Computer Fundamentals Review

✅ What is Binary?

Binary is a base-2 number system that uses only:

• 0 (off)
• 1 (on)

Each digit in binary is called a bit.
In decimal, we use powers of 10. In binary, we use powers of 2.

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🔢 Decimal to Binary Logic (4-bit version for 0-9)

We’ll use 4-bit binary (i.e., 4 digits) because the largest decimal (9) fits inside 4 bits.

Bit Position	2³ (8)	2² (4)	2¹ (2)	2⁰ (1)
Binary Digit	?	?	?	?

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📋 Binary Table of 0–9

Decimal	Binary (4-bit)	Breakdown (2³ 2² 2¹ 2⁰)
0	0000	0+0+0+0
1	0001	0+0+0+1
2	0010	0+0+2+0
3	0011	0+0+2+1
4	0100	0+4+0+0
5	0101	0+4+0+1
6	0110	0+4+2+0
7	0111	0+4+2+1
8	1000	8+0+0+0
9	1001	8+0+0+1

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🧠 Easy Way to Remember

Think of each binary number as a combination lock where:

• First digit = 8s
• Second digit = 4s
• Third digit = 2s
• Last digit = 1s

Example:

• 1001 = 8 + 0 + 0 + 1 = 9
• 0110 = 0 + 4 + 2 + 0 = 6

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🎯 Memory Trick

You can memorize this like counting with your fingers in binary:

Finger Count	Binary	Mnemonic
0	0000	All off
1	0001	Only 1 is on
2	0010	Only 2 is on
3	0011	2 + 1
4	0100	Only 4 is on
5	0101	4 + 1
6	0110	4 + 2
7	0111	4 + 2 + 1
8	1000	Only 8 is on
9	1001	8 + 1