Bringing Back the PDP8

Anne Thwacks writes " Andrew Grillet has decided that the Digial PDP8 - the first ever minicomputer, will rise from the dead. He is calling it the PDQ8. Sure others have done software emulations, and even hardware clones, but he is not just building a hardware clone, but trying to revive the whole idea of 12 bit computers!"

Comments

12 bits

[vasqzr]

I found that, where you are not primarily handling ASCII, 12 bits was a very good size.


Maybe someone would enlighten the rest of us on why a certain bit size is better than another, and why we currently use 8/16/32/64, instead of 12/24/48/96 ?

Re:12 bits

[FauxPasIII]

>> Maybe someone would enlighten the rest of us on why a certain bit size is better than another,
>> and why we currently use 8/16/32/64, instead of 12/24/48/96 ?

Because powers of 2 are easier to work with in binary.

This is great news :)

[solostring]

I fondly remember the PDP8. My father had one installed in the garage when I was a kid, and had my first experience of programming on it when I was 8 or so.

On the subject of PDP8's, I was surprised to hear that they were used in communications in Hong Kong up until at least 1999 for a number of financial institutions. I worked with an old computer technician who earned a fortune maintaining these beasts. I wonder if they are still being used in HK after the Chinese reclaimation?.....

Why?

[BWJones]

but he is not just building a hardware clone, but trying to revive the whole idea of 12 bit computers!"

So, after reading the article, I am still trying to figure out....Why revive the idea of 12 bit computers? Other than nostalgia (which is why people still drive Studebakers, old Ferraris and old Porsche's I suppose), what is the point?

Text based games

[Technician]

I remember playing the father of the Zork series of games on a PDP 11/35 which was the newer 16 bit machine. The game was called Adventure. We got the game on a 5 Meg 14 inch hard drive (RK05) and wasted a bunch of paper making moves on a keyboard/printer terminal. The scrollback feature of the hardcopy was great for finding your way out of a maze again. Adventure has since been ported to CPM and DOS. The game is still a great game and will challenge the thought process. Take a pencil and paper to keep from getting lost. There is no map. Do a google search to find this true classic game. You should be able to run it in a DOS window on Windows 95 before DOS and Windows 95 expire at the end of this year. I'm still trying to figure out who the shadowy figure is who tries to get my attention.

Didn't these things have selectable word sizes?

[GreyPoopon]

I remember seeing one of these puppies when I was in high school. It was no longer in service, but still had most of its internal components. In fact, I still have one of the "flip chips" that I took from inside it. Anyway, I believe I recall a dial on the front of the main panel that allowed you to choose the word size. I can't remember whether 12 bits was the minimum or the maximum, though. Can anybody verify that this existed, or am I just remembering some strange dream?

PIC is a bit more practical

[Bruce Perens]

If you want to program old microcomputer architectures, learn the PIC microcontroller, which is based on some Control Data Co. Peripheral and Input Controller (I may have the "I" wrong in that acronym). It's available in 12, 14, and 16-bit flavors. It doesn't have much of a stack. And it has the virtue that, as a $1 microprocessor, it's still practical for many projects, while a PDP-8 is really an intellectual exercise at this point.

Bruce

I loved the PDP-8 but I'm not convinced...

[dpbsmith]

Until I actually started programming a PDP-8 (in assembly language, of course), I would never have believed that you could program comfortably in such a seemingly restricted instruction set. And, conversely, when I moved to a PDP-11, I thought I was going to revel in the freedom and power of all those instructions, all those registers, those addressing modes, those index registers... and the ability to access 65536 bytes directly.

If C is "high-level assembly language," then the PDP-11 is "a computer that directly implements C."

To my surprise, though, I didn't really find that a lot was gained. Programming a PDP-11 didn't really FEEL much easier or more powerful than programming a PDP-8. And it was amazing how much every program expanded in size. It's been said that the PDP-8 instruction set was the most core-efficient ever devised, and I'd believe that.

On the other hand, when I tried programming a 6502, which on the face of it doesn't SEEM that much more restricted than a PDP-8, I just about went bananas.

Having said all that, I'm still not sure I see the point. The sweet design for a computer has to depend on the economics of the hardware around it. Who cares? Even IF the "core-efficiency" thing were true, and even IF you could use standard RAM with a 12-bit processor and not waste any bits, and even IF it turned out that the PDP-8 design were, say, 30% faster and used 30% less RAM for a given program than x86... how could it matter?

If the Alpha, which really WAS a superior design, wasn't superior enough to overcome Intel marketing, customer inertia, and only the normal amount of mismanagement, how can a PDP-8 be anything more than a curiosity?

PDP-8 microprocessors

[panurge]

This is so long ago I can't even remember the manufacturer, but there were at least 2 CMOS implementations of a PDP-8 processor. Has anybody observed that the instructions were based around core memory, so the accumulator was cleared when it did a store? If you could get the core again, a home computer with a PDP-8 processor and core memory would really benefit from a modbox with windows and lights.

For some industrial control jobs, something like a PDP-8 or PDP-11 is in many ways ideal because you can see everything that goes on. It is actually possible for one person to understand the hardware, the microcode, and every single bit of the software. For me, that is the great pleasure of small embedded designs. I really think it would be good to have a teaching tool for CS that actually meant that the student could do a project and have a complete overview of the entire thing in this way. I'm far from knocking progress, but there are comments on this thread that are a bit about the kind of alienation we have now between hardware and software - most people have no real idea at all what the hardware does, and use terms like "cache" without even stopping to think about what is going on. So yes, let's have someone build an understandable modern PDP-8. It's less weird than the RCA1802 and easier to get your head around than the 8080.