How storage keeps bits

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Quick Questions

Shade in the A or B circle for each question.

1. How does a storage device keep a single bit?

A As one of ten physical conditions

B As one of two physical conditions

2. In a memory chip, which pair of conditions can hold a bit?

A Hot or cold or warm

B Charged or not charged

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

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

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

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1charged → 1, not charged → 0		AStorage cells only have two conditions, so there is no half charged state and no value 2. A bit can only be 0 or 1.
2north → 1, south → 0		BBoth magnetic directions were given the same value, so the two conditions cannot be told apart. One must be 0 and the other 1.
3A pit or a flat area on the surface of a disc can each stand for one bit		CA memory chip cell stores a bit by holding an electric charge or not holding one
4Four storage cells that are charged, not charged, not charged, charged hold a nibble		DA magnetic disk stores a bit by which way a tiny spot is magnetised
5north = 1, south = 1		Epit = 1, flat = 0
6not charged = 0, half charged = 1, fully charged = 2		F1001

Definitions

two physical states

Fill in the Blanks

Complete each line of code by filling in the missing parts.

A memory chip holds a bit as a ______ or none

A disk stores a bit as magnetic _________

Each bit has _ physical conditions

Pit or flat area: one is 0, the other is _

IF cell is charged THEN bit = 1 ____ bit = 0

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A cell = 'charged'

B if cell == 'charged':

C bit = 2

D else:

E bit = 0

Question 2

A direction = 'north'

B if direction == 'north':

C bit == 0

D else:

E bit = 1

Question 3

A states = ['pit', 'flat']

B surface = 'flat'

C count = len(surface)

D print(count)

Question 4

A states = ['charged', 'empty', 'half']

B print(len(states))

C # 2 states hold 0 or 1

Question 5

A bits = [0, 1, 2]

B for b in bits:

C print('stored', b)

Answer Key

How storage keeps bits

Section A: Quick Questions

B — As one of two physical conditions

B — Charged or not charged

A — By which way a tiny spot is magnetised

A — A pit or a flat area

A — It holds one of the two bit values, 0 or 1

Section B: 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.

Section C: Definitions

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.

Section D: Fill in the Blanks

A memory chip holds a bit as a charge or none

A disk stores a bit as magnetic direction

Each bit has 2 physical conditions

Pit or flat area: one is 0, the other is 1

IF cell is charged THEN bit = 1
ELSE bit = 0

Section E: Spot the Error

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.

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.

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.

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.

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.