computer science

TJ-2

TJ-2 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 TJ-2 rather than just read about it. In short: TJ-2 (Type Justifying Program) was published by Peter Samson in May 1963 and is thought to be the first page layout program. Although it lacks page numbering, page headers and footers, TJ-2 is the first word processor to provide a number of essential typographic alignment and automatic typesetting features: Columnation, indentation, margins, justification, and centering Word wrap, page breaks and automatic hyphenati…

Key takeaways

TJ-2 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 TJ-2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of TJ-2 from memory before moving on to harder problems.

Reference excerpt

TJ-2 (Type Justifying Program) was published by Peter Samson in May 1963 and is thought to be the first page layout program. Although it lacks page numbering, page headers and footers, TJ-2 is the first word processor to provide a number of essential typographic alignment and automatic typesetting features:

Columnation, indentation, margins, justification, and centering Word wrap, page breaks and automatic hyphenation Tab stop simulation Developed from two earlier Samson programs, Justify and TJ-1, TJ-2 was written for the PDP-1 that was donated to the Massachusetts Institute of Technology in 1961 by Digital Equipment Corporation. Taking English text as input, TJ-2 aligns left and right margins, justifying the output using white space and word hyphenation. Text is marked-up with single lowercase characters combined with the PDP-1's overline character, carriage returns, and internal concise codes. The computer's six toggle switches control the input and output devices, enable and disable hyphenation and stop the session. Words can be hyphenated with a light pen on the computer's CRT display and from the session's dictionary in memory. On-screen hyphenation has SAVE and FORGET commands and OOPS, the undo. Comments in the code were quoted thirty years later: "The ways of God are just and can be justified to man" and "Girls who wear pants should be sure that the end justifies the jeans." TJ-2 was succeeded by TYPSET and RUNOFF, a pair of complementary programs written in 1964 for the CTSS operating system. TYPSET and RUNOFF soon evolved into runoff for Multics, which was in turn ported to Unix in the 1970s as roff. A similar program for the ITS PDP-6 and later the PDP-10 was TJ6.

Illustrations

Worked examples

Example 1 — a first encounter with TJ-2

Start with the simplest possible case. Write down what TJ-2 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 TJ-2 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 TJ-2 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 TJ-2

In research: TJ-2 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 TJ-2 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: TJ-2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Desktop publishing software, History of software, Text editors, so understanding it makes those chapters shorter.
In everyday life: Look for TJ-2 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 TJ-2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what TJ-2 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 TJ-2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is TJ-2 in simple terms?

Why does TJ-2 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 TJ-2?

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 TJ-2.