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DEC: The best of systems, the worst of systems

Digital Equipment Corp's hits and misses

By Geoffrey G. Rochat, 11 Feb 2011

Opinion Which were the greatest DEC computers and why? Which were the worst - and why?

Everyone has their own definition of greatest and worst, and exemplars of each, but I'm looking at the machines that had the most or the least influence. Since DEC under Olsen got a lot of things right, it's quicker and easier starting from the bottom.

The misses

The PDP-4, a follow up to the original PDP-1: The PDP-4 was 5/8ths the performance of the PDP-1 for half the price, and that just didn't cut it.

The Rainbow:  A complete misreading of what a PC should be.

The PDP-11/60: Intended to be a reliable, maintainable mid-range PDP-11, it couldn't be maintained and was unreliable. The Rhode Island Computer Museum has in its collection nearly every flavor of PDP-11 ever made, with the notable exception of the PDP-11/60. They've never been able to find one.

The PDP-8/S, a serial implementation of the PDP-8: It was intended to be a minimal implementation of what was a minimal computer architecture. It was clever, and in a notably small package (for its day), but it was too slow to get out of its own way. It was rapidly obsoleted by IC (integrated circuit) technology.

I must also admit to not being a fan of the VAX architecture, which, to some people, is sacrilege. I like computer architectures that are simple, clean and elegant, none of which characteristics the VAX has.

I always got the impression that Gordon Bell's people never understood that, just because you can add a feature, it doesn't mean you should. Of course the VAX was wildly successful, with an army of devotees unto this day, so one can't exactly say it was among DEC's worst efforts. But it was not their best.

Don't get me started on the Alpha

The hits

Now from the top:

The PDP-1: While clearly a "first effort" design full of things we now know could have been done better, the PDP-1 is technologically important in that it brought the idea of small, cheap, interactive computers to the world. Had there not been a PDP-1, we'd still be communicating by post with letters written on typewriters.

That you can type something into a computer and edit it in real time, display it on a screen, then send it elsewhere, is all the legacy of the PDP-1.

The PDP-7: in spite of itself. The PDP-7 was the successor to the PDP-4, and was something of a mess mechanically and thermally. (I spent four years working with a surplus PDP-7 that was held together with tape and bailing wire, so I have a particular fondness for the type.)

Unix was first implemented on a cast-off PDP-7, earning the machine a place in computer history it probably would not otherwise have deserved. PDP-7s tended to be more productive after their nominal working lives ended, when people got the chance to play with them without "adult supervision" than during them.

The PDP-10 series:  For a long time everybody's first computer - via timesharing. The architecture was elegant, the tools were superb, the operating system has never been bettered, anywhere, and the things were rock solid. The PDP-10 was the pinnacle of everything that DEC got right. And then DEC murdered it in favor of the VAX.

The PDP-8/e: For the first time, all the pieces that made up a minicomputer system came together:

A workable architecture.
A powerful resident operating system (OS/8), supported by tools and compilers galore.
A rational bus (Omnibus) that allowed easy system expansion and the ability to roll-your-own custom devices.
The right packaging.  
Documentation that told you *everything* and...
A rabid user group (Decus) that provided tons of free code, sort of an early open-source movement long before anybody coined the term.

The PDP-8/e was enormously successful in its day.

The PDP-11/34: In some ways the 16-bit successor to the PDP-8/e, the /34 was the right-sized machine, for the right price, for an awful lot of applications. As semiconductor technology progressed the PDP-11/34 was supplanted by the PDP-11/23; the same ideas, but for a lower price.

OK, that's my list. Ask any N retro-computing enthusiasts and you are likely to get at least N lists, all mutually incompatible. And the "discussions" that ensue when listers compare lists is most amusing - particularly when experienced from a safe distance. (Be prepared for an extended performance. Earplugs are recommended. So is a fire extinguisher.)

Before closing, let me posit a thought. My list of DEC machines is certain to be controversial, as would be anybody's list, but that's nothing. If you want to start a real column-inches-filling flame war, once the battle among DECies calms down, pose this question:

Which was better, the PDP-11 or the [Data General] Nova?

But first, make sure you're within dashing distance of your fallout shelter. ®


I'm one of those old-timers who worked on with the PDP-1 (although well after its heyday), as well as the PDP-5, PDP-6 (a 36-bit mainframe), PDP-7, PDP-8 series, PDP-9, PDP-10 series (the successors to the PDP-6), PDP-11 and PDP-12 (a combination PDP-8 and a specialized DEC computer called the LINC). I never got to work on a PDP-15, but one can't have everything.

I was the Vice President of the Rhode Island Computer Museum, and am a member of the Retro-Computing Society of Rhode Island, both of which have large collections of minicomputers. I myself have several flavours of PDP-8s, in various stages of disrepair, as well as PDP-11s, an HP-1000, and several other vintage machines.

"The" Computer History Museum on the Left Coast (as though there's only one...) gets all the retro-computing limelight, even though a lot of its collection was once in the defunct Boston Computer Museum, and the retro-computerists in New England are left shivering in the cold and dark.

Both the Rhode Island Computer Museum and the Retro-Computing Society of Rhode Island are strictly volunteer organizations that are doing what they can to preserve our technological history, and mentioning them might get them a little well-deserved publicity.

I don't know what it is about Rhode Island, but there are a lot of folks there who collect old kit. In addition to the RICM and the RCS/RI, there's also the Warbirds Museum at Quonset Point, full of old aircraft, and the New England Museum of Wireless and Steam, with two huge collections, one of pre-WWII radios (including the entire Massey Point Judith spark station, with building), the other of running stationary steam engines. Maybe it's the water or something...

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