Computer Science

Common mistakes in systems and networks

4 mistakes learners make with systems and networks, each one named and explained.

All common mistakes

Each component and each layer has one job, and the jobs are not interchangeable.

A computing term given the wrong meaning

What it looks like

Compiler is defined as interpreter, or a database term is matched to the wrong clause.

Why it happens

The vocabulary is large, precise and learned as definitions, so close terms trade places.

A worked example

Question. What does a compiler do?

A common answer. Runs the code line by line as it goes

The answer. Translates the whole program into machine code before it runs

Why. A compiler translates everything first and produces an executable. An interpreter translates and runs line by line.

Put the two side by side

An interpreter works line by line, at run time.
A compiler translates the whole program first.

Learn each term with what it does and when it does it.

A network component or protocol given the wrong job

What it looks like

A router is described as doing a switch's job, or a protocol matched to the wrong task.

Why it happens

The components sit in the same diagram and the acronyms are learned as a list.

A worked example

Question. What does a router do?

A common answer. Connects devices within one local network

The answer. Connects different networks and forwards traffic between them

Why. A switch connects devices inside a network; a router joins networks and decides where traffic goes next.

Put the two side by side

A switch works inside one network.
A router works between networks.

Say what each device connects, and the roles separate.

One logic gate taken for another

What it looks like

AND is used where OR belongs, so the output is right for only one input pattern.

Why it happens

Both gates take two inputs and give one output, and the words and and or are used loosely in speech.

A worked example

Question. An AND gate outputs 1 when:

A common answer. either input is 1

The answer. both inputs are 1

Why. AND needs every input true. OR needs at least one. The truth table settles it in one line.

Put the two side by side

OR outputs 1 if any input is 1.
AND outputs 1 only if all inputs are 1.

Write the truth table rather than reasoning from the word.

The roles of memory types swapped

What it looks like

RAM is described as permanent, or ROM as the working memory a program runs in.

Why it happens

They are named as a pair and both hold data, so which one survives a power cut gets reversed.

A worked example

Question. Which memory loses its contents when the power is off?

A common answer. ROM

The answer. RAM

Why. RAM is volatile working memory. ROM keeps its contents without power and holds the start-up instructions.

Put the two side by side

ROM is permanent and read mostly.
RAM is temporary and read and written constantly.

Tie each to what happens when the power goes off.

WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.

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