computer science

TK85

TK85 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 TK85 rather than just read about it. In short: The TK85 was a ZX81 clone made by Microdigital Eletrônica, a computer company located in Brazil. It came with 16 or 48 KB RAM, and had a ZX Spectrum–style case, similar to a Timex Sinclair 1500.

Key takeaways

TK85 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 TK85 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of TK85 from memory before moving on to harder problems.

Reference excerpt

The TK85 was a ZX81 clone made by Microdigital Eletrônica, a computer company located in Brazil. It came with 16 or 48 KB RAM, and had a ZX Spectrum–style case, similar to a Timex Sinclair 1500. Unlike the ZX81, the TK85 used standard logic components rather than a gate array ("ULA"), and during manufacture several of them were scraped so that competitors couldn't easily copy the circuit. The circuit board had space for a AY-3-8912 sound generator chip (compatible with the ZonX-81 sound board), and although none came factory installed, it is possible to add the necessary circuits. The TK85 came with a copy of the 8K ZX81 floating point BASIC, and an additional 2K EPROM, mapped to addresses 8192–10240, containing machine code routines for use with tape files. These routines could save with HISAVE, load with HILOAD and verify with HIVERIFY in "Hi-Speed" (4200 bit/s); save and load, BASIC variables in 300 bit/s (standard ZX81 speed) using SAVE and DLOAD functions and 4200 bit/s (Hi-Speed) using DHSAVE and DHLOAD. These routines were all accessible using RAND USR commands. The save to variable function could be used to make copies of programs on tape. The expansion port on the back of the computer is compatible with the ZX81, although some peripherals may not work due to conflicts with the 2K of extra ROM. The rear of the computer featured a TV output (without video back porch), "EAR" and "MIC" sockets for connecting to an external tape recorder, a joystick port using a DIN socket (that simulated the 5,6,7,8 and 0 keys), a ZX81 compatible expansion port, space for a sound output socket, and a socket for the 9V external power supply. Since the joystick used the cursor keys, and due to the circuitry for the keyboard, it wasn't possible to detect diagonal directions correctly.

References

External links Microdigital TK85

Illustrations

Worked examples

Example 1 — a first encounter with TK85

Start with the simplest possible case. Write down what TK85 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 TK85 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 TK85 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 TK85

In research: TK85 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 TK85 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: TK85 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer-related introductions in 1983, Computer hardware stubs, Goods manufactured in Brazil, so understanding it makes those chapters shorter.
In everyday life: Look for TK85 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 TK85 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what TK85 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 TK85 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is TK85 in simple terms?

The TK85 was a ZX81 clone made by Microdigital Eletrônica, a computer company located in Brazil. It came with 16 or 48 KB RAM, and had a ZX Spectrum–style case, similar to a Timex Sinclair 1500.

Why does TK85 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 TK85?

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 TK85.