← ACARA Digital Technologies Years 7–8

How storage keeps bits

Storage keeps each bit as one of two physical conditions, such as charged or not charged, magnetised one way or the other, or a pit or a flat area. One condition is 0 and the other is 1.

Part of: ACARA Digital Technologies Years 7–8 — Binary Number Representation — Module 28

Understanding How storage keeps bits in ACARA Digital Technologies Years 7–8

What it does: The surface has two physical conditions, so one is given the value 1 and the other the value 0. Each cell is in one of two conditions, so charged, not charged, not charged, charged is written as 1001. A memory chip uses tiny parts that are either charged or not charged. One state is 0 and the other is 1. A magnetic disk stores bits using the direction of magnetism. One direction is 0 and the other is 1. An optical disc has tiny pits and flat areas on its surface. A laser reads which one is there, so it can tell 0 from 1.

Common mistakes: A memory cell has only two conditions, so it can only hold a 0 or a 1. The line should be bit = 1, because 2 is not a binary digit. A single = stores a value in a variable. == only compares two values. The line should be bit = 0 to store the bit for this magnetic direction.

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This module's key terms are also in a printable crossword (Modules 204–236) and word search (Modules 189–236).

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Learning
Duo
How does a storage device keep a single bit?
As one of two physical conditionsAs one of ten physical conditions
Matches
north = 1, south = 1
↓
Both magnetic directions were given the same value, so the two conditions cannot be told apart. One must be 0 and the other 1.
Applying
Meanings
Term
two physical states
Meaning
Storage keeps each bit as one of two physical conditions, such as charged or not charged, magnetised one way or the other, or a pit or a flat area. One condition is 0 and the other is 1.
Practice
memory chip: charged = 1, not charged = 0
Testing
Gaps
A memory chip holds a bit as a or none
Check Answer
Spots
2if cell == 'charged':
3 bit = 2

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Quick Questions

1. How does a storage device keep a single bit?
A. As one of ten physical conditions
B. As one of two physical conditions ✓
Each bit is stored using just two physical conditions. One condition means 0 and the other means 1.
2. In a memory chip, which pair of conditions can hold a bit?
A. Hot or cold or warm
B. Charged or not charged ✓
A memory chip uses tiny parts that are either charged or not charged. One state is 0 and the other is 1.
3. On a magnetic disk, how is a bit kept?
A. By which way a tiny spot is magnetised ✓
B. By how bright a tiny spot is painted
A magnetic disk stores bits using the direction of magnetism. One direction is 0 and the other is 1.
4. On an optical disc such as a CD, which two conditions hold a bit?
A. A pit or a flat area ✓
B. A red spot or a blue spot
An optical disc has tiny pits and flat areas on its surface. A laser reads which one is there, so it can tell 0 from 1.
5. A tiny spot on a disk is magnetised one way. What does that tell us?
A. It holds one of the two bit values, 0 or 1 ✓
B. It holds a whole number from 0 to 9
One magnetic direction stands for 0 and the opposite direction stands for 1. A single spot only ever holds one bit.

Match the Pairs

charged → 1, not charged → 0 → A memory chip cell stores a bit by holding an electric charge or not holding one
north → 1, south → 0 → A magnetic disk stores a bit by which way a tiny spot is magnetised
A pit or a flat area on the surface of a disc can each stand for one bit → pit = 1, flat = 0
Four storage cells that are charged, not charged, not charged, charged hold a nibble → 1001
north = 1, south = 1 → Both magnetic directions were given the same value, so the two conditions cannot be told apart. One must be 0 and the other 1.
not charged = 0, half charged = 1, fully charged = 2 → Storage cells only have two conditions, so there is no half charged state and no value 2. A bit can only be 0 or 1.

Key Term

two physical states
Storage keeps each bit as one of two physical conditions, such as charged or not charged, magnetised one way or the other, or a pit or a flat area. One condition is 0 and the other is 1.

Fill in the Blanks

1. A memory chip holds a bit as a charge or none
Hint: Type the electrical thing a memory chip cell either holds or does not hold.
2. A disk stores a bit as magnetic direction
Hint: Type the word for which way the tiny magnetic area points.
3. Each bit has 2 physical conditions
Hint: Type the number of conditions a storage device uses for one bit.
4. Pit or flat area: one is 0, the other is 1
Hint: Type the other binary digit that is not 0.
5. IF cell is charged THEN bit = 1 ELSE bit = 0
Hint: Type the keyword that handles the other condition, when the cell is not charged.

Spot the Error

Question 1
A cell = 'charged'
B if cell == 'charged':
C bit = 2
D else:
E bit = 0
Line C — A memory cell has only two conditions, so it can only hold a 0 or a 1. The line should be bit = 1, because 2 is not a binary digit.
Question 2
A direction = 'north'
B if direction == 'north':
C bit == 0
D else:
E bit = 1
Line C — A single = stores a value in a variable. == only compares two values. The line should be bit = 0 to store the bit for this magnetic direction.
Question 3
A states = ['pit', 'flat']
B surface = 'flat'
C count = len(surface)
D print(count)
Line C — A disc surface has two possible conditions, pit or flat. The count should be taken from the states list with len(states), which gives 2. len(surface) counts letters.
Question 4
A states = ['charged', 'empty', 'half']
B print(len(states))
C # 2 states hold 0 or 1
Line A — A storage cell keeps a bit using only two physical conditions. The list should hold just 'charged' and 'empty'. A third state would not match the two digits 0 and 1.
Question 5
A bits = [0, 1, 2]
B for b in bits:
C print('stored', b)
Line A — A bit can only be 0 or 1, matching the two physical conditions. The list should be [0, 1]. A 2 does not exist in binary.

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