Lesson 1 of 5
Why computers store everything as 0s and 1s
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Big ideas · 1 of 10
Big ideas
Do this: Read each idea. Then say why a computer uses only 0 and 1.
A computer is built from huge numbers of tiny electronic switches, each with two states: on or off.
We write on as 1 and off as 0. The 0s and 1s are how we write down what the switches are doing.
One 0 or 1 is called a BitOne 0 or 1. The SMALLEST piece of computer data.Exactly: A binary digit: a single 0 or 1. It records the state of one switch, off or on.Mix-up alert: A bit is not a byte. It takes 8 bits to make 1 byte.See this in Key words, the smallest piece of data a computer stores.
Eight bits grouped together make a ByteA group of 8 bits.Exactly: Eight bits handled together. One byte has 256 different patterns, enough for the numbers 0 to 255.Mix-up alert: A byte is 8 bits, not the other way round. A bit is the smaller one.See this in Key words. For example, 01000001 is one byte.
Computers use two states because a switch can reliably be on or off. Two states are easy for the hardware to tell apart.
BinaryA way of writing numbers with only TWO digits: 0 and 1.Exactly: A number system where each place value is a power of two: 1, 2, 4, 8 and so on. Computers store all data in binary.Mix-up alert: 1010 in binary is ten. It is not one thousand ten.See this in Key words is a number system that uses only two digits, 0 and 1. We use those digits to write down switch states.
Step-through
Do this: Step through the picture. Say each switch's state before you read the next step.
Eight light switches stand for eight tiny switches inside a computer. Watch how we write them down.
Whole picture, 5 steps
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Step-through
Do this: Step through the picture. At each stop, say what the switch was made of.
Computer logic uses switches that are on or off. Over the years the switches got smaller and faster, so computers could hold many more. The drawings are not to scale.
Whole picture, 5 steps
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Step-through
Do this: Step through the zoom. At each lens, say whether it is bigger or smaller than 54 nm.
How small are the parts of a chip? Zoom in one step at a time, from a hair down to atoms. Each lens is a bigger zoom, so the drawings are not to scale.
Whole picture, 6 steps
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Do this: Read this, then say in your own words what Gordon Moore predicted.
In 1975, Gordon Moore, a co-founder of Intel, predicted that the number of parts on a chip, like transistors, would roughly double about every two years. For decades, engineers roughly kept up. It is a trend, not a law of nature. Today it is harder, so engineers also join and stack chips.
Do this: Follow each step. Then read the switches yourself.
Theo looks at four switches. They read off, on, on, off.
He writes the pattern 0110. That is 4 bits, which is half of a byte, because a byte is 8 bits.
Do this: List the patterns for 2 switches. Then predict the count for 3.
Mia has 2 switches. She lists every pattern: 00, 01, 10 and 11. That is 4 patterns. Each extra switch doubles the count. 3 switches give 8 patterns, and 4 switches give 16. Keep doubling: 8 switches, one byte, give 256 different patterns.
Do this: Say which one is bigger, a bit or a byte.
A bit is not 8 bytes: it is the other way round. A ByteA group of 8 bits.Exactly: Eight bits handled together. One byte has 256 different patterns, enough for the numbers 0 to 255.Mix-up alert: A byte is 8 bits, not the other way round. A bit is the smaller one.See this in Key words is 8 bits. A BitOne 0 or 1. The SMALLEST piece of computer data.Exactly: A binary digit: a single 0 or 1. It records the state of one switch, off or on.Mix-up alert: A bit is not a byte. It takes 8 bits to make 1 byte.See this in Key words is just one 0 or 1, so a byte is bigger. Memory trick: a bit is just a little bit.
Do this: Explain what a 0 tells you about a switch.
A 0 does not mean empty, wrong or broken. It is a normal value: that switch is off. A pattern like 0000 is still 4 bits of data.
From other sites
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Code.org, about 6 minutes
Watch from 0:56 to 3:33
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TED-Ed, about 5 minutes
Watch from 0:31 to 1:04
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Try it
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Try a question about bits, bytes and patterns. Show the working if you get stuck.
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Write it
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Start here if it helps: Computers use two states because...
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Flashcards
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Think of a light switch.
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What are the two states of a switch?
On and off.
How do we write on and off?
On is 1 and off is 0.
What is a bit?
One 0 or 1. It is the smallest piece of computer data.
What is a byte?
A group of 8 bits.
How many bits are in 2 bytes?
16 bits, because 2 × 8 = 16.
Switches read off, on, off, on. What pattern is that?
0101. Off is 0 and on is 1.
How many different patterns can 4 bits make?
16. Each extra bit doubles the count: 2, 4, 8, 16.
Why do computers use only two states?
A switch can reliably be on or off, so two states are easy for the hardware to tell apart.
What does binary mean?
Writing data with only two digits, 0 and 1.
How many bits are in 4 bytes?
32 bits, because 4 × 8 = 32.
How many bytes are 24 bits?
3 bytes, because 24 ÷ 8 = 3.
Switches read on, on, on, on. What pattern is that?
1111. On is 1, so write one 1 for each of the four switches.
How many patterns can 2 bits make?
4: 00, 01, 10 and 11.
What does one extra bit do to the number of patterns?
It doubles it. Every existing pattern can end with the new bit off (0) or on (1), giving two choices for each pattern.
Is 0000 still data?
Yes. It is 4 bits with every switch off.
True or false
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Self-test
Do this: Answer every question. Read the explanation after each one.
8 questions. One at a time.
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Match
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Connect the ideas
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Classwork
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https://gradebridge-beryl.vercel.app/learn/csc/digital-representation-and-files/bits-and-switches#classwork
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https://gradebridge-beryl.vercel.app/learn/csc/digital-representation-and-files/bits-and-switches#homework
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