computer science

PDP-14

PDP-14 is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand PDP-14 rather than just read about it. In short: The PDP-14 was a specialized computer from Digital Equipment Corporation’s Industrial Products Group designed to replace industrial level relay controls for machinery and machine tools that performed repetitive tasks. It was specifically designed to function in the harsh electrical environment encountered in facilities where electric motors, solenoids and arc welders were present, a significant adversity for normal…

Key takeaways

PDP-14 belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect PDP-14 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of PDP-14 from memory before moving on to harder problems.

Reference excerpt

The PDP-14 was a specialized computer from Digital Equipment Corporation’s Industrial Products Group designed to replace industrial level relay controls for machinery and machine tools that performed repetitive tasks. It was specifically designed to function in the harsh electrical environment encountered in facilities where electric motors, solenoids and arc welders were present, a significant adversity for normal computer electronics. The PDP-14 was specifically designed to be the first level of factory automation, functioning as a programmable logic controller (PLC), through its ability to communicate with a standard DEC PDP-8 minicomputer. The first unit was delivered in June 1969 and used to control a gear grinding machine. Its design as a "programmable machine controller" was patented in 1973. The PDP-14 was designed to process Boolean equations, usually expressed as “ladder diagrams” and as such had a programmable read-only program (PROM) memory. Programs were developed using a PDP-8 then tested using a direct connection to the PDP-14. The PDP-14 was put into a check out mode where instructions were provided by the PDP-8. Following checkout, the PDP-8 provided the instructions to be put into the PROM. Later versions (for example, the PDP-14/30, whose instruction set was not binary compatible) are based on PDP-8 physical packaging technology. There also was a PDP-14/35 and a lower cost/reduced I/O capability PDP-14/L.

Hardware The 12-bit PDP-14 could hold a maximum of 4K words for instructions. The system's configuration included a control unit and a number of external boxes:

I-boxes (BX14) were for discrete inputs from the controlled system. Up to 256 input sources could be addressed. O-boxes (BY14) could control up to 255 actuators in the controlled system. A-boxes could be filled with timer modules for controlling time-driven events or retentive storage modules which were not cleared with power loss. A-boxes occupied the output address space along with the O-boxes. S-boxes were essentially the same as the O-boxes, but there was no real output device. This enabled storing intermediate results. S-boxes also used the shared output address space. Hence the combined usable output address space of the O-boxes, A-boxes and S-boxes was 255 or fewer.

Registers The PDP-14 has seven 12-bit registers:

IR PC1 & PC2 MB SPARE INPUT and OUTPUT.

Instructions Among the PDP-14 instructions were:

TRR – to move data between some (but not all) of the registers – TRansfer Register (contents). PC1 and SPARE have increment and decrement capabilities, permitting TRR to modify the value loaded into the register. JMS – JuMp to Subroutine – at the address specified in the following 12-bit word, saving the return address in PC2 JMR – JuMp to RETURN from a subroutine, jumps to location saved in PC2. In effect, JMR is a TRR in which PC2 is transferred to PC1. SKP – SKiP – is a TRR in which PC1 is incremented by 1. There were also TEST instructions (Test if something is ON or OFF) and SET instructions (SYN – Set "Y" oN, SYF – Set "Y" ofF).

Software The original PDP-14 required that programming be done by DEC. Subsequently, software development for the PDP-14 was done on another system, the PDP-8. A PDP-8 program named SIM-14 allowed for simulating the PDP-14.

Photos PDP-14 PDP-14's M740 Instruction decoder module PDP-14's M745 PDP-8 Interface

Worked examples

Example 1 — a first encounter with PDP-14

Start with the simplest possible case. Write down what PDP-14 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to PDP-14 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about PDP-14 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of PDP-14

In research: PDP-14 appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses PDP-14 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: PDP-14 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer-related introductions in 1973, DEC computers, Industrial automation, so understanding it makes those chapters shorter.
In everyday life: Look for PDP-14 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study PDP-14 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PDP-14 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain PDP-14 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PDP-14 in simple terms?

Why does PDP-14 matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study PDP-14?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on PDP-14.