Why computers count in twos

Computing · Computing Fundamentals · ages 12-13

Name ______________________ Date ____________

What is a bit and what is a byte?
- A bit is one switch; a byte is eight bits
- A bit is eight switches; a byte is one switch
- A bit is a letter; a byte is a word
Why does a computer use only two symbols?
- Two symbols look prettier on screen
- Two states stay easy to tell apart in a circuit
- Two symbols need more switches
Ten voltage levels per switch would be more reliable than two.
Circle one: True False
Ben says five switches make 10 patterns because 5 plus 5 is 10. What is the correct rule?
- Switches cannot reach five at all
- Patterns add instead of doubling
- Patterns double per switch instead of adding
Two switches make 4 patterns. What do three switches make?
- 5
- 6
- 8
A toy has 4 switches, each on or off. You know 3 switches make 8 patterns. Type how many patterns 4 switches make.
Answer: ______________
Five switches build on four switches, and four switches make 16 patterns. Type the pattern count for five switches.
Answer: ______________
A byte holds 256 patterns. How many patterns do 9 switches hold?
- 257
- 512
- 264

Answer key

For grown-ups. Fold this page away before handing over the rest.

A bit is one switch; a byte is eight bits · Bit means one switch, byte means eight of them.
Two states stay easy to tell apart in a circuit · Two clearly split states survive noisy circuits.
False · Close levels blur, so ten states are less reliable.
Patterns double per switch instead of adding · Each switch doubles the count, so adding undercounts badly.
8 · Each extra switch doubles, so 4 doubles to 8.
16 · Double the 8 patterns once more to get 16.
32 · Doubling 16 once more gives 32.
512 · One more switch doubles 256 to 512.