differ only in the power supply and backplane inside. The -N has an H786 Power Supply; the -S has the slightly more powerful H7861. The backplane in the -N is the H9273; that in the H9276.
Image coming BA23 19xx    
Image coming BA123 19xx    
Image coming BA213 19xx    

PDP-11 boards

All PDP-11 boards are, in physical form, variants of the 'single-width' card below:

They come in dual- and quad-width form (seen above, with the various QBUS processors), and also hex-width. The key thing to note is the configuration of the gold-plated contact fingers on the edge; anything with this physical form is almost certainly a DEC card. (They also used them in machines other than the PDP-11, such as the PDP-8, PDP-10 and PDP-15.) In the dual and larger cards, note also the size and shape (with the keying cutout) of the gap between the contact groups; these are also a 'fingerprint' for DEC cards.

The value will vary tremendously, depending on their desirability (demand) and rareness (supply). To find out the value, one need to know the board's module ID, which is usually printed on the metal or plastic insertion handles. (DEC produced thousands of board types, and so knowing the module ID is crucial to knowing the value.) This ID will have the form YXXX or YXXXX, where 'Y' is a letter (most often 'M' or 'G', but others are to be found too), and 'X' is a digit. Other numbers can often be found in the etch, but these are usually DEC internal part numbers for the bare board, and are usually useless for looking them up. Find the module ID (XYYYY).

These number are given on the plastic insertion handles, as shown:

and similarly on one of the tabs of the metal insertion handles (exactly which one varies from board to board):

The older boards will usually say "FLIP CHIP" on them somewhere; this was a DEC trademark, and thus will appear only on real DEC gear. Later boards tended to drop this, but they often contain the 'Digital' logo:

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Last updated: 29/May/2021